Suppose you wanted to build electronic dice for a board game. Sure, you could use discrete components to build a clock circuit into a decade counter and BCD to 7-segment decoder, etc. Or you could write some random number generating code for an Arduino and use LEDs. That’s obvious and has been done before. But professional toy inventors have to be crazy clever and get the same effect, but for an insanely low, dirt-cheap cost. Can you do it?

Here’s one approach that costs next to nothing: It’s just LEDs wired up with some cleverly designed SPDT switches. Each switch is made of three parallel wires and a metal ball in a cage. When you shake the cage, the ball randomly lands on either one pair of wires or the other pair. Only one pair of wires completes the circuit, lighting the LED.


To make an electronic die, I’d wire up 4 LEDs to one switch, 2 LEDs to the next switch, and a single LED to the last switch. Shake them all together and you’ll get a random number of LEDs to light up, from 0 to 7. For games that need a number from 1 to 6, just “roll” again if you get 0 or 7 lit LEDs.

Your challenge: Can you rewire the switches so that you’ll only get numbers 1 thru 6 — so that “0” and “7” never appear? Here’s a blank for you to draw your wires. (Hint: the new version may not be a “fair” die, but its average roll yield will be the same as a real die.)

Click here to download the solution to the challenge.





Step #1: Drill holes.

Super-Cheap Electronic Dice ChallengeSuper-Cheap Electronic Dice ChallengeSuper-Cheap Electronic Dice ChallengeSuper-Cheap Electronic Dice Challenge

Make a ball cage from acrylic by drilling three large through holes and then 3 small holes at 90 degrees. Drill holes for LEDs in the small panel.

Step #2: Complete the ball cage.

Super-Cheap Electronic Dice Challenge

Strip the heavy gauge solid core wire, cut into pieces and thread into the small holes, and super glue the ends to stack in place.

Step #3: Assemble the switch and LEDs.

Super-Cheap Electronic Dice Challenge

Solvent bond the switch to support and wire up the switches and LEDs: Click here to download the solution to the challenge.

Step #4: Assemble.

Super-Cheap Electronic Dice ChallengeSuper-Cheap Electronic Dice ChallengeSuper-Cheap Electronic Dice Challenge

Assemble and solvent bond the sub assembly.

Fit to cube (cut a hole in back for an on/off switch). Test!

Step #5: Finish (optional).

Super-Cheap Electronic Dice Challenge

For a more polished look, paint the cube white.

Leave the top clear, and add a piece of frosted mylar for a backlit look.

Bob Knetzger

Bob Knetzger

Bob Knetzger ([email protected]) is an inventor/designer with 30 years of experience making fun stuff.

  • Ben Hobby

    CAN I USE A TRANSISTOR??? I have a perfect design that only gives 6 outputs, 1-6 and works perfectly. It uses one NPN Transistor in the circuit, other than that just wires and leds. IS THAT CHEATING?

  • Sami Silvennoinen

    There’s a simpler solution for the 1-6 die, using even fewer LEDs: Make the initial wiring like given on this page for the 0-7 die, but remove one LED from the 4 LED set, so that you then have sets of 1, 2 and 3 LEDs. Then add one additional wire to connect the NC from the rightmost switch (i.e., the switch connected to 1 LED) to the 2 LED set, and you’re done. Average is 3.5 like in the solution given in the pdf.