Arduino Example for Keypad (36 buttons 6x6 matrix)

keypad.cpp

#include <Arduino.h>

#define BUTTON_COUNT 36
#define KEYPAD_OUTPUT_BEGIN 2
#define KEYPAD_OUTPUT_END 7
#define KEYPAD_INPUT_BEGIN 8
#define KEYPAD_INPUT_END 13


uint8_t keypad_button_pressed[BUTTON_COUNT];
volatile uint32_t ticks;
uint32_t lastTrigger;


ISR(TIMER0_COMPA_vect, ISR_BLOCK) {
	ticks++;
}

void init_systicks() {

	TCCR0B = _BV(CS02) | _BV(CS00);
	TCCR0A = _BV(WGM01);
	TIMSK0 = _BV(OCIE0A);

	// 8000000/1024/78 == 100HZ -> 10 ms
	OCR0A = 77; // !!! must me set last or it will not work!
}

uint32_t math_calc_diff(uint32_t value1, uint32_t value2) {
	if (value1 == value2) {
		return 0;
	}
	if (value1 > value2) {
		return (value1 - value2);
	}
	else {
		// check for overflow
		return (0xffffffff - value2 + value1);
	}
}

void keypad_reset_output() {
	// configure pull ups
	digitalWrite(2, HIGH);
	digitalWrite(3, HIGH);
	digitalWrite(4, HIGH);
	digitalWrite(5, HIGH);
	digitalWrite(6, HIGH);
	digitalWrite(7, HIGH);
}

void clear_buttons() {
	for(int i=0; i < BUTTON_COUNT; i++) {
		keypad_button_pressed[i] = 0;
	}
}

void keypad_setup() {
	// initialize the digital pin as an output:
	pinMode(2, OUTPUT);
	pinMode(3, OUTPUT);
	pinMode(4, OUTPUT);
	pinMode(5, OUTPUT);
	pinMode(6, OUTPUT);
	pinMode(7, OUTPUT);

	keypad_reset_output();

	pinMode(8, INPUT);
	pinMode(9, INPUT);
	pinMode(10, INPUT);
	pinMode(11, INPUT);
	pinMode(12, INPUT);
	pinMode(13, INPUT);

	// configure pull ups
	digitalWrite(8, HIGH);
	digitalWrite(9, HIGH);
	digitalWrite(10, HIGH);
	digitalWrite(11, HIGH);
	digitalWrite(12, HIGH);
	digitalWrite(13, HIGH);
}



// the loop() method runs over and over again,
// as long as the Arduino has power

void keypad_read_buttons() {
	clear_buttons();
	uint8_t y=0;
	for(int i=KEYPAD_OUTPUT_BEGIN; i <= KEYPAD_OUTPUT_END; i++) {
		keypad_reset_output();
		digitalWrite(i, LOW);
		uint8_t x=0;
		for(int j=KEYPAD_INPUT_BEGIN; j <= KEYPAD_INPUT_END; j++) {
			if (digitalRead(j) == LOW) {
				uint8_t index = x+6*y;
				keypad_button_pressed[index] = 1;
			}
			x++;
		}
		y++;
	}
}

uint8_t keypad_button_is_pressed() {
	for (int i=0; i < BUTTON_COUNT; i++) {
		if (keypad_button_pressed[i]) {
			return 1;
		}
	}
	return 0; // no button pressed
}

// The setup() method runs once, when the sketch starts
void setup() {
	init_systicks();
	keypad_setup();

	Serial.begin(9600);
}

void loop() {

	keypad_read_buttons();

	// allow button processing only every 300ms (30 systicks)
	if (keypad_button_is_pressed() && (math_calc_diff(ticks, lastTrigger) > 30)) {
		lastTrigger = ticks;

		for(int i=0; i < BUTTON_COUNT; i++) {
			if (keypad_button_pressed[i]) {
				Serial.print(i);
				Serial.print(' ');
			}
		}
		Serial.println('-');
	}

	delay(1);
}

int main(void) {

	init();
	setup();

	while (true) {
		loop();
	}
}