Color Image Budapest 8 by 8 LED display driver

Building and burning the firmware

Dependencies: make gcc-avr avrdude

make program

If you haven't changed the clock settings to 8 MHz and no clock divider, you'll also need to run make burn-fuse

Protocol

One-way communication is done in 1 byte serial (USART) packets @ 9600 bps:

(MSB) RRRS PPPP (LSB)

• 3 bits for row selection (0-7, 0 is the topmost)
• 1 bit for side selection (0 is left, 1 is right)
• 4 bits pixel payload (LSB is the rightmost)

Examples

(dots represent unchanged pixels)

Packet: 01001011 (0x4b)

Display:

. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
x   x x . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .

Packet: 11111111 (0xff)

Display:

. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . . . . .
. . . . x x x x

Controller board

• ATtiny2313 microcontroller running at 8 MHz (internal clock)
  • PORT B (PB0-PB1) for column addressing with a shift register
  • PORT D (PD2-PD5) for row addressing
• 74HC138 3 to 8-line demux (row selection)
• 74HC164 8 bit serial-in parallel-out shift register (column buffer)
• transistors for driving

Schematics

Display board layout

• 5 LEDs are in series for each pixel
• rows are numbered from top to bottom
• cols are numbered from right to left
• right and left are referred to as when looking at the LEDs
• row pins must be positive, col pins must be grounded for LEDs to light

ASCII art layout:

.------------------------------.
|        COLOR  IMAGE    (TOP) |
|          BUDAPEST            |
|                              |
|          ++++++++ (row pins) |
|                              |
|                              |
|                              |
|                              |
|          ........ (blank)    |
|                              |
|                              |
|          ++++++++ (col pins) |
|                              |
| (RIGHT)   (back)      (LEFT) |
'------------------------------'