Paul,


I read your write up on the analog tach circuit and would like to

Incorporate it into my engine monitor.  I am trying to understand how it works.

http://www.rotaryeng.net/Open%20source%20ARM%20based%20EFI.html


The pulses coming off of the CAS are causing an increase in output voltage based

 on the number of pulses occurring per unit of time.  I would like to use perhaps the flywheel teeth

with a ABS sensor as an input.  I am using an RX 8 wheel so I don’t know if that would work with your circuit.

What components determine the range?  You are going from 0rpm 0 volts to 8000rpm?

Or 3.3volts?  What components are selected for the sensor input pulse?



Joe Berki

Lets say you set the LM1815 reluctance sensor chip up for the teeth on the flywheel.


What you need to do is adjust R on pin 14 to give you a pules width
that you can still see at 8000 RPM.

Assume you have 100 teeth on the flywheel.

Assume for the moment it still works at 800,000 pulses per minute or 13,333 Hertz.
Then you need to choose a cap on pin 10 . Lets say it is 1 uF. Now you need to choose
or adjust the resister on pin 10 to just give you 4.5 volts at 8000 RPM and less
voltage at all lower RPM's.

The chip was designed to work with a CAS and that flywheel maybe too many
pulses per second. 5,000 Hertz is mentioned in the attached LM1815 pdf on page 9.

Let me know how it goes.

Paul Lamar

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