ESP8266 : An IoT System on Chip

Triple Server Update – Part 1: Serving Arduino


Happy New Year! I’m picking things up right where they ended last year…

There were some basic enhancements needed to my Triple Protocol Server. But in the process of implementing the updates, the limitations of the ESP8266 resources were reached. To make room for the new features, something had to go.

In this case, the CoAP server was eliminated. The choice was obvious. This protocol consumed a large chunk of the available heap, leaving little room for program execution. As result, the system became unstable. CoAP also does not lend itself easily to web browser based clients.

So with that gone, a valuable new feature was added. A light-weight modification that did not significantly burden the system. Something that Arduino users should find extremely useful.

What is it?

An Arduino Serial Port Web Server

What? We already have access from the Arduino using the AT command set. “So what’s so special about this?”, you say.

Well…this implementation removes most of the web server tasks from the Arduino and puts it in the ESP8266. The only thing the Arduino needs to do is read small strings (requests) from the ESP8266 and return a small string back. This frees the Arduino to concentrate on sensor readings and control functions.

This balances the load on the two micro-controllers, reducing the load on the Arduino while fully leveraging the available power of the ESP8266 as a web server.

So how does this work?

It’s really quite simple. The ESP8266 web server is already in place. All that is needed is a few new URL-based (or MQTT topic payload) commands to provide web-based access to the Arduino resources.

The New Arduino Commands

The commands are parsed and decoded by the ESP8266. The command is reduced to a small string that is passed to the Arduino for action with it’s hardware resources.

URL Suffix ESP8266 to Arduino Arduino Reply
Set Digital Channel 04 HI /?arduino=SetDigital&chan=04&state=1 Arduino_SD041 Digital Channel 04 is HI
Get Digital Channel 04 /?arduino=GetDigital&chan=04 Arduino_GD04 Digital Channel 04 is HI
Get Analog Channel 04 /?arduino=GetAnalog&chan=04 Arduino_GA04 Analog Channel 04 is 2.234

The Arduino returns a reply to the ESP8266, which, in turn, is returned to the http or mqtt client.

This structure is similar to the slash (/) delineated bridge interface used with the Arduino Yun to communicate between it’s Arduino and Linux processors. Instead of using a pricey Arduino Yun, you can use any model Arduino along with the very inexpensive ESP8266. In this test case, I used a $7 Arduino nano clone.

The example presented here only includes the basic digital and analog access to the Arduino. The digital interface is obvious, setting or reading the state of each pin. The analog channel reads returns a voltage between 0 and 5 volts, based on the 10-bit Arduino ADC channel reading.

From this command set, it should be obvious how to expand it to include bus oriented sensors such as 1-wire temperature and i2c connected devices.

ESP8266 Sketch

The ESP8266 Arduino IDE sketch is based upon my triple server sketch presented in a prior post. The default parameters are defined at the top of the sketch in the section titled “Initial EEPROM Values”. These can be revised to match your network setting as described in Part 2 of this post, and in the sketch’s github repository.

Additional code was needed to support the Arduino requests. The commands received are repacked into a small string to be sent to the Arduino via the ESP8266 serial port. The server code to process the three recognized requests (Set Digital, GetDigital and Get Analog) shown here can easily be expanded for addition requests:

  1. // -----------------------------------------------------------------------
  2. // Serving Arduino via serial port
  3. // -----------------------------------------------------------------------
  4. if(os_strcmp(pURL_Param->pParam[0], "arduino")==0) {
  5. //-------------- Request = SetDigital ---------------------
  6. if(os_strcmp(pURL_Param->pParVal[0], "SetDigital")==0){
  7. if(os_strcmp(pURL_Param->pParam[1], "chan")==0) {
  8.           ArduinoRequest = "Arduino_SD";
  9.            ArduinoRequest += pURL_Param->pParVal[1];
  10.         }
  11.        else {
  12.             ArduinoRequest = "Invalid Request";  
  13.         }
  14.         if((os_strcmp(pURL_Param->pParam[2], "state")==0)&&(os_strcmp(
  15. ArduinoRequest.c_str(), "Invalid Request")!=0)) {
  16.             ArduinoRequest += pURL_Param->pParVal[2];
  17.         }
  18.         else {
  19.             ArduinoRequest = "Invalid Request";  
  20.         }
  21. }
  22.     //-------------- Request = GetDigital ----------------------
  23.     else if(os_strcmp(pURL_Param->pParVal[0], "GetDigital")==0){
  24. if(os_strcmp(pURL_Param->pParam[1], "chan")==0) {
  25.          ArduinoRequest = "Arduino_GD";
  26.             ArduinoRequest += pURL_Param->pParVal[1];
  27.      }
  28.       else {
  29.             ArduinoRequest = "Invalid Request";  
  30.      }
  31.    }
  32.     //-------------- Request = GetAnalog ----------------------
  33.     else if(os_strcmp(pURL_Param->pParVal[0], "GetAnalog")==0){
  34.      if(os_strcmp(pURL_Param->pParam[1], "chan")==0) {
  35.          ArduinoRequest = "Arduino_GA";
  36.             ArduinoRequest += pURL_Param->pParVal[1];
  37.         }
  38.         else {
  39.             ArduinoRequest = "Invalid Request";  
  40.         }
  41.    }
  42.    //-------------- Request is not recognized -----------------
  43.    else {
  44.     ArduinoRequest = "Invalid Request";  
  45.    }
  46.    //-------- Execute valid request & get reply string --------
  47.    if(os_strcmp(ArduinoRequest.c_str(), "Invalid Request")==0) {
  48.      payld = ArduinoRequest;
  49.    }
  50.    else {
  51.     rparam.request = ARDUINO_REQUEST;
  52.        rparam.requestval = 0;
  53.        Server_ExecuteRequest(servertype, rparam, &payld, ArduinoRequest);
  54.   }
  55.   Server_SendReply(servertype, REPLY_TEXT, payld);
  56. }

Arduino Sketch

A simple Arduino sketch is provided here  as an example of how to receive and process requests from the ESP8266. Using the low-end Arduino nano, this example uses a software serial port (Arduino digital pins 10 and 11) to communicate with the ESP8266.

Due to the limited bandwidth for reliable operation with this software port, the baud was reduced to 1200 baud. If a dedicated hardware serial port is used, such as found with the Arduino mega, the baud can be increased considerably.

The example provided is fully functional, yet simple enough to understand and build upon with even modest programming skills.

Part 2: Web-based ESP8266 Configuration

So there you have it, an ESP8266 web server sketch that supports Arduino communication using either MQTT or url-based http protocols. But there is more to this update. I’ve also added web-browser configuration of the Network and MQTT settings.

Read on here for the details…

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ESP8266 Triple Protocol Server


In my previous post, a comparison was made between ESP8266 Http and MQTT hosted servers. But the evaluation was not complete…it did not include CoAP. So I decided to add CoAP to the ESP8266 server sketch and revisit the performance.

Like MQTT and Http, CoAP is deployed in IoT things for M2M communication. But what is it?

Simply stated, CoAP, or Constrained Application Protocol is a web communication structure designed for use with limited resource Internet Things. For some light reading (zzzz) with all the details, refer to RFC 7252 upon which it is based. This protocol is designed to be light-weight, using connection-less UDP over IP.

But this is not a CoAP tutorial.

The purpose of this article is to compare the performance of CoAP with my previous comparison of MQTT to Http. To keep things on a level playing field, CoAP was evaluated using the same server get command that we used to test MQTT and Http servers.

Building on the initial design, the dual server sketch was simply updated to include CoAP. This example now supports three IoT communication protocols: CoAP, Mqtt and http. And just as before, there are two build options for the http server; one using the Arduino Wifi library for ESP8266 and the other using the EspressIf SDK API.

And as is the case with many of my first-time endeavors, an unexpected finding was uncovered…

Triple Protocol Server Sketch

Since this was my first attempt with a CoAP implementation, I started out searching for a suitable example as a basis for the sketch. Fortunately, there was one available, microcoap. That library is used in my sketch. It turned out to be a bit more than a trivial library addition to the sketch.

In addition to the sketch changes, the CoAP protocol required 3 new files;

  1. coap.h       - Header file for coap library
  2. coap.c       - Coap library code
  3. endpoints.c  - CoAP interface for this example sketch

The coap.h,c files were added to the Arduino library while the endpoints.c is added to the sketch folder.

All of the typedefs and #defines were moved from the sketch to a separate header file; sketch.h.

The CoAP communication relies on UDP over IP. While a callback is preferred, this CoAP implementation requires polling in the loop() function to check for incoming CoAP packets. This added step to the 3-protocol server loop() function is implemented in the function “ProcessCOAPMsg()”.

  1. void loop() {
  2.     util_startWIFI();                    // Connect wifi if connection dropped
  3.     #if MQTT_SVR_ENABLE==1
  4.     MqttServer_Processor();              // Service MQTT
  5.     #endif
  6.     #if SVR_TYPE==SVR_HTTP_LIB
  7.     ArduinoWebServer_Processor();        // Service Web Server
  8.     #endif
  10.     ProcessCOAPMsg();                    // Service CoAP Messages
  11.     ReadSensors(2500);                   // Read 1 sensor every 2.5 seconds or longer
  12. }

But there is one way to reduce the loop() tasks. Fortunately, we have the option of  using the SDK for the web server, which uses callbacks instead of polling in loop(). As you can see, the pre-compiler directive only includes the web server in loop() when the LIB option is selected. The callback is executed anytime an external http connection is made, eliminating the need to poll in loop().

In order to add some functionality to the original server, a fourth command was added to the 3 included with the dual mqtt and http server:

  1. Turn LED On
  2. Turn LED Off
  3. Get Sensor Values
  4. Blink LED n times

The added command in this example serves two new purposes:

First, this was an opportunity to have a command example that also required a parameter, In this case, the “blink” command needs a parameter to identify the number of blinks to perform.

Secondly, this command needs to be run asynchronous with the server reply. So that the reply is complete while the LED blinks continued. This would also be the case for any command that may require significant time to complete. Requiring a server reply before the command execution finishes.

In this case, a non-blocking function is launched using a timer. The timer receives a parameter identifying how many times remain in the blink sequence, as well as the state (on or off) to set the LED. Each time the timer is called (with a 500 ms delay to provide time for the observer to see the LED state), the LED changes state and the timer is called again. This continues until the commanded number of blinks finishes.

