On AC-CDI v7.9, DC-CDI v7.9 or DC-CDI v2.1 the tacho output available at RB5/PIN11/TP1 can drive a tachometer.
The signal is a +5volts level and 5% Duty Cycle signal:
but some tachometers need a +12v level at 50% DutyCycle signal !
In order to work with such tachometers I created a small microprocessor able to convert the Duty Cycle while keeping the same frequency.
|Output Duty Cycle||50||%|
|Input Duty Cycle||0.1||99.9||%|
The processor convert the input signal to an even 50% ratio.
A +5v level 50% DutyCycle is available at pin2, then a NPN transistor raise the signal to a +12v level.
Extend 0.1% DutyCycle at 8Hz:
or shrink a 99.9% DutyCycle signal: