Here’s a radical idea: Put down that PSP for a while. Give your tired fingers a break from its complex configurations of buttons and action controls, and try a whole different kind of game machine, one that uses just a single button and can be built and modified at home. At the core of this simple yet elegant retro game platform is a device called a ScreenKey, a small LCD screen built on top of a pushbutton. Couple it with a tiny programmable microcontroller, and you have a complete portable DIY “GameKey” system. (We housed ours in a small candy container.) It may not replace your Nintendo DS, but it can run most any basic game you can create for it. We’ve even written one already to get you started: Red Fish, Green Fish, Blue Fish—SHARK! [see below]. Kids’ll love it. Just assemble the parts, download our code here to program the microcontroller, and put your game face on.

See to get a list of AVR programmers, which convert the game code so the microcontroller can read it. Also see PopSci’s past AVR-related articles and how-to pieces at


Time: 2 hours
Cost: $71.89
Difficulty: Moderate

  1. Download our code here and transfer it to the microcontroller using an AVR programmer.
  2. Download the data sheets, which contain connection instructions for the ScreenKey ( and the microcontroller (
  3. Wire the data, clock and switch pins for the ScreenKey to the microcontroller and its power pins to the DC-to-DC step-up. Add resistors, which ensure that the signal levels to the ScreenKey’s pins are stable.
  4. Insert an AA battery, and slide the whole assembly into your preferred container. Move the jumper switch on the battery compartment to turn on your GameKey. Spend the rest of your day staring into the button screen.

Inside the Gamekey

The simple hardware behind the Gamekey consists of a ScreenKey display panel, a DC-to-DC step-up board, a few resistors and a microcontroller.

The Rules of the Game

In Red Fish, Green Fish, Blue Fish—SHARK!, the ScreenKey displays bit-mapped images of aquatic life. When a fishy figure appears, press the button. But don’t press it when you see the shark—that means game over. The further you go, the faster the images will flash on the screen and the harder it will get.