  1. ********************************************************
  2.  * Callback for Blink timer
  3.  * Function: BlinkCallback(int *pArg)
  4.  * 
  5.  * Parameter    Description
  6.  * ---------    -----------------------------------------
  7.  * *pArg        int - number of times to blink LED
  8.  * *pArg+1      int - set LED state (0=off,1=on) 
  9.  * *pArg+2      int - set to 1 first time to print header 
  10.  * return       no return value
  11.  ********************************************************/
  12. void BlinkCallback(int *pArg) {
  13.     int i;
  14.     int nblinks,ledstate,start;
  16.     nblinks = *(int *)pArg;                           // Number of LED blinks
  17.     ledstate = *(int *)(pArg+1);                      // LED state to program
  18.     start = *(int *)(pArg+2);                         // Set to 1 first time this is 
  19. called
  20.     if(start == 1)
  21.     {
  22.         Serial.print("Blink countdown:");             // LED countdown header to serial port
  23.         blinkarg[2] = 0;                              // Do not print header next time
  24.     }
  25.     if(ledstate==1)
  26.     {
  27.          Serial.print( nblinks);                      // Current Blink number
  28.          if(nblinks>1) 
  29.          {
  30.              Serial.print(".");                       // Blink countdown separator
  31.          }
  32.          else
  33.          {
  34.              Serial.println("...");                   // Separator after last blink
  35.          }
  36.          digitalWrite(LED_IND, HIGH);                 // Set LED On
  37.          blinkarg[1] = 0;                             // Set LED off next time
  38.          os_timer_arm(&BlinkLedTimer, 500, false);    // Execute this function 1 time 
  39. after 500 ms
  40.     }
  41.     else
  42.     {
  43.          digitalWrite(LED_IND, LOW);
  44.          blinkarg[1] = 1;                             // start with led on cmd
  45.          if(--nblinks!=0) {                           // Execute until blinks remaining  is 0
  46.             --blinkarg[0];                            // Decrement remaining blinks 
  47.             os_timer_arm(&BlinkLedTimer, 500, false); // Execute this function 1 time 
  48. after 500 ms
  49.          }     
  50.     }
  51. }

Ready to download this Arduino IDE server code?

You can get the triple CoAP, MQTT & HTTP Web Server sketch and associated files here.

CoAP Server

The commands the CoAP server responds to is defined in the file “endpoints.c” All the methods for the CoAP server are defined in the “endpoints array:

  1. //////////////////////////////////////////////////////////////////////////
  2. // Define all CoAP Methods for this Server
  3. //////////////////////////////////////////////////////////////////////////
  4. const coap_endpoint_t endpoints[] =
  5. {
  6.     {COAP_METHOD_GET, handle_get_well_known_core, &path_well_known_core, "ct=40"},
  7.     {COAP_METHOD_GET, handle_get_light, &path_light, "ct=0"},
  8.     {COAP_METHOD_GET, handle_get_light_blink, &path_light_blink, "ct=0"},
  9.     {COAP_METHOD_GET, handle_get_request, &path_request, "ct=0"},
  10.     {COAP_METHOD_PUT, handle_put_request, &path_request, NULL},
  11.     {COAP_METHOD_PUT, handle_put_light, &path_light, NULL},
  12.     {COAP_METHOD_PUT, handle_put_light_blink, &path_light_blink, NULL},
  13.     {(coap_method_t)0, NULL, NULL, NULL}
  14. };
  15. The function names, starting with "handle_", identify the callbacks executed when a request is received corresponding

The function names, beginning with “handle_”, identify the callbacks executed when a request is received corresponding the service path. And the service paths which are returned from CoAP “Discovery” requests are defined in this file for each method:

  1. //////////////////////////////////////////////////////////////////////////
  2. // Define URI path for all CoAP Methods for this Server
  3. //////////////////////////////////////////////////////////////////////////
  4. static const coap_endpoint_path_t path_well_known_core = {2, {".well-known", "core"}};
  5. static const coap_endpoint_path_t path_light_blink = {1, {"light_blink"}};
  6. static const coap_endpoint_path_t path_request = {1, {"request"}};
  7. static const coap_endpoint_path_t path_light = {1, {"light"}};

The list can be expanded to meet your own custom server requirements. In order to test the CoAP server in operation, a CoAP client is needed.

CoAP Client

My initial plan was to expand the html/Javascript test page used to compare Mqtt with http servers to include CoAP.  But every implementation found required an http to CoAP proxy. This proved to be more challenging to implement than I had planned. At this time, I was unsuccessful. This may come later. But for now, for this evaluation, I settled for a browser plugin. The choices were limited. That is to say, only one was available.

It is called Copper (Cu) CoAP user-agent. At this time, it is only supported with the Mozilla Firefox browser.

Installation is simple:

First, if not already on your computer,  you need to install the Mozilla Firefox browser.

Then, using this browser open the URL “” and click on the “+ Add to Firefox” button.

So how do we use this client?

Fortunately, the interface to the ESP8266 CoAP server is easy to access with this plugin. Once added to Mozilla Firefox, start the ESP8266 with the triple server sketch running and enter the following into the browser URL field:


Of course, if you have your own domain pointing to your broadband connection with your router configured to forward port 5683 to your ESP8266, you would enter:

coap://<your domain>:5683/

This will open your interactive CoAP interface tool. It should appear initially similar to this:


A nice feature of the CoAP protocol is discovery. Click on the Discover button for the CoAP server (our ESP8266 device) to report back the services it will support:


The command/response mechanism is straightforward. Click on one of the 3 services shown, enter the “Outgoing” payload, and click on the PUT button. The ESP8266 CoAP server reply will appear at the “Incoming” payload tab. Here are all the services & payloads supported.

Service Payload Server Reply
Turn LED on light 1 1
Turn LED off light 0 0
Blink LED 3 times light_blink 3 3
Turn LED on request /?request=LedOn LED is now ON
Turn LED off request /?request=LedOff LED is now OFF
Blink LED 6 times request /?request=BlinkLed&nblink=6 LED is now blinking 6 times.
Get Sensor values request /?request=GetSensors JSON Sensor values string

The “request” service supports identical commands for all three server types. Again, to keep things consistent, the “GetSensors” request will be used for this evaluation, the same command that was used for the dual server test.

In that case, select the “request” service, enter /?request=GetSensors in the Outgoing payload window, and click on the “PUT” button.


The response (Incoming payload) will be the same as the reply received using the MQTT or HTTP servers:


Response Delay Evaluation

For the MQTT and HTTP servers, a simple web page, using only html and JavaScript was used to measure the delay from the time a request was sent to the time the reply was received. The web page file is called “mqtt_server.html”; it is on GitHub here.

And the CoAP server evaluation used the Firefox Modzilla browser plug-in.

MQTT and HTPP Response Time

With mqtt_server.html open, the time starts when the button is clicked to send a request to the server. When the reply is received, the end time-stamp was captured. But what I found was that this end stamp was not saved immediately, resulting in inaccurate readings. This is likely due to the asynchronous nature of JavaScript. To correct this, a 1 second callback was added from the time the reply time-stamp was captured to the time the lapse time was calculated. This resulted in repeatable results which appear to accurately report the response delay.

CoAP Response Time

The response time is reported directly from the Firefox Mozilla tool when a request was sent by clicking on the “Put button. The time is referenced as RTT in the Mozilla windows in the format:

<IP or domain name>:5683 (RTT: 26 ms)

In this example, the response time was 26 ms.


Ten requests were made for each of the three server setups. The average of the ten readings are shown in this table:

Sample 1 23 361 273 54
Sample 2 23 322 488 96
Sample 3 125 315 505 39
Sample 4 271 360 537 58
Sample 5 27 409 482 63
Sample 6 99 423 559 94
Sample 7 12 345 488 59
Sample 8 11 333 455 102
Sample 9 10 325 434 36
Sample 10 103 325 329 21
Average 70 352 455 62

The time is measured in milliseconds. From this experiment, the HTTP SDK API and CoAP servers offer significantly less latency than either the HTTP Wifi Library or MQTT. From this, we can conclude that callbacks that do not use the sketch loop() function are more efficient. And the UDP over IP result in faster replies than TCP connections when polling is used, but reply at comparable speeds when HTTP callbacks are used.

The Unexpected Discovery

As I mentioned in the beginning, an unexpected discovery was made in the course of this evaluation. Unfortunately, it is not a good thing, but it must be told. Hopefully, this may allow someone to avoid the pitfall. This finding was made using Arduino IDE version 1.6.5. Later versions might have corrected the issue.

This has to do with the HTTP Wifi Library based server. What I have found is that with every server request made, the system heap shrinks. This is returned as the “SYS_Heap” value (bytes) from a “GetSensors” request. The bytes do not return to the heap for a while, sometimes minutes later, sometimes, it appears never to be relinquished.

What does this mean?

Well, if requests are made often enough, the heap will shrink to the point that the ESP8266 resets, sometimes without recovery (crashes). None of the other server types presented here exhibit any heap shrinkage from receiving and replying to request.

I checked this with some of my earlier Arduino IDE sketches. Regretfully, they all exhibit this same heap shrinkage when server requests are made.

Recommendation: Avoid using the HTTP Wifi Library based server. Instead, use the EspressIf SDK API, similar to what has been presented in this sketch.

Especially if you have experienced unexplained ESP8266 crashes or resets when your sketch runs for an extended period of time. The depletion of the heap could definitely be the root cause.

In Closing

As you can see from the results, CoAP performs well as compared to polling MQTT and HTTP servers.

CoAP is indeed a viable option as an IoT M2M communication protocol, This method provides a solution that is lightweight, fast and there are many implementation options available. Unfortunate, these options do not directly include client side JavaScript webpages. A proxy is needed to translate the UDP CoAP to http. This proxy would undoubtedly slow down the message transfers, but this alone is unlikely to be significant enough to discount CoAP.

And as “lightweight” as CoAP is intrinsically, the implementation code is more complex and lengthy than any other server.

I hope this example provides anyone interested with a framework to pursue ESP8266 CoAP communications further. My next step will to create custom CoAP clients. For my needs, two platforms will be useful. An Android based smartphone App and a browser solution accessible from any browser.

How would you use best use CoAP with your ESP8266 IoT thing?

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ESP8266 HTTP vs MQTT Servers


The ability to communicate with your IoT things — to send commands and receive responses is an essential pillar of your “connected” system. You need a network link to control things and to read sensors. Two of the most common Internet to machine communication protocols used with the ESP8266 and other MCUs are http and MQTT.

