I'm trying to understand this circuit (see attachment), so I can build it. I have ordered a Speeduino kit and so I can study the Engine Control Unit (ECU) signals. I believe this circuit is supposed to be able to provide an RPM (tach) signal that can be recognized by an ECU. I have not been able to determine the voltage rating of Zener Diode D4. I'd also like to know why the Zener Diode is in parallel with polarized and non-polarized capacitors.
Can someone explain the Zener usage in the circuit?
TIA
Can someone explain the Zener usage in the circuit?
TIA
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