Re: DIY Pachinko ball counter
Try a schmitt-trigger buffer between the opto-transistor and the input to the XOR. The output of the opto transistor is an analogue signal where the voltage is proportional to the amount of light hitting the sensor. The input to the logic gate is digital, below a certain voltage is a '0' and above a higher voltage is a '1', this means that there is an indeterminate zone between the two voltages, and a signal in this voltage range may produce a '0' or a '1' input or may even induce oscillation. Putting a capacitor across this input will help reduce oscillation, but cannot remove the fact that you have an analogue signal that is passing through this indeterminate voltage range.
A schmitt-trigger gate has hysteresis applied to it's input, it won't change to a '1' state until the input voltage is above a relatively high level, and once it's changed it won't change back to '0' until the input is below a lower voltage level. This way there's no indeterminate zone, and you should see nice clean input transitions.
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