Embedded: Tach Success!

It worked! The filtering hardware that I built (zener diode + MOSFET) gave a clear enough signal to simply trigger off the falling edge of the input spikes; this was the trigger condition for my hardware interrupt.

I recorded the time intervals between pulses for four individual events in a buffer and then used the average to calculate RPM. The results speak for themselves:

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Embedded: EDIS Tachometer Signal

I’ve been scratching my head as to why I can’t get a decent tach signal for my pneumatic gearshift system. The 12v square wave signal comes into the micro controller via a zener diode and a switching MOSFET. The pin is held high through a pull-up resistor and grounded by the MOSFET. The zener diode cuts the bottom 5 volts off the tach signal to remove any noise around the 0v value.

My mistake, and I think its a fair one, was believing the square wave tach signal would have an equal time high as it does low; at a constant engine speed.… Read More