The reed switch matrix

   
64 reed switches are needed to build a 8x8 matrix. There's a big difference with a microswitch matrix as used in Sish Chessboard project: Any square containing a piece will have its reed switch activated. In a matrix like this can occur "ghost" activations, ie, when the microcontroller scans the matrix it "can think" that there are some switches activated when in fact they are not. This effect, known as "ghost key", is solved by adding a diode in series with each of the switches. You can learn more about this effect in the following document: Ghost_Key.pdf



Diode

 
  Any signal diode may be suitable. A good option is the 1N4148


Ghost effect


  Attempts to explain how a keyboard matrix works, what "ghosting" and "masking" are, and how to prevent them. by Dave Dribin

  link






Notice: Alternative to the PCB


    If the difficulty in building the PCB (Printed Circuit Board) prevents you perform this project, don't worry, they are not essential. You can choose to build the matrix of reed switches on the bottom of the chessboard, gluing them with thermic glue, then using cable to make the wiring.

    However, regardless of the building method chosen, you should experiment (before the construction) with the distance between magnet and sensor (reed switch), in order to avoid subsequent problems.

Example of a chessboard in which "grooves" have been conducted in the
diagonals of the squares (on the bottom side). Then all the reed switches
have been glued with its diodes soldered. Finally the matrix has been wired.