Making two Arduinos/MKR1000s communicate

Question

I am trying to create a project in my free time just for a bit of fun. It consists of two MKR1000s (one acting as a web server connected to one laptop, and the other acting as a web client connected to a different laptop - so I can view the Serial Monitor).

One MKR1000 has a potentiometer attached to it (therefore I can change the value of it), and sends the potentiometer value to the serial monitor every 4 seconds.

THE AIM: Once the web server sets up the w WifFi network, and the web client connects to that WiFi network, I want to send the potentiometer value across to the web client every time it gets updated. However, I am clueless on how to achieve this.

This is my web server void loop code (the rest is similar to the https://www.arduino.cc/en/Tutorial/Wifi101WiFiWebServer):

void loop() {
  WiFiClient client = server.available();
  // listen for incoming clients
  if (client) {
    // if you get a client,
    Serial.println("new client");
    // print a message out the serial port
    String currentLine = "";
    // make a String to hold incoming data from the client
    while (client.connected()) {
      // loop while the client's connected
      if (client.available()) {
        // if there's bytes to read from the client,
        char c = client.read();
        // read a byte, then
        Serial.write(c);
        // print it out the serial monitor
        if (c == '\n') {
          if (currentLine.length() == 0) {
            client.println("HTTP/1.1 200 OK");
            client.println("Content-type:text/html");
            client.println();
            // the content of the HTTP response follows the header:
            client.print("Click <a href=\"/showValue\">here</a> showValue of the potentiometer <br>");
            // The HTTP response ends with another blank line:
            client.println();
            // break out of the while loop:
            break;
          } else {
            // if you got a newline, then clear currentLine:
            currentLine = "";
          }
        } else if (c != '\r') {
          currentLine += c;
          // add it to the end of the currentLine
        }
        if (currentLine.endsWith("GET /showValue")) {
          Serial.println(sensorValue);
          delay(2000);
        }
      }
    }
    client.stop();
  }
}

And this is my web client code I use this https://www.arduino.cc/en/Tutorial/Wifi101WiFiWebClient - I am not sure how I should modify this in order to receive the potentiometer value across from the web server MKR1000. Any tips or hints would be hugely appreciated!

I am sorry if this is a simple question, however I am just starting with the Arduino idea, and I'm new to coding!

Answer 1

At the bottom of the page for the client code link you provided, there's a link to a Chat Server example. If you study the code I think you'll see how to send and receive the potentiometer reading. Hint: Look in the code where it echoes what it receives.

mkr1000 WiFi Chat Server

Answer 2

You don't have to use a webserver/webclient for this; a raw socket would also work. If you do want to use "web technology":

You can either have the webclient poll the webserver periodically for a new value (ask for a new value every few seconds, and interpret the response), or have the webserver initiate the communication every time a new value is available.

For the latter, you could use Server-Sent Events (SSE) or a Websocket, both of which are very google-able.

I have made examples for both, but these examples are fairly large and have extra functionality. Still, they may give you some pointers and/or code to reuse.

These examples are here:

https://github.com/ocrdu/arduino-webinterface-sse

and here:

https://github.com/ocrdu/arduino-webinterface-websocket-ap

Note that the client side in the examples is a webpage in a webbrowser, but the principle is the same.