Blind attempt at controlling the frequency of a 555 timer

synth.c

int pin = 0; // The pin we will read the audio signal from

volatile int last = 0; // The time of the last sample
volatile int expected = 2272; // Roughly 440Hz
volatile int data = 0; // The direction to change the digi-pot

void setup() {
	pinMode(pin, INPUT);
	last = micros();
	attachInterrupt(0, adjust, FALLING);
}

void loop() {
	// TODO: On midi input change the expected time
}

void adjust() {
	int elapsed = micros() - last;
	last += elapsed;
	
	if (elapsed > expected) {
		data = 1;
	} else {
		data = 0;
	}

	// TODO: Clock the digi-pot
}