Bug zapper project with counter
Sensing the voltage on the output cap should not be too difficult.

My guess is that there already is a bleeding resistor in parallel with the output capacitor. For a crude circuit, you can add a few diodes on the bottom side, so that you see a high to low transition when a bug is zapped.







simulate this circuit &ndash; Schematic created using CircuitLab

This works only if the cap is fully discharged when a bug is zapped, which is unlikely. Worth a try if you have some diodes around, and a fair amount of bugs too.

You can give another shot to capacitive coupling:







simulate this circuit

Note that C2 here should be able to withstand all the output voltage.

In DC the voltage to the micro is the Vdd, through R2. When a bug is zapped, the voltage of C1 drops (a lot), so does the voltage to the micro. D2 protects the micro from negative spikes, you might be fine with the protections inside the micro itself.

D1 is probably not necessary, as the voltage rises quite slowly on C1 so basically you charge C2 and do not see positive spikes. I would simulate that, just in case. If you really need to dump a lot of charge on Vdd, you might need a resistive path to ground, some 10 mA or so. Also lowering C2 should help.