Howdy,
What I have here is an automotive tachometer circuit, specifically the (-) PWM input to the microcontroller.
From looking at the pinout on the microcontroller used, this circuit seems to convert the (-) PWM from the ignition coil into an analog input signal.
I'm just getting into this stuff, have made a few of my own PCB's with success, but this circuit has me puzzled.
How exactly is it converting the negative/ground PWM to an analog 0-5v signal?
also, my BIGGEST point of confusion is what appears to be a Zener diode on incoming PWM at the very beginning after the current limiting resistor.
what is this Zener doing? I assume its of a 5V persuasion since the linear regulator (78L05) on the same circuit is of a 5v output - but I'm just not sure.
any help in explaining exactly what is going on here would be greatly appreciated!
just getting into this stuff, and really enjoying myself.
(ultimately trying to accomplish the same, receive an analog signal to my own microcontroller. the arduino stuff just isnt fast enough to track an interrupt accurately past a certain RPM point, not to mention handling an interrupt to generate an RPM readout doesn't allow you to do much else, where an analog input signal is much more easy to work with.)
What I have here is an automotive tachometer circuit, specifically the (-) PWM input to the microcontroller.
From looking at the pinout on the microcontroller used, this circuit seems to convert the (-) PWM from the ignition coil into an analog input signal.
I'm just getting into this stuff, have made a few of my own PCB's with success, but this circuit has me puzzled.
How exactly is it converting the negative/ground PWM to an analog 0-5v signal?
also, my BIGGEST point of confusion is what appears to be a Zener diode on incoming PWM at the very beginning after the current limiting resistor.
what is this Zener doing? I assume its of a 5V persuasion since the linear regulator (78L05) on the same circuit is of a 5v output - but I'm just not sure.
any help in explaining exactly what is going on here would be greatly appreciated!
just getting into this stuff, and really enjoying myself.
(ultimately trying to accomplish the same, receive an analog signal to my own microcontroller. the arduino stuff just isnt fast enough to track an interrupt accurately past a certain RPM point, not to mention handling an interrupt to generate an RPM readout doesn't allow you to do much else, where an analog input signal is much more easy to work with.)
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