What can you make using the circuit from a blinky greeting card, a clear plastic antiperspirant container, and 8 switches? Mystery Electronic Switches: A great prank project that taps the qualities of magnetic reed switches.
From maker Jeff Tregre’s intro:
Everyone loves a good mystery. Give someone this nifty magic gadget and tell them there’s a way to toggle the switches that will make its LEDs light up. No matter who else tries it, or how long they keep toggling the switches, the LEDs will never light up — until you do it.
Spoiler Alert: A good illusionist never discloses the secret that makes a trick work. Once you do, the magic has ended. With that said, I’ll break the magician’s code and reveal how the circuit works: inside the container are two reed switches that can be activated by a magnet. You wear a special magnetic ring that activates them. To show off your unique ability to make the LEDs light up, you just hold your finger with the magnetic ring alongside one of the reed switches. This project only took two evenings to design, build, and test.
When you’ve got it all wired up, let the magic begin. With the magnetic ring on, the only trick is that the switches at either end must be toggled in opposite directions from each other. The middle switch isn’t used at all; it’s just there, all wired up for show. Here are Jeff’s suggestions for a successful performance:
Practice your performance; the more confident you are, the more your audience will be determined to beat you at your own trick. Never display your trick to the same people more than 2 or 3 times, because someone will figure it out and reveal your secret. I tell my audience it’s a mathematical algorithm and only I know the sequence to toggle the 3 switches, then I dare them to match my ability to get the LEDs to light up. “Well, do you feel lucky?”