There are advantages and drawbacks using either one of these methods.

So which one is better?

For an assessment, I created a simple Arduino IDE sketch with just two metrics in mind for the evaluation. First was the simplicity of the application code. How clean was the framework needed to implement the server?

The other concern was latency. That is, how long  is required from the time of a client request to server reply? I was curious to measure this time. Is the delay magnitude in the order of milliseconds, or seconds?

The Sketch

I started out with the intent on creating two sketches; one of an http server and one for MQTT. But what became apparent was that other than the code needed to connect, read and write to the protocol, the software was almost identical. So for simplicity and efficiency, the http and MQTT servers were combined into a single sketch.

This also made the evaluation easier-there was no need to reload the firmware to switch protocols.

The typical Arduino IDE based http server requires the use of two class objects. These objects are defined in WiFi.h for Arduino based systems and the ESP8266WiFi.h library for the ESP8266.

  • WiFiServer
  • WiFiClient

The major shortcoming with the Arduino IDE library is the need in the user sketch to poll for new connections in the loop(). It would be far more efficient to register a callback function that is executed upon an external client connection. Like the EspressIf SDK Iot_demo example web server.

This constraint alone would be sufficient justification to use the Espressif SDK over the Arduino IDE for all but the simplest Web Server application.

Fortunately, however, there is a way to use the SDK callbacks with the Arduino IDE. Here is how it is done. That is just what we will use for comparing the http and MQTT servers. The sketch for this test is just a reuse of that sketch with the added code needed to support MQTT. The Dual MQTT & HTTP Web Server code is here.

Code Assessment

When looking at the code structure for the MQTT broker vs the Arduino Wifi library vs the SDK API, the most efficient design was the SDK API. While all 3 methods worked well, the SDK design uses a callback to service client connections without any code needed in the loop() function.

The Arduino Wifi library requires polling for connections each iteration of loop().

And sure, the MQTT broker server, like the SDK API, also uses callbacks. But it still requires the execution of “client.loop()” in the sketch’s loop() function. This consumes bandwidth which undoubtedly will add latency to other tasks added to loop().

If loop() latency becomes an issue in your sketch, use of the SDK API web server callbacks will minimize the delays.

Response Delay Evaluation

A simple web page, using only html and JavaScript was used to measure the delay from the time a request was sent to the time the reply was received. The web page file is called “mqtt_server.html”; it is on GitHub here.

The time starts when the button is clicked to send a request to the server. When the reply is received, the end time-stamp was captured. But what I found was that this end stamp was not saved immediately, resulting in inaccurate readings. This is likely due to the asynchronous nature of JavaScript. To correct this, a 1 second callback was added from the time the reply time-stamp was captured to the time the lapse time was calculated. This resulted in repeatable results which appear to accurately report the response delay.

Twelve requests were made for each of the three server setups. The average of the twelve, and the average of ten with the high and low readings removed are shown in this table:

Sample 1 429 89 341
Sample 2 457 32 362
Sample 3 367 30 338
Sample 4 441 85 383
Sample 5 365 42 375
Sample 6 400 28 417
Sample 7 465 26 343
Sample 8 489 445 333
Sample 9 620 42 566
Sample 10 358 32 339
Sample 11 731 212 325
Sample 12 432 29 432
Average of 12 463 91 380
Average of 10(w/o Hi & Lo) 447 62 366

The time is measured in milliseconds. From this experiment, it is clear that the SDK API offers significantly less latency than either the Wifi Library or MQTT. From this, it should be clear that callbacks that do not use the sketch loop() function are more efficient.

In Closing

There are advantages and shortcomings when using either MQTT or http for web server applications. MQTT offers a clean and simple code interface, but it does require the use of a broker. That adds an additional layer of complexity and potential failure to your system.

In my opinion, MQTT is best suited to be used for data distribution, not as a web server. The MQTT publish/subscribe model works great to simultaneously send information from one source to many consumers. If speed is critical, the EspressIf SDK API is the best option to use the ESP8266 as a web server.


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ESP8266 Arduino IDE Web Server Using Callbacks


While the Arduino IDE is a convenient and familiar platform to develop ESP8266 Web Server based projects, it does have a significant drawback. That is, once the Web Server is started, it is necessary to poll the server each iteration of the loop() function to check for new connections before processing the request.

Putting the check in a loop with other activities, such as reading sensors could and often does result in significant response delays. And possible loss of communication due to connection timeouts.

A better approach is to use a callback that fires whenever an external client connects to the ESP8266 server. This frees up the sketch loop() from the task of servicing http request using inefficient polling code.

And callbacks is how a Web Server is implemented using the ESP8266 EspressIf SDK. But why is it missing from the Arduino IDE? I suspect it is because that is the way it is done with Arduino-based systems—making it both familiar and perhaps suitable for Arduino code reuse with the ESP8266.

But it is not the best solution for new designs.

So that got me thinking…

Why not customize the typical web server sketch to use the SDK callback schema? After all, it is possible to  call ESP8266 SDK functions from the Arduino IDE. While searching, I could not find any examples of this being done, so I’ve created one myself.

And here it is…

The SDK Server Architecture

The SDK API requires several layers of callbacks in a web server design. Since these callbacks are usable in a sketch without modification, the actual sketch functions included in this example are shown.

First,  the server must be setup in the sketch setup() routine. This initialization code was encapsulated in the following function, “SdkWebServer_Init()”, called in setup():

  1. void SdkWebServer_Init(int port) {
  2.     LOCAL struct espconn esp_conn;
  3.     LOCAL esp_tcp esptcp;
  4.     //Fill the connection structure, including "listen" port
  5.     esp_conn.type = ESPCONN_TCP;
  6.     esp_conn.state = ESPCONN_NONE;
  7.     esp_conn.proto.tcp = &amp;esptcp;
  8.     esp_conn.proto.tcp-&gt;local_port = port;
  9.     esp_conn.recv_callback = NULL;
  10.     esp_conn.sent_callback = NULL;
  11.     esp_conn.reverse = NULL;
  12.     //Register the connection timeout(0=no timeout)
  13.     espconn_regist_time(&amp;esp_conn,0,0);
  14.     //Register connection callback
  15.     espconn_regist_connectcb(&amp;esp_conn, SdkWebServer_listen);
  16.     //Start Listening for connections
  17.     espconn_accept(&amp;esp_conn); 
  18. }

Upon an external TCP connection, the callback “SdkWebServer_listen” is executed:

  1. void SdkWebServer_listen(void *arg)
  2. {
  3.     struct espconn *pesp_conn = ( espconn *)arg;
  4.     espconn_regist_recvcb(pesp_conn, SdkWebServer_recv);
  5.     espconn_regist_reconcb(pesp_conn, SdkWebServer_recon);
  6.     espconn_regist_disconcb(pesp_conn, SdkWebServer_discon);
  7. }

This functions registers 3 connection-specific callbacks:

  1. SdkWebServer_recv – Called when connection data is received. This callback replaces the polling loop when using the Arduino library.
  2. SdkWebServer_recon – Called when TCP connection is broken.
  3. SdkWebServer_discon-Called when a TCP connection is closed.

The SdkWebServer_recv() function processes http GET and POST requests in a similar manner as the processing in the loop() after an Arduino client connection is detected.

Putting It All Together

In order to contrast the commonly used Arduino Web Server library with the SDK API, I’ve put together an example sketch that supports both web server approaches. It’s on Github:

ESP8266-12 Arduino IDE Web Server Example 

This example provide the same functionality with either server interface. The selection is made prior to building the sketch, using precompilation directives. When possible, the same code is used with both selections. The difference is that the SDK uses callbacks while the Arduino polls for connections.

While no additional hardware is needed to run and test the Web Server, this example assumes the ESP8266 circuit from this post. But the code will work with any ESP8266 circuit, even with no externally connected sensors or controls. But without the ADC multiplexer from the referenced post, the ADC will simply make the same measurement for each multiplexer setting. Which is just fine for the purposes of this example.

Testing the Server From A Web Browser

Since both versions of the Web Server provide the same functionality, the same test can be performed for verification.

You might need to changed the static IP set in this example to match your own LAN subnet. The defaults are currently set to:


Listen Port: 9701

The test url is thus:

And the JSON returned from the Web Server should be in the following format:


And if connected, the server will also support changing the LED on/off state:

To turn it on, use the URL:

And the off URL i:

Adding server functionality should be obvious after reviewing the sketch.


Using a callback to process Web Server connection requests is far superior to polling. CPU bandwidth is only used in response to client connection events. And with the example framework provided in this post, you can still utilize many of the Arduino sensor libraries without modification.

With a Web Server application, you get the efficiency of the callback with the familiarity of the Arduino IDE.

I hope you find this information useful…

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ESP8266 MQTT Publication & External Subscription


Publishing data produced by ESP8266 sensors to an MQTT broker server is a great option to making your IoT data visible to outside consumers with minimal consumption of precious MCU bandwidth. Simple, easy to implement and very light-weight.

What a great distribution system!

Simply publish your ESP8266 sensor data once, and many subscribers can consume the information, virtually at the same time. Sweet!

MQTT Basics

In case you are new to MQTT, here are a few basics. MQTT is the acronym for message queuing telemetry transport. Now that’s a mouthful! It is essentially a protocol that follows the publish/subscribe model to distribute information from one source to many users.

Here’s a few links for more MQTT information:

I’ve put together an ESP8266 MQTT demo project using an Arduino IDE sketch to publish data for consumption by subscribers using the MQTT protocol. Several options for consuming the data as a subscriber are also presented…

MQTT Broker/Server

For demo purposes, I wanted to use a free broker. After testing a few of the available options, I settled on using the Mosquitto MQTT server. While unsecured, meaning anyone who knows your “topic” can subscribe to the data, it works great for a proving out your design.


port: 1883

Arduino IDE Sketch

There is one library that needs to be added to the Arduino IDE to access the MQTT broker. It’s called “PubSubClient”. Here is how to install it…

Step 1: Open the Arduino IDE

Step 2: From the menu, select Sketch>Include Library>Manage Libraries…

Step 3: Enter “PubSubClient” in the search box.


Step 4: Click on the “Install” button

Now that was easy.


But there is one more thing to do  after installing PubSubClient. I have found that the default maximum packet size (128 bytes) is insufficient. You should at least double it to 256 bytes.


