This circuit produce modulated 12V impulse packets that emulate RPM sensor output in a device where one of PWM driven 12V DC motor poles and one of RPM sensor switch poles are internally connected to device case in a way that it is not possible to decouple both poles from device case. Simulation use two 555 timers for "garbage" impulse generation and produce periodical impulse groups by cycling impulse amplifier power with P-channel MOSFET as high side switch.
