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I want to build a Scrabble board that detects tiles placed, mainly as a one off challenge and learning experience (i.e. not a commerical product). I haven't started building yet: I'm trying to work out the most practical general approach so I can focus my learning/experimenting in that area.

So board = 225 squares, and I want to "sense" any one of 27 unique letter tiles (including blank) unsing an arduino.

There are a number of approaches I have been pondering:

  1. Commercial RFID - 225 squares each with their own commercial RFID reader seems impractical and expensive...
  2. Induction and Resistance - I believe RFID (and NFC) work off induction, so I could theoretically build 225 of my own simplistic version of RFID/NFC using a simple circuit coupled with 27 unique resistor values and read different induction feedback values?
  3. Encoding 5 Inductors - If noise and sensitivity are an issue trying to reliably detect 27 different values, assuming i can at least detect "on or off", I could create 5 readers for each square, and my tiles could have 32 unique patterns of copper pads/coils to trigger those 5 readers (i.e. construct a 5 bit unique identifier)
  4. 1 inducer pad, 5 induced pads - Thinking about how the circuit might work in option 3, I'm thinking a circuit where I have one pad in the board acting as the 'inducer' with oscilating voltage supplied, the tile can be one single 'induced' copper pad with 5 possible combinations of 'copper pad areas' that would be read (or not) by five 'feedback induced reader' pads in the board. With this and 3 im not sure if i can get away with ~5mm copper pads, or i would have to make ~5mm flat coils? Because 225 x 5 coils would be difficult...
  5. Capacitive Sensing and Simple Encoding - maybe a stronger signal than induction and maybe easier than building coils? Perhaps they're very similar? But maybe the capacitors would be so small (i.e. diy copper plates ~5mm square) the arduino will struggle to see a noticeable difference.

I'm currently focused on option 5:

  • Most videos/articles are around using human fingers on a single plate: it seems this is "easy" because the body acts as an affective ground in that circuit (body = second plate of capacitor)
  • Maybe copper plates in the tiles (above copper plates in the board) would work? But they wouldn't be grounded, so maybe little effect?
  • Intead, maybe build both plates of the capacitor on the board: so each square has 5 true capacitors: two ~5mm plates on top of each other with thin insultating material in between... perhaps that will react more strongly when a copper pad in the tile is placed above it?

Maybe all of those approaches would have too much noise? Maybe they all still have hard problems to solve? But if someone says "approach X would be Y times easier" then that will be encouraging guidance for me to jump in to the hard work :) Thanks, sorry it's not a more specific/precise question!

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    \$\begingroup\$ I doubt 1. would even work. You can't place RFID readers so closely to each other and still reliably detect which one is closest to the stone. \$\endgroup\$ Commented Jul 12, 2024 at 8:45
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    \$\begingroup\$ Note that at the end of the game, you will have ~200 pieces simultaneously on the board. Interference will be a big problem. \$\endgroup\$ Commented Jul 12, 2024 at 8:50
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    \$\begingroup\$ Search this site for "chess". Many similar questions have been asked before. There are also commercial solutions, such as from DGT: digitalgametechnology.com/products/home-use-e-boards \$\endgroup\$ Commented Jul 15, 2024 at 17:20
  • \$\begingroup\$ Thanks Pascal appreciate the guidance \$\endgroup\$ Commented Jul 17, 2024 at 2:15

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