Hello again!

This time I'm writing to show you my newest electronic creation: a "videogame console" made with a PIC18F2550 as its brain. It has a 8x16 LED matrix as main display and 4 seven segment displays to show the player score, for example. It has 8 buttons (4 in a pad, the rest like a Game Boy or similar). The PIC doesn't have enough pins to control everything easily, so I've used a few 74HC595 to control the LED matrix and the seven segment displays, and a 74HC166 to read the state of all buttons.

Photo of the front of the board Photo of the back of the board

The game I've decided to code for the demonstration is a simple Tetris, written in 100% assembly. YouTube video here:



  • Move left/right.
  • Rotate clockwise/counterclockwise.
  • Go down quickly, go down instantly.
  • Pause, reset.

At the moment I haven't decided if I should post the schematics and the source code for various reasons:

  • I used different systems to power the LED matrix and the seven segment displays. A decent design should use the same system.
  • Some resistors are too high and the LEDs, when lit, are too dim. I didn't consider the scanline refresh when calculating the resistors, so the actual intensity is a lot lower than I thought.
  • The source code of the game is a bit messy (the "drivers" code is good, though).

Well, I hope you like it!

EDIT: Well, whatever, I'll just put the schematics and the code... :P


Schematics in color

Schematics in black and white


Don't expect it to be clean and/or human readable. The file 'main.asm' contains the 'drivers', and 'tetris.asm' contains the game. It's fairly easy to modify it to change some of the pin assignments.

Download (gEDA schematics + assembly code + assembled .hex file)

New version (2015/10/06), with a small modification to prevent "ghosting" between displays when performing the scanline change. Also fixed a bug that didn't remove completed lines before checking if game over.


Possible improvements

  • Change pull-down resistors for the buttons (R29-R36) by 10K resistors.
  • Change LED resistors (330 Ohm) by 300 or maybe 220 resistors (R1-R16 and R37-R44).
  • Make the LED matrix and the seven segment displays work the same way (changing the displays by common-anode equivalents and the transistors used to drive them).