Just open the file “…/Arduino/libraries/pubSubClient/src/PubSubClient.h and change the following line:





Now lets talk about the sketch to test MQTT with the ESP8266…

The setup() function performs 3 basic tasks:


  • setup serial port
  • connect to wifi
  • set MQTT broker/server

And loop() maintains the Wifi and MQTT connections, reads the sensors, and publishes the values to the MQTT broker.


  • Reconnect to WiFi if disconnected
  • Reconnect to MQTT broker/server if disconnected
  • Read Sensor(s)
  • Publish Sensor data

Here is a break-down of the sketch. First, the objects must be identified

  1. #include &lt;ESP8266WiFi.h&gt;
  2. #include &lt;PubSubClient.h&gt;
  3. #define wifi_ssid "Your SSID"
  4. #define wifi_password Your Wifi password"
  5. #define mqtt_server ""
  6. #define mqtt_user "not used in this example"
  7. #define mqtt_password "not used in this example"
  8. #define topic1 "t1"
  9. #define topic2 "t2"
  10. WiFiClient espClient;
  11. PubSubClient client(espClient);

And then the sketch setup…

  1. void setup() {
  2.    Serial.begin(115200);
  3.    setup_wifi();
  4.    client.setServer(mqtt_server, 1883);
  5. }

A typical Wifi connect function:

  1. void setup_wifi() {
  2.    delay(10);
  3.    // We start by connecting to a WiFi network
  4.    Serial.println();
  5.    Serial.print("Connecting to ");
  6.    Serial.println(wifi_ssid);
  7.    WiFi.begin(wifi_ssid, wifi_password);
  8.    while (WiFi.status() != WL_CONNECTED) {
  9.      delay(500);
  10.      Serial.print(".");
  11.    }
  12.    Serial.println("");
  13.    Serial.println("WiFi connected");
  14.    Serial.println("IP address: ");
  15.    Serial.println(WiFi.localIP());
  16. }

The loop() simply makes sure a connection to the MQTT is made, reads the sensors, and publishes the results. The publish rate is set at 2 seconds minimum.

  1. void loop() {
  2.   if (!client.connected()) {
  3.     reconnect();
  4.   }
  5.   client.loop();
  6.   //2 seconds minimum between Read Sensors and Publish
  7.   long now = millis();
  8.   if (now - lastMsg &gt; 2000) {
  9.       lastMsg = now;
  10.       //Read Sensors (simulated by increasing the values, range:0-90)
  11.       t1 = t1&gt;90 ? 0 : ++t1;
  12.       t2 = t2&gt;90 ? 0 : ++t2;
  13.       //Publish Values to MQTT broker
  14.       pubMQTT(topic1,t1);
  15.       pubMQTT(topic2,t2);
  16.   }
  17. }

Just copy and paste this complete sketch as a starting template to test your own MQTT publishing with the ESP8266. Remember, you will need to set the WIFI ssid & password in the sketch to your access point values before running.

  1. #include &lt;ESP8266WiFi.h&gt;
  2. #include &lt;PubSubClient.h&gt;
  3. #define wifi_ssid "YOURSSID"
  4. #define wifi_password "YOURPASSWORD"
  5. #define mqtt_server ""
  6. #define mqtt_user "your_username"
  7. #define mqtt_password "your_password"
  8. #define topic1 "t1"
  9. #define topic2 "t2"
  10. WiFiClient espClient;
  11. PubSubClient client(espClient);
  12. void setup() {
  13.    Serial.begin(115200);
  14.    setup_wifi();
  15.    client.setServer(mqtt_server, 1883);
  16. }
  17. void setup_wifi() {
  18.    delay(10);
  19.    // We start by connecting to a WiFi network
  20.    Serial.println();
  21.    Serial.print("Connecting to ");
  22.    Serial.println(wifi_ssid);
  23.    WiFi.begin(wifi_ssid, wifi_password);
  24.    while (WiFi.status() != WL_CONNECTED) {
  25.      delay(500);
  26.      Serial.print(".");
  27.    }
  28.    Serial.println("");
  29.    Serial.println("WiFi connected");
  30.    Serial.println("IP address: ");
  31.    Serial.println(WiFi.localIP());
  32. }
  33. void reconnect() {
  34.    // Loop until we're reconnected
  35.    while (!client.connected()) {
  36.      Serial.print("Attempting MQTT connection...");
  37.      // Attempt to connect
  38.      if (client.connect("TestMQTT")) { //* See //NOTE below
  39.        Serial.println("connected");
  40.      } else {
  41.        Serial.print("failed, rc=");
  42.        Serial.print(client.state());
  43.        Serial.println(" try again in 5 seconds");
  44.        // Wait 5 seconds before retrying
  45.        delay(5000);
  46.      }
  47.    }
  48. }
  49. //NOTE: if a user/password is used for MQTT connection use:
  50. //if(client.connect("TestMQTT", mqtt_user, mqtt_password)) {
  51. void pubMQTT(String topic,float topic_val){
  52.     Serial.print("Newest topic " + topic + " value:");
  53.     Serial.println(String(topic_val).c_str());
  54.     client.publish(topic.c_str(), String(topic_val).c_str(), true);
  55. }
  56. //Variables used in loop()
  57. long lastMsg = 0;
  58. float t1 = 75.5;
  59. float t2 = 50.5;
  60. void loop() {
  61.   if (!client.connected()) {
  62.     reconnect();
  63.   }
  64.   client.loop();
  65.   //2 seconds minimum between Read Sensors and Publish
  66.   long now = millis();
  67.   if (now - lastMsg &gt; 2000) {
  68.       lastMsg = now;
  69.       //Read Sensors (simulate by increasing the values, range:0-90)
  70.       t1 = t1&gt;90 ? 0 : ++t1;
  71.       t2 = t2&gt;90 ? 0 : ++t2;
  72.       //Publish Values to MQTT broker
  73.       pubMQTT(topic1,t1);
  74.       pubMQTT(topic2,t2);
  75.   }
  76. }

Testing Tools

While there are many tools available, here are a few I have found that you can use to verify the ESP8266 is actually publishing the data.


Simply subscribe to the topic and watch the information updates in real-time.

Google Chrome Application

First try using MQTTLens, an off-the-shelf tool to subscribe to the published data. You can get MQTTLens here. Although this app is installed via Google Chrome, it runs as standalone application. At this time, Chrome apps are supported using Windows, Mac and Linux operating systems.

This app provides basic functionality for testing MQTT publish/subscribe messages.

Once the app has been installed and started, a few configuration steps are needed to connect to our MQTT broker and subscribe to the ESP8266 published topics.

Just click on the configuration icon and fill in the information as shown below:
Once you are connected to the broker, the only thing left to do is subscribe to the data feed. For this example, two topics are published by the ESP8266; t1 and t2. Enter one of these and click on the subscribe button to monitor the data as it is published.
Notice you can change the number of messages displayed using the “-+” icons.

Web Page using JavaScript

MQTTLens is a great tool to get a quick look at your MQTT published data. But when you move from merely testing the data feed to developing a custom application, full control to manipulate and display the information is essential.
Fortunately, this is a simple task using only JavaScript and html.
I’ve developed the following html code to subscribe to the ESP8266 published data. This may be useful as a template on your own website. Simply open a file with this code in a web browser to test. Name this file as you please, using “.html” as the file name extension. In this example, I have named the file “mqtt_subscribe.html”.

  1. &lt;!DOCTYPE html&gt;         
  2. &lt;html&gt;         
  3. &lt;head&gt;         
  4. &lt;title&gt;MQTT JavaScript Client Example&lt;/title&gt;         
  5. &lt;!-- Latest compiled and minified CSS - add here as needed --&gt;         
  6. &lt;/head&gt;         
  7. &lt;body&gt;         
  8. &lt;!-- HTML to display MQTT topic values --&gt;         
  9. &lt;div&gt;&lt;strong&gt;Published ESP8266 topics via MQTT:&lt;/strong&gt;&lt;/div&gt;&lt;br&gt;         
  10. &lt;div id="t1"&gt;&lt;/div&gt;         
  11. &lt;div id="t2"&gt;&lt;/div&gt;         
  12. &lt;!-- mosquitto MQTT --&gt;         
  13. &lt;script type="text/javascript" src=""&gt;&lt;/script&gt;         
  14. &lt;!-- jQuery --&gt;         
  15. &lt;script src=""&gt;&lt;/script&gt;         
  16. &lt;!-- Custom MQTT client for this example --&gt;         
  17. &lt;script&gt;         
  18. // Create a client instance         
  19. client = new Mosquitto();         
  20. // Connect to MQTT broker         
  21. var url = "ws://";         
  22. client.connect(url);         
  23. // Callback executed upon connection         
  24. client.onconnect = function(rc){         
  25. var topic = 't1';         
  26. client.subscribe('t1', 0);         
  27. client.subscribe('t2', 0);         
  28. };         
  29. //Callback executed upon disconnection         
  30. client.ondisconnect = function(rc){         
  31. client.connect(url);         
  32. };         
  33. //Callback executed upon receipt of MQTT message         
  34. client.onmessage = function(topic, payload, qos){         
  35. if(topic=="t1") {         
  36. $("#t1").html("Topic: t1 Value: " + payload);         
  37. }         
  38. if(topic=="t2") {         
  39. $("#t2").html("Topic: t2 Value: " + payload);         
  40. }         
  41. };         
  42. &lt;/script&gt;         
  43. &lt;/body&gt;         
  44. &lt;/html&gt;

Just to keep things clean and simple, no css styling is included in this example. Here is a snapshot of the browser windows when this file is viewed:



While I have not yet explored the development of a custom Android App to interface with an MQTT broker, it is certainly possible. What immediately comes to mind, in the spirit of App portable, would be to develop an Android Cordova App. This would allow you to reuse the above html code, without modification.
Here is my step-by-step guide to get started.
But if you are looking for an off-the-shelf MQTT test application, I recommend using MyMQTT . This is a free App available in Google Play Store. Once installed, there are only a few steps needed to subscribe to the ESP8266 example MQTT feed.
The App will startup with the following screen:
First set the app to connect with the broker we are using for this example. Click on “Settings” and enter the broker information as shown:
Then subscribe to the ESP8266 published topics (t1 and t2):
The dashboard will then display the topic data as it is published:


MQTTInspector is the most popular App to test MQTT feeds from an iOS device. At $1.99, is not free, yet certainly low-cost. As a Windows, Android and Linux user, I cannot provide any additional information regarding this tool. It appears to be similar to other MQTT client test tools, and can be found on iTunes here.

