Turning the Makey Makey Into a Capacitive Sensor

I bought a Makey Makey a few months ago and when I started playing with it, I realised quickly that having to attach one of the alligator clip to your wrist or finger to be able to use the device properly made the experience a bit less exciting for me.

What I really wanted was to be able to simply touch any conductive surface to create a reaction, without have to touch the other wire usually connected to the “earth” part of the board.

So I started looking for a solution to turn this board into a real capacitive sensor. At first I thought it would not be possible but, after looking for a few days, I finally found a solution.

So, if like me, you’d like to make your board do something different, follow the steps below:

• Plug a wire in the pin number 5 of the board.

• Plug your Makey Makey in your computer.

• Launch the Arduino IDE and in the “Board” section of the menu, select the Makey Makey.

• Copy and paste the following code:

    
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int capSensePin = 5;

// This value may be different.
int touchedCutoff = 0;

void setup(){
  Serial.begin(9600);
}

void loop(){

  if (readCapacitivePin(capSensePin) > touchedCutoff) {
    Serial.println(readCapacitivePin(capSensePin));
  }

}

uint8_t readCapacitivePin(int pinToMeasure){
  // This is how you declare a variable which
  // will hold the PORT, PIN, and DDR registers
  // on an AVR
  volatile uint8_t* port;
  volatile uint8_t* ddr;
  volatile uint8_t* pin;
  // Here we translate the input pin number from
  // Arduino pin number to the AVR PORT, PIN, DDR,
  // and which bit of those registers we care about.
  byte bitmask;
  if ((pinToMeasure >= 0) && (pinToMeasure <= 7)){
    port = &PORTD;
    ddr = &DDRD;
    bitmask = 1 << pinToMeasure;
    pin = &PIND;
  }
  if ((pinToMeasure > 7) && (pinToMeasure <= 13)){
    port = &PORTB;
    ddr = &DDRB;
    bitmask = 1 << (pinToMeasure - 8);
    pin = &PINB;
  }
  if ((pinToMeasure > 13) && (pinToMeasure <= 19)){
    port = &PORTC;
    ddr = &DDRC;
    bitmask = 1 << (pinToMeasure - 13);
    pin = &PINC;
  }
  // Discharge the pin first by setting it low and output
  *port &= ~(bitmask);
  *ddr |= bitmask;
  delay(1);
  // Make the pin an input WITHOUT the internal pull-up on
  *ddr &= ~(bitmask);
  // Now see how long the pin to get pulled up
  int cycles = 16000;
  for(int i = 0; i < cycles; i++){
    if (*pin & bitmask){
    cycles = i;
    break;
  }
}
// Discharge the pin again by setting it low and output
// It's important to leave the pins low if you want to
// be able to touch more than 1 sensor at a time - if
// the sensor is left pulled high, when you touch
// two sensors, your body will transfer the charge between
// sensors.
*port &= ~(bitmask);
*ddr |= bitmask;

return cycles;
}

• Upload the code onto the Makey Makey and open the serial monitor.

You should see the value 0 printed when you’re not in contact with the wire plugged in pin 5. If it changes to 1 when you’re touching it, then it’s working!

Now if you plug the wire in a conductive matter, you should be able to produce an effect by touching it without having to hold the cable plugged in the earth port of the board! :)

To get started, you could try to connect an Arduino with an LED and make it turn on when you’re touching the wire!

Hope it helps!