My goal is to build a chess board that can detect the movement of pieces on it. My current approach that I'm testing is to have a reed switch underneath each square and magnets attached to the bottom of each chess piece. I was inspired by this article.

However, in testing, what I'm finding is that when the magnet is dead center on the read switch, the switch is open, not closed! I found this article which was a very helpful overview of why this happens, and what happens in different configurations.

I've considered:

  1. Pole facing down - this has the switch off when the magnet is centered on the switch
  2. Thin bar magnet roughly equal to the diameter of the piece - this works pretty well given that the piece overlaps the center which gives a good enough margin for error; the problem is that it attracts/repels the other pieces next to it too strongly!
  3. Other approaches: RFID (looks more expensive, more complicated to set up, and hard to scan quickly enough), light sensors (requires drilling holes in the centers of the squares which I'd prefer to avoid)

However, I'm still at a loss - is there any clever way I'm missing to set this up so that a piece placed on a square triggers the reed switch, with a solid margin for error (I play a lot of blitz chess)?

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    \$\begingroup\$ When you say "the switch is open, not closed" do you mean the normally-open switch stays open, or that you accidentally bought normally-closed switches and they go open when the piece is in place? \$\endgroup\$
    – Hearth
    Aug 12, 2022 at 5:49
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    \$\begingroup\$ What about putting the switches in a different direction, like vertical? Vertical magnet, and vertical switch? the switch may need to be quite close to the board. \$\endgroup\$
    – user253751
    Aug 12, 2022 at 5:54
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    \$\begingroup\$ I would suggest to try the Hall Effect sensor. \$\endgroup\$
    – tlfong01
    Aug 12, 2022 at 6:34
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    \$\begingroup\$ Hall effect sensors are more reliable than reed switches and can be much more sensitive. Try a few of those. The only downside to them compared to a reed switch is that a reed switch doesn't require power. \$\endgroup\$
    – Drew
    Aug 12, 2022 at 7:05
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    \$\begingroup\$ Okay, thanks everyone for the advice! I ordered a test set of hall effect switches and I'll try them out this weekend. Seems the advantage is that they may be more sensitive + I can orient the hall effect switch any direction I want because it's smaller (3mm on its longest axis instead of 14) and less fragile. \$\endgroup\$
    – James
    Aug 12, 2022 at 15:49


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