In Conclusion

Here you have it. A simple guide to publishing topics from an ESP8266 device to an MQTT broker. All you need is a simple Arduino IDE sketch.

Once published, this data feed can be consumed cross-platform, on any device that supports MQTT. From this article, this includes but is certainly not limited to Windows, Mac and iOS. There are also Linux packages available to support MQTT clients.

As always, I hope you find this information useful…

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ESP8266 Dual AT & Web Server Mode

Here is an exciting framework for fully utilizing the huge capabilities of the ESP8266.

This is an original.

Something that I have not seen anywhere before. You see, using this structure opens up many more possibilities and applications for this amazing device…

Most folks in the ESP8266 world seem to fall into one of two camps. The first group, typically diehard Arduino developers, want to use the ESP8266 as a serial to WIFI shield. A couple bucks to add WIFI to the very popular Arduino platform is most cost effective method of bringing it on-line. Much cheaper than alternative WiFi shields.

Others see the ESP8266 as a complete solution. It is often referred to as a System On a Chip (SoC). They not only use the ESP8266 for WIFI internet access, but also use the platform to read sensors, control “things”, process data and provide web server functionality.

Among The Examples

The majority of those that have delved into the ESP8266 world started by loading the serial to WIFI firmware often referred to as the AT command set. This is available as a binary file downloaded to the ESP8266 via it’s serial interface. That’s where I began my ESP8266 journey.

It was not long after my start that I searched for the AT firmware source code. Fortunately, it is available within earlier versions of the EspressIf SDK. You see, prior to version 1.0, many example applications were included in the development package. And yes, the AT command set was among these examples.

The other most useful example application is the IoT_Demo. This software has survived every release of the SDK, including the current version. This example provides a framework for a web server to make your “things” Internet accessible.

After studying the software structure of these examples I got to thinking…

Wouldn’t it be great to merge these two applications? So you benefit from both features?

It indeed did look feasible.

The combined application would not only service AT commands through the serial port, but also service http GET or POST commands via the Internet.

And that’s not all…

This single ESP8266 firmware application could also be used to read sensors and control devices.

I am stoked to say I have successfully merged these examples. This broadens the capabilities and applications of a single ESP8266 based system.

It works!

Here’s how…

ESP8266 Dual Server Architecture

The ESP8266 is used to perform 3 primary functions. First, it provides basic serial to Wifi capability using the standard AT command set that many first-time users tinker with. Note that since the design presented here includes the AT firmware source code, the command set can be expanded to also provide access to the Esp8266 Daq and Control features. This is depicted in the following diagram as two-way arrows from the AT Server.


The ESP8266 also provides Web Server functionality. This feature operates completely independently from the serial AT Server. The web server responds to http GET commands received form the Internet via the built-in Wifi capability. Just like the AT Server, the Web Server has access to the Daq and Control functions.

And finally, the data acquisition (DAQ) and control function, also running independently from the other two features, controls all the Esp8266 outputs and receives all the sensor inputs. Because of the many possible sensors connected to the system, the DAQ function must be managed so that it does not monopolize the Esp8266 processor. This is accomplished by limiting it’s execution to the reading of one sensor each time the function is called.

Task Distribution

Separate callbacks are registered for each of the three ESP8266 primary functions. Both the AT and Web Server callbacks are event driven. They are only executed upon user request. The AT callback is executed anytime data is received on the serial port, while the Web Server callback is run upon receipt of an http GET request.

The callback for the Daq/Control features are different. This feature is set up to execute periodically (once every second) from a Timer callback. This keeps the sensor data fresh, available for consumption by the AT or Web Server, upon request.

AT Callback – The AT serial port server callback is installed in the uset_init() function when at_init() is executed. The AT server responds to any of the requests defined in at_cmd.h.

  1. at_funcationType at_fun[at_cmdNum]={
  2. {NULL, 0, NULL, NULL, NULL, at_exeCmdNull},
  3. .
  4. .
  5. {"+CIPSERVER", 10, NULL, NULL,at_setupCmdCipserver, NULL},
  6.   {"+CIPMODE", 8, NULL, at_queryCmdCipmode, at_setupCmdCipmode, NULL},
  7.   {"+CIPSTO", 7, NULL, at_queryCmdCipsto, at_setupCmdCipsto, NULL},
  8.   {"+CIUPDATE", 9, NULL, NULL, NULL, at_exeCmdCiupdate},
  9.   {"+CIPING", 7, NULL, NULL, NULL, at_exeCmdCiping},
  10.   {"+CIPAPPUP", 9, NULL, NULL, NULL, at_exeCmdCipappup},
  11.   {"+GETSENSOR", 10, NULL, NULL, at_exeGetSensorVal, NULL},

The new request, “+GETSENSOR”, has been added to provide a method for the serial port server to get the sensor readings. Upon receiving this request, the function at_exeGetSensorVal() is called. This function returns the current sensor reading over the ESP8266 serial port.

  2. at_exeGetSensorVal(uint8_t id, char *pPara)
  3. {
  4.       int isensno = atoi(++pPara);
  5.       switch(isensno) {
  6.             case 1:
  7.                   uart0_sendStr(tInside);
  8.                   break;
  9.             case 2:
  10.                   uart0_sendStr(tOutside);
  11.                   break;
  12.             case 3:
  13.                   uart0_sendStr(tAttic);
  14.                   break;
  15.             case 4:
  16.                   uart0_sendStr(tDht11);
  17.                   break;
  18.             case 5:
  19.                   uart0_sendStr(hDht11);
  20.                   break;
  21.             case 6:
  22.                   uart0_sendStr(pBmp085);
  23.                   break;
  24.             case 7:
  25.                   uart0_sendStr(tBmp085);
  26.                   break;
  27.             case 8:
  28.                   uart0_sendStr(aBmp085);
  29.                   break;
  30.             default:
  31.                   uart0_sendStr("out of range");
  32.                   break;
  33.       }
  34.       uart0_sendStr("\r\n");
  35. }

The requests are made by sending the following string over the serial port:


“n” is the sensor number and corresponds to the case number in the code above.

As you can see, it is not difficult to add your own custom commands to the standard ESP8266 AT command set.

Web Server Callback – This application uses the Web Server code provided in the IoT_Demo example. The user_init() function sets up and connects to the local Wifi before launching the Web Server. The callback webserver_recv() is registered during the initialization sequence. That function is executed any time an http GET request is received.

For this demo application, the Web Server only responds to “request-GetSensors”. More requests can be added as noted in the code that follows. When received, the server replies by sending a JSON string containing all the sensor readings.

  2. webserver_recv(void *arg, char *pusrdata, unsigned short length)
  3. {
  4.     URL_Param *pURL_Param = NULL;
  5.     char *pParseBuffer = NULL;
  6.     bool parse_flag = false;
  7.     struct espconn *ptrespconn = arg;
  8.     int i;
  9.     espconn_set_opt(ptrespconn, ESPCONN_REUSEADDR);
  10.     if(upgrade_lock == 0){
  11.           parse_flag = save_data(pusrdata, length);
  12.         if (parse_flag == false) {
  13.               response_send(ptrespconn, false);
  14.         }
  15.         pURL_Param = (URL_Param *)os_zalloc(sizeof(URL_Param));
  16.         parse_url_params(precvbuffer, pURL_Param);
  17.         switch (pURL_Param-&gt;Type) {
  18.             case GET:
  19.                 if(os_strcmp(pURL_Param-&gt;pParam[0], "request")==0) {
  20.                     <strong>// GetSensors is the only request the server currently supports</strong>
  21. <strong>                    if(os_strcmp(pURL_Param-&gt;pParVal[0], "GetSensors")==0) {</strong>
  22. <strong>                          json_send(ptrespconn, GET_SENSORS);</strong>
  23. <strong>                    }</strong>
  24.                     // Add additional requests here
  25.                 }
  26.                 json_send(ptrespconn, CONNECT_STATUS);
  27.                 break;
  28.             case POST:
  29.                   ets_uart_printf("We have a POST request.\n");
  30.                  break;
  31.         }
  32.         if (precvbuffer != NULL){
  33.               os_free(precvbuffer);
  34.               precvbuffer = NULL;
  35.         }
  36.         os_free(pURL_Param);
  37.         pURL_Param = NULL;
  38.     }
  39.     else if(upgrade_lock == 1){
  40.           local_upgrade_download(ptrespconn,pusrdata, length);
  41.             if (precvbuffer != NULL){
  42.                   os_free(precvbuffer);
  43.                   precvbuffer = NULL;
  44.             }
  45.             os_free(pURL_Param);
  46.             pURL_Param = NULL;
  47.     }
  48. }


Acquisition/Control Timer Callback – This callback serves as the application’s periodic loop() function. It is called once every second. The functions is mechanized as a state machine. In this example, 5 states are implemented, one for each sensor in the system. Exactly one state is executed each time the function is called. Upon completion of the sensor read, the code is set to execute the next state the next time the function is called. The code can be modified as needed to add or delete states and sensor hardware.

  1. LOCAL void ICACHE_FLASH_ATTR loop_cb(void *arg)
  2. {
  3.     char szT[32];
  4.     DHT_Sensor DHsensor;
  5.     DHT_Sensor_Data data;
  6. = 5;  //GPIO14
  7.     DHsensor.type = DHT11;
  8.     int32_t temperature;
  9.     int32_t pressure;
  10.     //---------------------------------------------------
  11.     //This state machine reads 1 sensor each iteration
  12.     //---------------------------------------------------
  13.       switch(nTcnt%5) {
  14.             case 0: //Read first DS18B20 Temperature Sensor
  15.                 get_temp_ds18b20(1,1,tInside);
  16.                 break;
  17.             case 1: //Read second DS18B20 Temperature Sensor
  18.                 get_temp_ds18b20(2,1,tOutside);
  19.                 break;
  20.             case 2: //Read third DS18B20 Temperature Sensor
  21.                 get_temp_ds18b20(3,1,tAttic);
  22.                 break;
  23.             case 3: //Read DHT11 temperature and humidity Sensor
  24.                 DHTRead(&amp;DHsensor, &amp;data);
  25.                 DHTFloat2String(tDht11, ((9/5) * data.temperature)+32);
  26.                 DHTFloat2String(hDht11, data.humidity);
  27.                 break;
  28.             case 4: //Read BMP085 Temperature and pressure Sensor
  29.                 temperature = BMP180_GetTemperature();
  30.                 pressure = BMP180_GetPressure(OSS_0);
  31.                 os_sprintf(pBmp085,"%ld.%01d", pressure/3386,(pressure%3386)/1000);
  32.                 os_sprintf(tBmp085,"%ld.%01d", ((temperature*18)/100) + 32,(temperature*18)%100);
  33.                 os_sprintf(aBmp085,"%03d", 328 * (BMP180_CalcAltitude(pressure)/100000));
  34.                 break;
  35.             default:
  36.                 break;
  37.       }
  38. }

Want the code for this framework? Please feel free to use and modify it for your own custom requirements. It is available on Github here.

