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New project: A smart Ouija board

October 31st, 2016 No comments

As it’s Halloween today, one can’t think of better timing for a haunted house-related project. It’s an access control deviceĀ in the form of an Ouija board. The idea is that for the uninitiated it’s just an Ouija with an unusally large planchette, but if you know what it really is, you will use the planchette to point at letters on the board, forming a secret password, and if you get it right, the board will open an electronic lock for you, unlocking a door or a hidden stash. I can imagine this system being used as a prop in a haunted house scenario or a LARP, but this particular one has a commercial application and no details can be released.

 

On the technical side of things, the board is packed with RFID tags, with the hollow planchette sporting an Arduino Pro Mini, an RFID reader, 2,4GHz radio connectivity, a LiPo battery and some other parts. There is also a vibration motor there to provide the user with feedback when a letter is correctly read by the planchette – but the effect is the same no matter which letter is read, so it doesn’t make it any easier to guess the combination.

One curious component I used was a huge 1A reed switch used for automatically switching the planchette into charging mode when it’s put back to its storage location where a magnet is embedded. You can’t see it in the pictures, but the planchette is charged when it is laid on a baseplate with two springs protruding out ouf it, fitting the holes in the wooden cover and making a connection with the nickel plates visible in one of the photos. The plates and springs came from a disassembled AA battery box.

The system comes complete with a receiver switching a relay which can be used to control an electromagnet, an electronic lock or what have you. The receiver is also built around an Arduino and has connection status LEDs and an optional microswitch allowing overriding the system and opening the lock at any time – useful if you forget the password, but you should hide the microswitch properly. The radios used are NRF24L01 modules, so the range should be up to 8-10 metres – I tested it at 5 metres and it worked okay.

 

The wooden parts of this project were provided by the customer who ordered the installation. Arduino code, electrical schematics and detailed instructions for replicating the entire system will be published within the next two weeks.