// This code consists of a procedure called readCapacitivePin // The procedure takes one input: an Arduino pin number // The procedure outputs: a number, from 0 to 17, which // indicates how much capacitance is on the pin. // When you touch the pin, or anything attached // to the pin, the number will get higher #include "pins_arduino.h" // Arduino pre-1.0 needs this uint8_t readCapacitivePin (int pinToMeasure) { // Variables used to translate from Arduino to AVR pin naming 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; port = portOutputRegister(digitalPinToPort(pinToMeasure)); ddr = portModeRegister(digitalPinToPort(pinToMeasure)); bitmask = digitalPinToBitMask(pinToMeasure); pin = portInputRegister(digitalPinToPort(pinToMeasure)); // Discharge the pin first by setting it low and output *port &= ~(bitmask); *ddr |= bitmask; delay(1); // Make the pin an input with the internal pull-up on *ddr &= ~(bitmask); *port |= bitmask; // Now see how long it takes for the pin to get pulled up. // This manual unrolling of the loop // decreases the number of hardware cycles between each read of the pin, // thus increasing sensitivity. uint8_t cycles = 17; if (*pin & bitmask) { cycles = 0;} else if (*pin & bitmask) { cycles = 1;} else if (*pin & bitmask) { cycles = 2;} else if (*pin & bitmask) { cycles = 3;} else if (*pin & bitmask) { cycles = 4;} else if (*pin & bitmask) { cycles = 5;} else if (*pin & bitmask) { cycles = 6;} else if (*pin & bitmask) { cycles = 7;} else if (*pin & bitmask) { cycles = 8;} else if (*pin & bitmask) { cycles = 9;} else if (*pin & bitmask) { cycles = 10;} else if (*pin & bitmask) { cycles = 11;} else if (*pin & bitmask) { cycles = 12;} else if (*pin & bitmask) { cycles = 13;} else if (*pin & bitmask) { cycles = 14;} else if (*pin & bitmask) { cycles = 15;} else if (*pin & bitmask) { cycles = 16;} // Discharge the pin again by setting it low and setting // it to be an 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; } int key1 = 6; // name of the first sensor key int touchValue; // will store sensor readings void setup() { pinMode(key1, INPUT); // set key1 to be an input Serial.begin(9600); // initialize the communication } void loop() { touchValue = readCapacitivePin(key1); // read the touch sensor value Serial.println(touchValue); // send touchValue to the computer if (touchValue > 4) { tone(3, 659, 100); // play tone 60 (C5 = 523 Hz) } delay(100); // delay for 1/10 of a second }