Testing the Code

Let’s test the dual server by sending a command over the serial port and via http GET. The command will retrieve sensors values read by the ESP8266. For this test case, the 1 second loop() function has been modified as follows to populate the sensor variables without actually reading any sensors.

  1. LOCAL void ICACHE_FLASH_ATTR loop_cb(void *arg)
  2. {
  3.     //-----------------------------------------------------
  4.     //This test code populates the variables associated
  5. //with the sensor values in lieu of actually reading
  6. //sensors. This code is used to test the functionality
  7. //of the dual server application. All variables are
  8. //set with fixed values except iTinside, which is
  9. // incremented by 1.5 degrees each time this function
  10. //is called.
  11.     //-----------------------------------------------------
  12. if(tI&lt;800) {
  13. tI += 15;
  14. }
  15. else {
  16. tI = 600;
  17. }
  18. os_sprintf(tInside,"%d.%d",tI/10,tI%10); //Sensor 1
  19. os_sprintf(tOutside,"%s","79.2"); //Sensor 2
  20. os_sprintf(tAttic,"%s","88.5"); //Sensor 3
  21. os_sprintf(tDht11,"%s","69.1"); //Sensor 4
  22. os_sprintf(hDht11,"%s","34.7"); //Sensor 5
  23. os_sprintf(pBmp085,"%s","29.7"); //Sensor 6
  24. os_sprintf(tBmp085,"%s","71.1"); //Sensor 7
  25. os_sprintf(aBmp085,"%s","555.0"); //Sensor 8
  26. }

AT Serial Server Test

The added function in this demo application to the AT command set is “AT+GETSENSOR=n”. “n” is filled in with an integer value representing the sensor number. Enter the following to test this new command:

Sensor Serial Port Command Expected Reply
Inside Temperature AT+GETSENSOR=1 increasing value in range 60-80 F
Outside Temperature AT+GETSENSOR=2 79.2
Attic Temperature AT+GETSENSOR=3 88.5
DHT11 Temperature AT+GETSENSOR=4 69.1
DHT11 Humidity AT+GETSENSOR=5 34.7
BMP085 Pressure AT+GETSENSOR=6 29.7
BMP085 Temperature AT+GETSENSOR=7 71.1
BMP085 Altitude AT+GETSENSOR=8 550.0

Web Server Test

The web server can easily be tested by entering a single URL in any web browser. In this demo application, the IP is hard-coded to “” and the server responds to port 9703 requests. Thus, the test URL is:

And the expected reply will be the following JSON string:

  1. {
  2. "B_Pressure":"29.7",
  3. "B_Temperature":"71.1",
  4. "B_Altitude":"555.0",
  5. "DS_TempInside":"79.5", &lt;--NOTE: This value will range from 60-80 F in 1.5 degree increments
  6. "DS_TempOutside":"79.2",
  7. "DS_TempAttic":"88.5",
  8. "DH_Humidity":"34.7",
  9. "DH_Temperature":"69.1"
  10. }

Your demo application is working properly if the expected responses are observed.

In Closing

This opens up new possibilities. With this structure, you use the ESP8266 as an Arduino serial to WIFI shield. Yet at the same time use this same ESP8266 as a web server. And a sensor acquisition engine. And to control “things”. All you need to do is add meat to the bones provided here. What will you come up with?

I hope you find this information useful…

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ESP8266 Free Space Assessment


Have you ever used the EspressIf SDK to compile code and wondered how much free space you have? How much more code you can add before running out of memory?

That information is very useful when developing code, and is readily available when using the Arduino IDE. So why is it missing from the SDK console output when you execute a build?

That used to bug me, until I figured out how to include it. Read on if you want a better view of the free space available after building your ESP8266 code.

Here is how I did it…

Evaluating Solution Options

First thing I did was review the Makefile that was provided with the SDK examples. I thought it might be a simple matter of adding a few lines to output the desired information. After all, the current Makefile outputs the number of byte used. And we know how much memory is available. A simple calculation and boom, you got the answer.


What I found was that the current memory statistics are generated by the utility “MemAnalyzer.exe” . This tool is included with the EspressIf SDK. So I figured all that it would take was a few changes to this utility to format the memory statistics in the format I wanted. Problem is, the source code for this utility is nowhere to be found. At least I had no luck finding it.

So what I decided to do was create another utility. One that would format the information provided by MemAnalyzer.exe and include it in the build Console output.

The Solution

Obviously, this requires some changes to the project’s “Make” file. The current information, while I find it inadequate, is produced by the following Makefile file line:

  1.  $(Q) $(SDK_TOOLS)/memanalyzer.exe $(OBJDUMP).exe $@

And the output from the memanalyzer tool is displayed like this example:

  1.    Section|              Description| Start (hex)| End (hex)|Used space
  2. ------------------------------------------------------------------------------
  3.       data|   Initialized Data (RAM)|    3FFE8000|  3FFE8D8C|    3468
  4.     rodata|      ReadOnly Data (RAM)|    3FFE8D90|  3FFEA3F4|    5732
  5.        bss| Uninitialized Data (RAM)|    3FFEA3F8|  3FFF4C08|   43024
  6.       text|       Cached Code (IRAM)|    40100000|  4010782C|   30764
  7. irom0_text|      Uncached Code (SPI)|    40240000|  4026F574|  193908
  8. Total Used RAM : 52224
  9. Free RAM : 29696
  10. Free IRam : 2022

In order to access this information, it was redirected to a text file (mem.txt) by adding a new line to the MakeFile:

  1. $(Q) $(SDK_TOOLS)/memanalyzer.exe $(OBJDUMP).exe $@
  2. <strong><span style="color: red;">$(Q) $(SDK_TOOLS)/memanalyzer.exe $(OBJDUMP).exe $@ &gt;mem.txt</span></strong>

My new utility reads the mem.txt file and outputs the re-formatted memory statistics to the build Console. The utility is named “EspMemUsage.exe” and is called in the Makefile with the addition of a second line:

  1. $(Q) $(SDK_TOOLS)/memanalyzer.exe $(OBJDUMP).exe $@
  2. $(Q) $(SDK_TOOLS)/memanalyzer.exe $(OBJDUMP).exe $@ &gt;mem.txt
  3. <strong><font style="color: red;">$(Q) $(SDK_TOOLS)/EspMemUsage.exe $(OBJDUMP).exe $@</font></strong>

And here is what the added Console output information looks like:

  1. ------------------------------------------------------------------------------
  2. Resource            |Size(bytes)|    Used|       %Used|        Free|   %Free
  3. --------------------|-----------|--------|------------|------------|----------
  4. IRAM - Cached Code  |      32768|   30746|          94|        2022|       6
  5. SPI - Uncached Code |     253952|  193908|          76|       60044|      24
  6. RAM - Data          |      81920|   52224|          63|       29696|      37
  7. ------------------------------------------------------------------------------

It help me a lot to see the memory usage in this format. I hope you find it useful too.

The utility, makefile, and source code are available on Github here. Installation instructions are provided in the readme file. It was developed using the free Microsoft code development  tool Visual Studio 2015 Community. Customize as you see fit to meet your specific needs and wants.

What It Does

The utility code is written using the c# programming language. The Program class is structured into 3 static functions.

  1. Main – This console application executes Main upon entry.  Main opens the file “mem.txt” and reads each line separately. If the line contains a memory value of interest, the information is extracted and formatted for output by calling the function “MemStat”. After completing the evaluation of the file “mem.txt”, the formatted results are output to the console.
  2. MemStat – This function extracts the value from the line read. Any spaces in the extracted value are removed by calling the 3rd and final function, “RemoveSpaces”. The memory used and free statistics are then calculated and formatted. The formatted string is returned to the function caller.
  3. RemoveSpaces – Removes spaces from a string.

In Closing

The utility presented here provides clarity to the ESP8266 code developer using the EspressIf SDK. So you know exactly how much memory is available for expansion, delineated by memory resource. Once installed, all you need to do is use the modified Makefile in your new projects to get the information displayed in the console output.

I hope you find this information useful.


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Capturing ESP8266 Max Value on ThingSpeak

This article provides a method to capture and store the maximum value reached in a ThingSpeak channel field.

So what’s the big deal? You’ve got all the data captured. Just retrieve the data points and search for the maximum among them. Well, read on…

You see, like many users, my ThingSpeak channel receives data captured by an ESP8266 micro-control unit (MCU). Both ESP8266 System Status and Sensor data are collected.

One of my key data points of interest is the lapse time between ESP8266 resets. The value is saved to the ThingSpeak channel in a field containing the ESP8266 ms running time. This, along with the sensor data is added to the channel data once each hour.

What I found was that reading all of the captured data and searching through it for a maximum value became increasingly slower as my database record count grew. It needed to run quicker. So I came up with a simple solution…

A method of comparing each new ESP8266 reading with the maximum value saved in a ThingSpeak channel field. This requires a CRON script running on my web server. The script is executed once every 20 minutes. What? It’s really not that complicated.

Here’s the details…

System Overview

The system is comprised of an ESP8266, a web host server capable of running CRON scripts, and a ThingSpeak channel. The CRON script is the key component used to move the information from the ESP8266 to the ThingSpeak channel.

The ESP8266 runs it’s own firmware serving two primary purposes. Periodically, it refreshes sensor readings and various system parameters, including the MCU run time since the last reset. This process runs on an internally registered timer callback.

The ESP8266 also acts as a web server. In this capacity, the server responds to http GET requests, returning sensor and system values in JSON format.

It should be noted here that this is not limited to an ESP8266. Any MCU capable of these two functions can be used.



So what exactly is a CRON script?

