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The Egyptian Coin Box ‘Trick’ [Hackaday]
[James Stanley] likes to spend time making puzzles and gadgets for escape rooms, and decided for a change to try their hand at a bit of magic. The idea was to construct a ‘magic box’, in which a coin can be placed in one of a number of slots, and then be able to remotely be able to determine the slot by means unseen. Obviously, this is an electronics hack, with a neat package of sensor and radio comms hidden inside a stack of CNC-milled wood. Coin locations are transmitted via Bluetooth to a Bangle.js smartwatch, which vibrates according to the slot occupied, allowing [James] to predict where the coin was placed.
 100vw, 400px”>The sensor uses capacitive sensing, with a plate below each coin slot acting as one electrode of a capacitor and a copper-clad board hidden in the upper plate acting as the second. The presence of a coin is detected as a change in the capacitance of one of the sensors due to the fact that the plate separation will now be less for that one position. A simple PCB was CNC routed from a piece of plain clad board, with a cut out to solder down a Seeed Studio XIAO-ESP32-C3 module which runs the show and provides Bluetooth connectivity via an external PCB antenna module. Handily this module also handles the lithium battery management.</p>
<p>The software stack seems to be Arduino, with a very simple capacitance testing routine based on measuring charge times. Overall this is very nicely executed, even if [James] reckons there’s a bit more to being a show magician than just being able to construct the hardware. Magical hacks are a bit of a rarity around these parts, but we found a couple, like this <a href=)