Wiring up to the AN2131

Posted on Feb 5, 2014

It`s just a AN2131 chip with the required support circuitry - crystal oscillator, power regulators etc. First I took the inputs and outputs of the key matrix and wired them to the GPIO ports of the AN2131. This was just a matter of plugging the whole lot into some protoboard. This didn`t work too well, as the keys would get `stuck` often. This is because an unconnected chip leg can `float` between

Wiring up to the AN2131
Click here to download the full size of the above Circuit.

on and off due to the residual charge held in the wire. The solution is to add pull-down resistors which allow this residual charge to flow to ground when the key is released. I added one to each input of the circuit. I used a variety of spare resistors from the junk box 320 ohms to 1000 ohms. This is the final circuit diagram:

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