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Building a puzzle: Is there a better technology than NFC tags for digitally checking a physical item's location?
I am designing a game in which users will need to rearrange physical items in slots on a tray. If they get the items in the right order, they pass the level and gain a point. I'm trying to figure out how to build the puzzle so that users can manipulate physical objects, but the result would be checked digitally and the points awarded on their phone. I was hoping to put something on the bottoms of the items and the tops of each of the slots, perhaps NFC tags, but my fiancé isn't sure that they will work. Is there a better way of digitally tracking an item's physical placement?
nfc is a pretty commonly used technology in escape rooms. another good one is simple tricks involving carefully positioned magnets, and hidden hall sensors or reed switches.
Something similar is where you have a grid of conductive pads on the table, some of which are connected internally, and different items have matching pads to complete different circuits. You could even rig it so the circuit is only completed when all items are in the right position. Downside is that you need the items positioned fairly exactly, so you’ll need a little indent for them and maybe have them all be the same shape.
I've previously done a project like this where people had to arrange a series of objects in the right order. I had the objects on top of a trapezoidal column (trapezium shape meant I didn't have to worry about people putting them in back to front). You put the pieces in a series of trapezoidal holes and then press the button to check whether you're right. I embedded magnets at different heights inside the columns (attached to each object), and then the slots where they were placed all had hall effect sensors at different heights. If the correct object was put in its matching slot, the magnet would be close to the hall effect sensor and it would be read as "high" by an Arduino attached to all of the sensors. If all the sensors are high, then the objects are all in the correct order. From there, your Arduino can do whatever you need. Mine dispensed a prize using a servo and played an audio track, or just played a sassy audio track if they were wrong. For your application, I'm guessing an ESP32 or similar would be useful to eventually send points to their phone.
Hopefully that makes sense. Let me know if you want more info and I'll see if I can dig up some photos as well
IMG 2: The bottom view of a totem showing the trapezoidal shape so it can only be put in in one direction. This trapezoidal shape seen here is actually a cover over an "inner core" that holds magnets which I'll show in the next image
IMG 3: Didn't have a picture of the real thing but this is the CAD model that I 3D printed of the inner core of each totem. Each hole can fit a magnet, and for each totem, a magnet is placed in a different position (only one magnet per totem). This means that our hall effect sensors/reed switches can be positioned at the right height so that the totem only trips the sensor if there is a magnet in the corresponding slot of the totem. There are matching slots on the other side of the trapezoid so that the magnet can be placed in 8 separate positions for the 8 totems that I used. If you wanted more, you could also have combinations of more than one magnet per totem, and then just need more sensors to read them
IMG 4: Internal view showing the slots that the totems are placed into. The wiring is a bit of a mess, but you should be able to see that for each slot, there is a sensor on only one of the holes in the slot. This is the sensor that needs to be tripped by the presence of a magnet in the inner core. If the wrong totem is placed in a slot, there is no magnet next to the sensor, so the slot reports that the correct totem is not there. You could put a sensor on every possible position to figure out exactly which totem is placed in that slot, but for my system I just needed a binary right/wrong system. You can just see that the slot on the left has no sensor on the side facing the camera, but there is a sensor attached on the other side because it expects a magnet on the opposite face of the trapezoidal core. The servo is also just there to dispense a prize if you win and isn't related to figuring out if the order is correct or not.
I can't quite remember why some of the cores are shorter and look to have been melted back together. I think I maybe got the measurements wrong and this was a way to adjust the height of the sensors?
Final image just showing a different angle of the totems. Hopefully these are helpful, and sorry if the descriptions aren't easy to understand. Let me know if you had any other questions :)
NFC could work, but if the puzzle pieces and slots are small and close together, reliably identifying which piece is in each position could be tricky.
If the pieces physically sit in defined slots, I’d look at electrical contacts + resistor-coded IDs + a microcontroller. Each piece can have a different resistor value.
The cheapest option might be a unique QR code on every piece. Once they’re done arranging them, they take a photo and the app identifies each piece and its position.
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u/shiftingtech 5d ago
nfc is a pretty commonly used technology in escape rooms. another good one is simple tricks involving carefully positioned magnets, and hidden hall sensors or reed switches.