arduino digit display

// HIGH and LOW are aliases for 1 and 0 respectively
// each of these uses only 1 byte of memory

const unsigned char digit_bits[] = {
    0b11111100  // 0
    0b01100000, // 1
    0b11011010, // 2
    0b11110010, // 3
    0b01100110, // 4
    0b10110110, // 5
    0b10111110, // 6
    0b11100000, // 7
    0b11111110, // 8
    0b11110110, // 9
// you could have bit patterns for other digits after this, such as hexadecimal
};

void display_digit( int which_digit, int number ) {
    unsigned char bits;
    digitalWrite( which_digit, HIGH );

    bits = ~digit_bits[ number ];
    // flip all the bits, since 0 means the segment is on apparently
    // this could also overrun the array and show garbage, but that's the fun part

    // write the bits out backwards, so that the definitions are more readable
    digitalWrite( SEG_DOT, bits & 1 ); bits >>= 1;
    digitalWrite( SEG_G,   bits & 1 ); bits >>= 1;
    digitalWrite( SEG_F,   bits & 1 ); bits >>= 1;
    digitalWrite( SEG_E,   bits & 1 ); bits >>= 1;
    digitalWrite( SEG_D,   bits & 1 ); bits >>= 1;
    digitalWrite( SEG_C,   bits & 1 ); bits >>= 1;
    digitalWrite( SEG_B,   bits & 1 ); bits >>= 1;
    digitalWrite( SEG_A,   bits );

    delay( GHOST_DELAY );
    digitalWrite( which_digit, LOW );
}