04 Communication

Create a small project that does the following:

  • Read at least two sensor values using Arduino. You can use any sensor you want to but they should be some other sensors than the ones we used in the class examples this week. They can also be two channels from the same sensor such as the X and Y of the accelerometer.
  • Print out the values using the Serial port in a way that you can separate the different values.
  • Create a small sketch using Processing or p5.js (or some other programming environment) to read the sensor values from the serial port. You can use the examples on this page as a starting point.
  • Map the sensor values to some parameters in your sketch. You can simply visualize the data in some way or create something more interesting and meaningful that is more connected to the interaction. Do something else than the example we created today.

I chose to work with the rotary dial mechanism and the idle switch of Matti’s red example telephone, because it is relevant for my final project. The idle switch is triggered when the handset is lifted or placed back on the telephone – basically like a simple button. For this reason I chose Arduino pin 2 to read its signal and added a 10k resistor to prevent a short circuit. The rotary-dial on the other hand was harder to figure out. Matti explained to me that the dial returns a number of pulse signals depending on the number dialled. He knew which wires were the correct ones to read the signal of his telephone’s dial (red and blue). To be sure we tested the signal with the multimeter. With the knowledge gained I connected the dial’s wires with the breadboard and I chose Arduino pin 9 to read its signal.

This video helped me a lot to understand the mechanism in detail and how to set up the code:https://www.youtube.com/watch?v=cZ2rHqBXO1s&ab_channel=PlayfulTechnology

In this process I learned how to use the bounce library that helps to prevent signal noise. The main idea of the code is to swich between two states: idle and dial. Idle is the state when the handset is placed on the telephone. Dial is the state when the handset is lifted and the user can dial in a number. By placing the handset back on the telephone (or by simply pressing the switch) the user can confirm the last dialled number. This number will be printed out in the console. I then set up a code in processing that communicates with the Arduino and visualizes the dialled number as a bigger graphic.

I uploaded the first version of my code onto the Arduino but unfortunately nothing happened. I couldn’t fin the mistakes by myself, so I asked help from my fellow student Aditya (https://troublebydesign.com/). With his help I made changes of the order of things to happen in my Arduino code. Another try, another failure. Aditya then took a close look at my circuit and found that the idle switch was not properly connected. The red wire was supposed to be connected to the 5V power source coming from the Arduino, but instead I accidentally connected it to ground where I already had a connection – ergo: no current flow. After I fixed that, everything worked fine.

Arduino Code

// For handling software debouncing of mechanical switch contacts
#include <Bounce2.h>

// Pins
int idlePin = 2;  // Handset
int dialPin = 9;  // Rotary-dial

// States
int state = 0;

// How many pulses have been detected for the dialled digit
int pulseCount = 0;

// Bounce objects
Bounce idleSwitch = Bounce();
Bounce dialSwitch = Bounce();

void setup() {
  // Open the serial port
  // Declare pin inputs and attach debounce ojects
  pinMode(idlePin, INPUT);
  pinMode(dialPin, INPUT);

void loop() {
  // Read the current state of all switches

  switch (state) {
    // Idle
    case 0:
      if (idleSwitch.rose()) {
        state = 1;

    // Dial
    case 1:
      if (dialSwitch.rose()) {
        // The digit 0 has 10 pulses
        if (pulseCount == 10) {
          pulseCount = 0;

  // If the handset is placed on the telephone, the telephone becomes idle (no matter when)
  if (idleSwitch.fell()) {
    state = 0;
    pulseCount = 0;

Processing Code

import processing.serial.*;

Serial myPort;  // Create object from Serial class
String str;      // Data received from the serial port

void setup()
  size(500, 500);
  // Open whatever port is the one you're using.
  // Change the 0 in  Serial.list()[0] to the correct device
  String portName = Serial.list()[0];
  myPort = new Serial(this, portName, 9600);

void draw()
  if ( myPort.available() > 0) { // If data is available,
    str = myPort.readStringUntil('\n'); // read it and store it in str
    if (str != null) {
      textAlign(CENTER, CENTER);
      text(str, width/2, height);

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