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Hey guys as described here I also want to make a chess board with some arduino support. Here I want to ask some questions regarding the schematic and the pcb layout I am planing to do. @Dmitry Grigoryev describes a way to address the sensors by using a 1-8-demux. Due to the fact that my schematic skills are still not the best please bear with me. Anyway, I want to describe my idea briefly.

  1. Schematic for field

    For version 1 of our board we planing to integrate photo-resistor to determine whether a figure is on a field or not. For this I want to share a simple schematic: enter image description here

This maybe looks stupid for some of you but these are my first tries. My idea behind this is to use the photoresistor and the other resistor(where the resistance varies from field to field) as a voltage divider to determine which exact field is triggered by a figure.

Question 1: Is this feasible or does anybody has a better idea, then please share with me?

  1. Communication with controller

    We are aiming to use a Arduino Micro/Nano or Mega if more memory is needed. For the communication we choosed the MCP23017 - I/O-Expander. So every field is connected to one out of 4 controller(64 fields = 4 * 16bit I/O expander). I know its an analog signal but all I need is just a 'hey i got triggered' signal.

Question 2: Is this also feasible or does anybody of you has a better and more clean solution. More maintainable and more expandable for future versions.

  1. PCB

    I am planing to create a PCB out of all ideas that are expandable for other usecase(e.g. adding ADC etc. or something like this).

Same question as former ones also.

Puhh I hope I added everything and the question full-fills all stackexchange standards. If not, please provide feedback to enhance my question.

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  • \$\begingroup\$ Wouldn't you rather like to know what type and color the figure is? \$\endgroup\$ – ott-- Apr 4 '16 at 18:54
  • \$\begingroup\$ @ott-- Totally true, thats the step for further versions. For version 1 we concentrate on the very basics facts. \$\endgroup\$ – ckruczek Apr 4 '16 at 18:55
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    \$\begingroup\$ " ... please bare with my". Are you inviting us all to get naked or do you mean "bear with me"? \$\endgroup\$ – Transistor Apr 4 '16 at 19:13
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    \$\begingroup\$ if you add an LED(or change to a optocoupler, ie QR1113) and make the light reflection chamber a closed system and paint the bases different grayscale tones, you might be able to identify parts by how much light they reflect back \$\endgroup\$ – Wesley Lee Apr 4 '16 at 19:25
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    \$\begingroup\$ It wouldn't be too difficult to put two coaxial contacts on the bottom of each piece, that would mate with contacts on the board. Two wires is enough to supply power and communicate data, see Maxim's 1-Wire protocol. \$\endgroup\$ – uint128_t Apr 4 '16 at 19:26
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As per comments, I'm posting an alternative solution that may better suit your needs.

If you make the base of the piece and the square in the chessboard a closed system, you ~might~ be able to identify parts by how much light they reflect back.

For this I believe you need 4 things:

1 Chessboard and piece to be a closed system (outside light may mess with readings depending on what sensor you use)

2 Paint parts bases in different grayscale tones.

3 Add a fixed/known light (might be IR LED, QRE1113 for example, eliminating the LDR)

4 Use a port expander with analog inputs (quick search gives a few alternatives: ADS1015, MCP3424

I've used the QRE1113 under many conditions and it manages to reject ambient light very well. I've only had problems with direct sunlight on it.

I believe you need 6*2 different "grays" (king, queen, rook, bishop, knight, pawn, black and white). I have no idea how hard or easy it is to achieve this precision on print/light sensing. Its very easy to prototype though. You dont even need the i2c port expander.

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    \$\begingroup\$ it just ocurred to me, if one gray gets too similar to the next step, you might want to try green/red bases(for black and white pieces) and coloured gels on your sensors. Some sort of smart combination might give you all the data you need for the part. \$\endgroup\$ – Wesley Lee Apr 4 '16 at 19:57
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    \$\begingroup\$ Not sure why you need to distinguish the pieces. My 80s chess computer had a "button" for all fields under the board and you pushed down a piece you wanted to move and pushed it onto the field you moved it to. Worked fine and ca n these days be replaced by lots of different methods \$\endgroup\$ – PlasmaHH Apr 4 '16 at 21:10
  • \$\begingroup\$ Thx for your answer. This solution sounds promising to me \$\endgroup\$ – ckruczek Apr 5 '16 at 7:16

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