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Create the Arduino Sketch

Arduino programs are called sketches, and represent a Javascript-like language for developing on that platform. In order to make our Max-to-Arduino connection work, we need to make a new sketch, and load it onto the Arduino device. The sketch we will use is as follows:

// Simple Max-Connection Sketch
// by Darwin Grosse for Cycling '74
// Note: This sketch uses simple coding - rather than efficient coding. No attempt is made to be clever - rather,
// the goal is to make a sketch that will be easy for people to modify regardless of experience level.
// --------------------------------------------------------------------------------------------------------------

// variable setup
int incoming;             // this is where we will store incoming serial data
int last_analog = -1;  // we start with a negative number so that the first reading will give us a new value!

// the setup part of the sketch
void setup() {
  // we need to set up the serial port for communication with the computer
  // we need to set up the four digital pins for output. We will also flash the lights to show we have
  // a good program. 
  for (int i=2; i<=5; i++) {     // scan through pins 2-5
    pinMode(i, OUTPUT);    // set the pin for OUTPUT
    digitalWrite(i, HIGH);      // turn the pin ON
    delay(500);                     // wait a half-second
    digitalWrite(i, LOW);       // turn the pin OFF
    delay(500);                     // wait another half-second
}  // end of setup

// the loop part of the sketch
void loop() {
  // This is where we take data coming from the computer and use it to turn on the LEDs
  // ----------------------------------------------------------------------------------
  if (Serial.available() > 0) {     // if we have incoming data from the computer...
    incoming =;    // get one byte from the serial port
    switch (incoming) {
      case 0:                    // if the byte is 0
        digitalWrite(2, LOW);    // turn off pin 2
      case 1:                    // if the byte is 1
        digitalWrite(2, HIGH);   // turn on pin 2
      case 2:                    // if the byte is 2
        digitalWrite(3, LOW);    // turn off pin 3
      case 3:                    // if the byte is 3
        digitalWrite(3, HIGH);   // turn on pin 3
      case 4:                    // if the byte is 4
        digitalWrite(4, LOW);    // turn off pin 4
      case 5:                    // if the byte is 5
        digitalWrite(4, HIGH);   // turn on pin 4
      case 6:                    // if the byte is 6
        digitalWrite(5, LOW);    // turn off pin 5
      case 7:                    // if the byte is 7
        digitalWrite(5, HIGH);   // turn on pin 5
  }  // end of if for Serial.available()
  // This is where is check the current value of the potentiometer, and send the value if it has changed.
  // ----------------------------------------------------------------------------------------------------
  incoming = analogRead(0);      // get the current value of the control
  incoming >> 4;                         // strip the 3 lowest bits - to prevent jitter, and to put the value
                                                   // in the typical MIDI range of 0 - 127
  if (incoming != last_analog) {   // make sure it has changed...
    Serial.write(incoming);           // send the byte to the computer
    last_analog = incoming;        // save the new data
  }  // end of if values have changed
} // end of loop()

A few things to notice. First, we are using the following data to turn on and off the LEDs:

pin value for off value for on
pin 2 0 1
pin 3 2 3
pin 4 4 5
pin 5 6 7

This is a pretty easy protocol to follow, and will be easy to implement in Max code. Conversely, in order to make the data coming into Max easy to use, we change the analog read value to be in the range of 0-127. This way, it "looks" like MIDI data, and will fit in easily within our patching environment.

Now the Arduino is all set up, and it's time to dive into making a Max patch.

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