I took a little hiatus on the robotic chessboard project I have been working on to better plan out some of my methods. I decided that the sensing of the position of the chess pieces will be done by Hall sensors. I will place a Hall sensor under each square of the board. The kind I bought are essentially switches which turn when one polarity is brought towards the sensor and turns off at the presence of the other magnetic pole. I put small magnets in the bottom of each chess piece. In the first video, you can see that the chess piece activates the hall sensor, which lights the LED. I then use the opposite pole of the magnet, which I glued to a stick, to reset the sensor. (Sorry for the vertical nature of the video. One of these days, I'll remember to consistently hold the phone sideways when recording.)
For the operation of the robotic chessboard, these latching Hall sensors pose a problem. As shown in the above video, the sensors would not turn off when the pieces are removed. Hall sensors that do not latch are nearly twice as expensive at the latching kind. This adds up when 64 are needed. I solve this problem by using a digital pin on the Arduino to control the power input to the Hall sensor instead of the 5V pin. This idea comes from the comments on Sparkfun. As you can see in the second video, the sensor now detects the presence of a magnet.
The next step is learning how to control 64 inputs on the arduino with a mux chip, which allows for control of 16 hall sensors using only 4 pins on the arduino. The next update will hopefully show a full chess board which detects where the pieces are or at least progress in that direction.
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