CRON originated in the Unix world. In this case, it is simply a service provide by the web host to automatically execute a script at a predetermined time. There are a couple of  options available to deploy automated scripts for data exchange to a ThingSpeak channel.

Organically, ThingSpeak provides the TimerControl App to perform an action at a specific time or on a regular schedule. This, along with the ThingSpeak ThingHTTP App is all that is needed. ThingHTTP interacts with the micro-controller using http GET or POST.

But there is a limitation with this approach…

You see, in my case, I also need to interface with a mySQL database. And ThingSpeak does not provide an API for that purpose. At least not yet. Sure, a proxy interface could be developed using a php script, that would unnecessarily  complicate the design. So I have used a different approach.

For this discussion, the CRON script uses php to interface both with ThingSpeak and a mySQL database. This eliminates the need for a proxy to overcome the ThingSpeak App’s lack of a mySQL interface. But even this approach comes with restrictions…

In order to prevent excessive resource consumption, my web host limits my account to three scheduled scripts.

The other stipulation is that the scripts cannot run continuously. The job should execute and complete within a “reasonable” amount of time. For this simple case, less than 10 seconds should be required.

The script tasks are simple and straight-forward…

  1. Read the current ESP8266 Sensor and status values (HTTP GET)
  2. Write the Sensor and status values to ThingSpeak
  3. Write all values to the mySQL database
  4. Read the max run-time value from ThingSpeak
  5. Evaluate whether current value for run-time is greater than the max value saved
  6. Write the max value back to ThingSpeak
  7. Write the other sensor and status values to ThingSpeak
  8. Write all values to the mySQL database

And here is the script.

PHP mySQL/ThingSpeak interface
  1. &lt;?php
  2.     include("sensors_weather_save_utils.php");
  3.     $diostatus = "";
  4.     define("MAXONTIME", 420); //7 minutes (60 * 7)
  5.     //----------------------------------------
  6.     //-----Get current Epoc time (to local)
  7.     //----------------------------------------
  8.     $now = time();
  9.     date_default_timezone_set('America/Los_Angeles');
  10.     $localtime_assoc = localtime(time(), true);
  11.     $current_hr = $localtime_assoc['tm_hour'];
  12.     $current_mn = $localtime_assoc['tm_min'];
  13.     //----------------------------------------
  14.     //specific time tasks
  15.     //----------------------------------------
  16.     if( $current_mn==0 ) {
  17. //Save Home Weather Sensors to database on-the-hour
  18.         require 'sensors_weather_save.php'; 
  19.     }
  20.     if( ($current_hr==7) &amp;&amp; ($current_mn==20) ) {
  21. //Now lets turn off the front porch light if it is 7:20 am
  22.         require 'iot_dtdoff.php'; 
  23.     }
  24.     //----------------------------------------
  25.     //Run every 20 minutes)
  26.     //----------------------------------------
  27.     //Check max time: Get ms since ESP8266 started
  28.     $temp_tm = getEsp8266Sensor($Esp8266SensorURL,"Y","SYS_Time");
  29.     //Get Thingspeak Channel 45834 field1:Max System Time)
  30.     $ThingsSpeakURL = ""."45834".
  31. "/feed/last.json?api_key=".$thingspeak45834;
  32.     $max_up = getEsp8266Sensor($ThingsSpeakURL,"Y","field1");
  33.     if($temp_tm &gt; $max_up) {
  34.      //Update ThingSpeak field1
  35.         $ThingsSpeakURL = "".$thingspeak45834.
  36. "&amp;field1=".$temp_tm;
  37.         get_fcontent($ThingsSpeakURL);
  38.     }
  39.     $status = file_get_contents($modtronixURL);
  40.     $status_array = json_decode($status);
  41.     //----------------------------------------
  42.     //-----find the dio port f byte value-----
  43.     //----------------------------------------
  44.     foreach($status_array as $key =&gt; $value) {
  45.         if(strstr($key,"pf")) {
  46.          $diostatus .= $value;
  47.         }
  48.     }
  49.     $diostatus = "B".$diostatus; //Binary prefix
  50.     //----------------------------------------
  51.     //-----get the dio port f byte last value
  52.     //----------------------------------------
  53.     // Connect to database (host,username,password,databasename) 
  54. // "@" suppresses errors/warnings
  55.     $link = @mysqli_connect("localhost",$mysqlUser,$mysqlPass,$mysqlUser);
  56.     //check if connection errors
  57.     if(mysqli_connect_error() ) {
  58.      die("Error: Could not connect to database"); //stops php script
  59.     }
  60.     //Selects(takes something out of database) everything(*) from the users table
  61.     $query = "SELECT * FROM myhome";
  62. if($result = mysqli_query($link, $query)) { //returns "TRUE" if successful
  63. $row = mysqli_fetch_array($result);
  64.     }
  65.     //----------------------------------------
  66.     //-----Get database status
  67.     //----------------------------------------
  68.     $laststatus = $row[PortF]; //Get Last Port F Status
  69.     $lasttime = $row[timetag]; //Get Last Epoc time
  70.     //----------------------------------------
  71.     //-----clear dio if no change
  72.     //----------------------------------------
  73.     $lapsesec = $now - $lasttime;
  74.     echo ($lapsesec);
  75.     if($diostatus != "B11111111") {
  76.     if($lapsesec &gt; MAXONTIME) {
  77.             file_get_contents($resetportfURL); //Reset Port F (Sprinklers off)
  78.         }
  79.     }
  80. //----------------------------------------
  81.     //-----update database status
  82.     //----------------------------------------
  83.     $query = "UPDATE `myhome` SET `PortF` = '".$diostatus."' WHERE id=0 LIMIT 1";
  84.     mysqli_query($link, $query);
  85.     $query = "UPDATE `myhome` SET `timetag` = '".$now."' WHERE id=0 LIMIT 1";
  86.     mysqli_query($link, $query);
  87. ?&gt;

This script runs every 20 minutes. And while the topic of this post is saving a max value, the other tasks performed by my script are also shown. I figured this would arm you with some actually used ideas on what is possible using a scheduled script to interact with your “things”.

As you can see, for example, the values are read and saved every hour using the “sensors_weather_save.php” script, while at 7:20 am, my dusk to dawn porch light is turned off. I found this necessary, especially on darker or overcast days. Physically, a bright LED is flashed briefly in front of the light sensor to extinguish the light, if it is on-simply by controlling a digital output signal.

The script to save values to mySQL is not shown. In lieu of that, the mySQL interaction exposed in the script illustrates the php interface. Here, it is used to turn off my sprinklers, if they remain on for more than 7 minutes. The check is made every 20 minutes. This was necessary as a watchdog in the event the sprinklers, under IoT control, were inadvertently left or stuck on.


This information provides a method to automatically update the max value of a ThingSpeak channel field. It also illustrates how to interface with a mySQL database using php. This php bridge script can be used to analyse and manipulate ThingSpeak data in any way needed.

Taking this the next logical step, I am planning a follow-up post to use the ThingSpeak Timer and ThingHTTP to accomplish the same thing within the ThingSpeak framework. This will, however, require the added complexity of a php proxy in the absence of a ThingSpeak mySQL API.

Stay tuned for that…

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IR Remote Using ESP8266

Even though I live alone, there are 4 TVs spread around my house. And since only 1 set is needed at a time, only one DVR box is needed. So I used a 1-4 HDMI splitter/driver to distribute the signal from the one box to the 4 TVs. Using the attic pathway, direct connections were made to each of the sets. It was pleasing to see that the active HDMI splitter could drive the remote TVs without any pixelation or frame freezes. The furthest HDMI cable required 100 feet. But here was the problem…

The remote would only work when pointed directly at the DVR. Sure, my Att-Uverse service includes a free smartphone App to use as a remote control for the other TVs. But that experience is not the same as using the physical remote that you get with the DVR.

I did have one IR transmitter/receiver pair that I purchased off-the-shelf. Works great! But at nearly $50, it just seemed a bit cost prohibitive to add additional pairs for the other 2 sets. So that got me thinking…

Hmmm. A micro-controller would work. But the relatively high cost of an Arduino, Raspberry Pi or Particle WIFI enabled system was unappealing. So this looked like another opportunity to deploy the low cost ESP8266 as a solution. Here is what I came up with…

IR Remote Solution using ESP8266

Initially, I wanted a system that used an ESP8266 positioned locally at the TV set, one setup for each television. The system would use an IR sensor to read the remote code to determine which button was pressed. Then, the ESP8266 code would take advantage of the AT&T U-verse® Enabled SDK. This interface would, based on the button pressed, send commands to the DVR, over an internet connection.


But there was a problem…

You see, the SDK only supports mobile apps using iOS or Android platforms. While I believe there is a way to port the java-based SDK to the ESP8266 embedded platform, it is not an endeavor I wish to pursue at this time. That’s the problem-it will take too much time. I was hoping that ATT would provide the solution.

So I sent a request to ATT to provide an SDK suitable for micro-controller use. We shall see what they have to say about that. You never know unless you ask…

Plan B: Adding another ESP8266 at the DVR

In order to move forward with this project, an alternate approach was needed. One that could be totally controlled within the framework of a micro-controller system. Without the need for a 3rd-party API.

I really just came up with a tweak of the original concept. Instead of using the ATT SDK, the IR commands would be sent to the second ESP8266 setup, using an web-server client command. This added unit, functioning as a web server, would be responsible for receiving the remote control commands and then transmitting the corresponding IR code to the DVR, using an IR Diode similar to the type found in remote controllers.


ESP8266 IR Remote Hardware Configuration

Here is the schematic of the circuit I used to check out the ESP8266 IR Send/Receive software.


The left side of the ESP8266 is the standard design I use for all projects. It has proven to be very stable, with hundreds of flash cycles completed successfully and no unintended resets during operation.

Three LEDs are used in the circuit:

  1. Status LED – A standard LED used to provide visual feedback.
  2. IR Tx LED – Sends IR data to the DVR
  3. IR Rx LED – Receives IR data from the DVR remote control.

In addition, a simple push-button switch is used to send the last code saved to the DVR.

This circuit contains all the hardware needed for both ESP8266#1 and ESP8266#2. As you can see, there are only a few components needed. It is probably wise to stick with this single hardware configuration for both ESP8266 setups.

However, once tested and all the remote codes have been “learned” and saved, the two ESP8266 systems could be optimized as follows.


