Don't always work out.


David Josephson,

My 555 based voltage to frequency converted worked sort of but only
in the range of 9 volts to 12 volts.

Do you have any experience with the KA331 ? I ordered some from
Mouser.

Paul Lamar

I don't, but it certainly looks like a better approach than a 555. It
seems to be Fairchild's take on the National/TI LM131/231/331 which
is now made by TI. There is a lot more information on the TI
datasheet than Fairchild's.

David Josephson


Thanks David.

The Ti parts are 5 times more expensive. I don't need anything too
fancy or too accurate.

Here is what I am going to try.

Paul Lamar


Paul,

I have been working with the LM2907 and the Lm2917.  I had a problem
with the signal off of the CAS as the signal did not agree with the
calculated frequency.

I put the LM1815 in between the CAS and the Freq to voltage converter
and the problem went away.

I had to capacitive couple the signal from the LM1815 and used a 10k
to ground to offset the signal so it would cross  zero.

Use the 8 pin chips as the 14 pin is more difficult to work with and
part count is lower.

I also had a problem getting the rpm vs output voltage curve to be
linear with the 24 tooth wheel.

I use the 2 tooth wheel adjusted the capacitor and got a linear
response form 400 to 4500 rpm using a variable speed drill press and
a optical hand held tach.

The data sheet for the LM2907and LM2917 is a bit confusing.

Joe Berki


Send me a schematic  with the colors of the wires you connected to
coming out of the CAS.

Paul Lamar



Paul,

I used the cable from the car harness between the CAS and the circuit.
I know I was on the 24 tooth vs the 2 tooth because of the frequency
measured.  24 tooth 4500 rpm 1800Hz.  2 tooth 4500 rpm 150Hz.

Joe Berki




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