keyboard.ino

#define USE_TIMER_3 true

#include <TimerInterrupt.h>
#include <ISR_Timer.h>

#include <Keyboard.h>

#define TIMER_INTERVAL_MS 5

#define num_rows 8
#define num_cols 9

int rows[num_rows] = {21, 20, 19, 18, 15, 14, 16, 10   };
int cols[num_cols] = { 0,  1,  2,  3,  4,  5,  6,  7, 8};

char charmap[72] = {
    /*      0    1    2    3     4    5                6              7       8 */
    /* 0 */ 'z', 'a', 'q', 'o',  '1', '9',             ' ',           KEY_F1, KEY_LEFT_SHIFT,
    /* 1 */ 'x', 's', 'w', 'p',  '2', '0',             KEY_BACKSPACE, KEY_F2, KEY_LEFT_CTRL,
    /* 2 */ 'c', 'd', 'e', ']',  '3', '-',             ' ',           KEY_F3, ' ',
    /* 3 */ 'v', 'f', 'r', ';',  '4', '=',             KEY_ESC,       KEY_F4, ' ',
    /* 4 */ 'b', 'g', 't', '\'', '5', KEY_DOWN_ARROW,  ' ',           KEY_F5, ' ',
    /* 5 */ 'n', 'h', 'y', ',',  '6', KEY_UP_ARROW,    ' ',           KEY_F6, ' ',
    /* 6 */ 'm', 'j', 'u', '.',  '7', KEY_LEFT_ARROW,  ' ',           KEY_F7, ' ',
    /* 7 */ 'l', 'k', 'i', '/',  '8', KEY_RIGHT_ARROW, KEY_RETURN,    KEY_F8, ' ',
};

void timerHandler(void)
{
    static int last_keys[num_rows * num_cols] = { 0 };
    static int next_keys[num_rows * num_cols] = { 0 };

    for (int c = 0; c < num_cols; c++)
    {
        digitalWrite(cols[c], LOW);

        for (int r = 0; r < num_rows; r++)
        {
            if (digitalRead(rows[r]) == LOW)
            {
                int idx = r * num_cols + c;
                next_keys[idx] = 1;
                Serial.print(r);
                Serial.print(",");
                Serial.print(c);
                Serial.print("\n");
            }
        }

        digitalWrite(cols[c], HIGH);
    }

    for (int i = 0; i < num_rows * num_cols; i++)
    {
        char key = charmap[i];

        // press if key is held down for two frames
        if (next_keys[i] && last_keys[i])
        {
            Keyboard.press(key);
        }
        
        // release
        else if (!next_keys[i] && last_keys[i])
        {
            Keyboard.release(key);
        }

        last_keys[i] = next_keys[i];
        next_keys[i] = 0;
    }
}

void setup()
{
    // initialize keyboard library
    Keyboard.begin();

    // pull all columns high
    for (int i = 0; i < num_cols; i++)
    {
        pinMode(cols[i], OUTPUT);
        digitalWrite(cols[i], HIGH);
    }

    // enable internal pull-up for all rows
    for (int i = 0; i < num_rows; i++)
    {
        pinMode(rows[i], INPUT_PULLUP);
    }

    ITimer3.init();
    ITimer3.attachInterruptInterval(TIMER_INTERVAL_MS, timerHandler);
}

void loop()
{
}