IR Transmit LED, Send switch and Status LED could be removed. The only thing needed is the receive IR. Remember, a separate ESP8266#1 circuit can be used for each TV you wish to control with a single DVR box.


IR Receive LED, Send switch and Status LED could be removed. The only thing needed is the Tx IR. Only one of these circuits will be needed, regardless of how many remote TVs are used.

IR Remote Control Signals

There are many great articles that provide details on how IR signals are generated, transmitted, received and decoded. Instead of repeating, here are a few references for further reading, if you want to know more. This post will concentrate on an ESP8266 IR remote solution.

ESP8266 IR Test Software

My initial idea was to port an existing IRremote library from the proven Arduino platform to the ESP8266. The obvious choice was the “RobotRemote” library provided as a standard Arduino IDE library. But the differences in the ESP8266 hardware from the Arduino ATmega chip made the porting difficult.

Even after resolving all the compile errors, I could not complete a successful link to all the libraries. Eventually I ended up abandoning the Arduino IDE platform for this project in favor of the EspressIF SDK.

But this decision came with additional challenges as the SDK does not easily support c++ class libraries. Like the “RobotRemote” library. This issue was overcome by decomposing the class structure into separate ANSI C functions.

But there was more to deal with…

Remote IR Signal Generation

The Arduino library relies on the PWM capability to generate the standard 38 kHz IR modulation frequency. Unfortunately, the ESP8266 PWM API only supports up to 100 Hz, a far cry from the needed bandwidth.

Fortunately, there is a way around this ESP8266 constraint. The trick is to create the 38 kHz modulation by simply toggling a digital output; logic 1 and logic 0. The duration of these pulses determine the command sent to the remote receiver. But how do we generate 38 kHz pulses?


Using the ESP8266 micro-second delay statement “os_delay_us(us)”, we can create a 38 kHz pulse train. Each pulse period is 1/38000 seconds (26.3 us) long. Rounding that off to 26 us, the modulation frequency is easily achieved with:

  loops = time/26;                    // "time" units are microseconds
  if(loops==0) loops=1;
  for (i=0;i&lt;loops;i++) { 
          gpio_write(IR_SEND_PIN, 0); //Set GPIO12 LO -&gt; IR On
	  os_delay_us(13);  //1M/38K/2
	  gpio_write(IR_SEND_PIN, 1); //Set GPIO12 HI -&gt; IR Off
	  os_delay_us(13);  //1M/38K/2

Here, each iteration of the loops generates one 38kHz pulse (26 us). The number of pulses (loops) is determined by the desired number of microseconds.

Remote IR Signal Detection

In addition to generating IR codes, we must also be able to detect and decode IR signals received from a remote. That requires a sampling of the state of the IR detector diode (is it HI or LO). A 50 us timer callback function is implemented for this purpose, which is the same 20 kHz sampling frequency used by the original Arduino RobotRemote library. Since the 38 kHz modulation is removed by the IR detector, the remaining signal content (set of ones and zeroes) change at a lower rate. As result, the 50 us sample rate is adequate to accurately decode the incoming IR code.


Initial Implementation

My initial implementation provides a framework upon which to build an ESP8266 based IR remote application. It is not meant to be a complete application, merely a platform to prove the concept. From this structure, it will be possible to easily adapt the code for your specific needs. I plan to follow-up this post with my final design.

From the current structure, it will be a straightforward task to record and store all the IR remote codes for subsequent replay, on demand, by the ESP8266#2 web server.

Here is what this project currently does:

  1. With the push-button in the schematic open, the IR detector is monitored every 50 us for the presence of an IR code. Every time a logic state is detected  on this  sensor, the LED connected to GPIO16 is blinked. In addition, the received code is sent to the serial port. Once a valid code is detected, it is stored for playback, on-demand,  by the IR emitter diode.
  2. When the push-button in the schematic is pressed, the IR detection process is stopped and the last IR code store is transmitted. The code is repeated every 0.5 seconds as long as the button is pressed. IR detector sampling will resume once the button is no longer closed.

The code for this project is on Github here.

What to do next

Note that the IR codes sent to the serial output can be saved using any terminal program that saves the output to a file. By sequentially walking through each key on a remote, a map of button pressed to IR code can be created. This map will have 2 purposes in the final design:

  1. ESP8266#1:  The received code can be “looked up” in the map, to determine which remote key was pressed.
  2. ESP8266#2: Once the Web server receives a command to send a key code, the map will identify the code to send for that key.

The one shortcoming I have observed with this initial design is the limited range for both sending and receiving IR signals. Currently, the signal fades and starts to drop out beyond only 1 meter. This has one of two possible causes, which I intend to investigate.

Either the signal intensity is inadequate or the signal MARK/SPACE timing is off. We shall see.

I blew up a couple of IR Emitter Diodes using a transistor to increase the LED intensity. As results, a more thorough evaluation is needed before I proceed with additional modifications. I will provide additional information when a better solution is reached.


The project presented here provides a solid foundation for any ESP8266 application using IR communication. This design uses the EspressIf SDK but could most likely be adapted to work with the Arduino IDE. So that others may benefit, please post your work in the comments below if anyone has ported this to the ESP8266 Arduino IDE platform.

Hope you find this information useful…

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Mobile Weather Sensors Using ESP8266 – Phase 5: Ant+ Heart Rate Monitor

Adding a Heart Rate Monitor (HRM) wraps up the Mobile Weather Sensor project. To get started, a sensor selection was needed. And since I already have and use a Garmin HRM with a wireless chest sensor, using that same sensor with my setup was the logical choice.

But how to do it?

That was the challenge…

First thing was to figure out how the Garmin unit worked. What sort of RF signal was being sent to my handlebar mounted display? And what message protocol is used? What will it take to interface with my Android, wirelessly?

After some research, I found that the Garmin HRM used an Ant+ interface.

What’s that? Ant+ does look a bit intimidating at first glance. Take a look here.

Fortunately. I was able to boil things down to the bare essentials of what was needed in order for my android phone to receive heart rate data from the sensor. There were several elements needed to make things work…

  • An ant+ radio was needed in the smartphone
  • The ant+ API works directly with a native android app. But since the Weather Sensor App uses the Cordova web interface, a method of communication was needed between the Cordova JavaScript code and the native Java code.
  • The phone app needed to automatically detect the HRM and pair with it (like bluetooth).

These modifications to the existing android app integrate the Java Ant+ API, the Heart Rate Monitor and JavaScript.

The Phone Ant+ Radio

Fortunately, my Samsung Galaxy Note 3 has a built-in ant++ radio. But in order to access this interface, an App must be installed from the Google Play Store. It is called ANT+ Plugin Service. It is really simple. There is no App icon to launch. This is how it works…

Once installed, the service is called anytime an App attempts to connect with an ant+ device. My phone is an ancient model, almost two years old now. Many of the newer phone come with this service pre-installed.


JavaScript to Java Interface

With an interest in portability between android and iOS phones, the Mobile Weather Sensor App has been built with a standard web interface. This presented a problem since the API provided by the ANT+ team supports android native Java (.java files) but not JavaScript.hrm-code

Fortunately, a mechanism has been provided to “extend” the Cordova Web API to communicate with Java code. Here is the source of the information I used to implement the interface between my App and the native code needed to communicate with my heart rate monitor.

First thing to do was to add a reference to this interface code to the project’s config.xml file:

&lt;feature name="HeartRateMonitor"&gt;
       &lt;param name="android-package" value="org.apache.cordova.antplus.heartrate.HeartRateMonitorInterface" /&gt;
       &lt;param name="onload" value="true" /&gt;

The first parameter identifies the file containing the feature class object. In this case, the Java code is contained in the file “”. The second parameter makes this feature available upon loading the application’s Web view.

But how do we call the Java code from JavaScript?

Here is the Cordova mechanism used to call Java feature “actions” from JavaScript:

    callback-if-successful,    //JavaScript Callback function if call 
                               //to Java code was successful
    callback-if-error,         //JavaScript Callback function if call
                               //to Java code was not successful
    "feature name",            //Feature name from config.xml file.
    "feature action",          //Feature action to be executed from 
                               //the .java file
    ["parameter array"]);      //Parameter array to send to Java code

As we shall see, the Java code can return any string back to the JavaScript callback functions. That is how the heart rate received by the Java code is returned JavaScript.

Only two feature actions were implemented to support the heart rate monitor interface:

  1. ConnectHeartRateMonitor – This method establishes a connection between the App and the Heart Rate Monitor
  2. GetHeartRate – This method retrieves the newest heart rate from the Java code.

ConnectHeartRateMonitor is called once at the start of the application while GetHeartRate is called each time the app refreshes the sensor values.

The Java Code

The Java code implements the  class “HeartRateMonitorInterface”. This class contains the following key methods:

  1. execute – This required methods is executed when JavaScript “cordova.exec(()” is called. As noted above, this method only supports two actions.
    1. ConnectHeartRateMonitor makes a call to the Ant+ API method “.requestAccess”. Fortunately, the API does all the hard work of connecting to the Heart Rate Monitor. The Class callback “base_IPluginAccessResultReceiver.onResultReceived” methods is invoked to report the status of the call.
    2. GetHeartRate simply returns the latest heart rate value back to JavaScript.
  2. base_IPluginAccessResultReceiver.onResultReceived is the callback invoked when the ant+ “.requestAccess” method is called. If access was successfully granted, we subscribe to the Heart Rate Monitor Events. Whenever a new event is received, the callback “HeartRateDataReceiver().onNewHeartRateData()” is invoked.
  3. IHeartRateDataReceiver().onNewHeartRateData() receives updates from the heart rate. Upon receipt of a new sensor value, the heart rate is saved to a class variable for retrieval, on-demand, from the JavaScript.


We now have a working application that supports all of the capabilities planned. The Eclipse project files for this application are on GitHub here. The data collected on this mobile application include:

  1. Temperature
  2. Barometric Pressure
  3. Humidity
  4. Speed
  5. Direction
  6. Coordinates
  7. Heart Rate
  8. Altitude
  9. UTC timestamp
  10. Internal ESP statistics

Who knows, there may be more added…

I am looking forward to the coming change of season. With this App and the ESP sensors, I expect to collect some interesting information about significant changes in micro-climate in the span of short distances along the local mountain trails. It will be great to finally quantify what is felt externally as you must peel on and off layers of clothing with changing conditions.

I hope you have found this information is useful to you in your own projects…

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