🍌🎹 Banana piano

core.clj

(ns musikk.core
  (:require [serial-port :as serial]
            [overtone.live :refer :all]
            [overtone.inst.sampled-piano :refer :all]))

(def port (serial/open "/dev/tty.usbserial-A800F185" 57600))

(defn chr->int [c]
  (-> (char c)
      (str)
      (Integer.)))

(defn handle-press [input]
  (let [idx   (chr->int input)
        scale (scale :C3 :major)
        note  (nth scale idx)]
    (sampled-piano note)))

(serial/remove-listener port)
(serial/on-byte port handle-press)

mcu.ino

const int PORTS[8] = { 2, 3, 4, 5, 6, 7, 8, 9 };
const int THRESHOLDS[8] = { 7, 7, 7, 7, 7, 7, 7, 7 };

bool touched[8];

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);
  // Prevent the timer IRQ from disturbing our measurement
  noInterrupts();
  // Make the pin an input with the internal pull-up on
  *ddr &= ~(bitmask);
  *port |= bitmask;

  // Now see how long 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;}

  // End of timing-critical section
  interrupts();

  // 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;
}

void setup() {
  Serial.begin(57600);
}

void handlePort(int index) {
  int cycles = readCapacitivePin(PORTS[index]);
  
  if (!touched[index] && cycles >= THRESHOLDS[index]) {
    touched[index] = true;
    Serial.print(index);   
  }
  
  if (touched[index] && cycles < THRESHOLDS[index]) {
    touched[index] = false;
  }
}

void loop() {
  for (int i = 0; i < 8; i++) {
    handlePort(i);
    delay(10); // cheap-ass debounce..
  }
}