This board connects to an 8-bit 5V bus and converts the digital bus value to seven segment hexadecimal display in software on the microcontroller. On my Arduino, the software is // The lookup table converts the four-bit input to the seven segment display. The MSB is segment a and the LSB is segment f. char lookup_table[16] = {0x7E, 0x30, 0x6D, 0x79, 0x33, 0x5B, 0x5F, 0x70, 0x7F, 0x7B, 0x77, 0x1F, 0x0D, 0x3D, 0x4F, 0x47}; void setup() { DDRB = B00000000; // 8 bit input (digit 1 high nybble, digit 2 low nybble) PORTB = B11111111; // With pull up resistors DDRD = B11111111; // Outputs for digit 1 (a-f MSB to LSB) and segment a digit 2 (LSB) DDRC = B00111111; // Remaining 6 segments of digit 2 (b-f) } void loop() { int digit1_in = (PINB & 0xF0) >> 4; int digit2_in = (PINB & 0x0F); int digit2_segments = lookup_table[digit2_in]; PORTD = (lookup_table[digit1_in] << 1 & 0xFE) + ((digit2_segments & 0x7F) >> 6); PORTC = digit2_segments & 0x3F; }