> What signal is than connected to the basis of Q3?
It's an antenna input. The circuit is used to detect manipulation using things like a piezo crystal from a lighter to confuse the circuit.
We actually did this many years ago with a Phoenix cabinet.
> Regarding the paddles: Given the input nature of the circuit I would keep the > existing black box solution. Anything else IMHO is a overkill. The circuit is not > exact by design. If it would have been, there would be no variable resistor for > calibration.
Yes, that's what I had in mind anyway. The model of the 555 is only capable of simulating the monostable mode anyway. If any circuit with a 555 as clock generator comes along, I'd have to take some measure to distinguish them.
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