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.