Tach Pulse Voltage - Printable Version

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Tach Pulse Voltage - Ralphxyz - 05-02-2017

re: TouchDRO "iGaging" board

Most of the tachs I have seen output a 5v or greater pulse.

Would I need to reduce the pulse voltage to 3 volts for the TouchDRO "iGaging" board?

I am sure this has been asked but I do not remember seeing a answer.


RE: Tach Pulse Voltage - Ralphxyz - 05-04-2017

Darn 17 views and no one knows the answer.

What would happen if I put a 260µ resistor in line that would drop 5 volts to 3.32 volts would that work?

Seems strange to have to do this but it really seems strange no one knows the answer.


RE: Tach Pulse Voltage - Ralphxyz - 05-07-2017

Well using a resistor works.

Sort of.

This is with a Hall Effect sensor.

The RPM reads 720 and then 600 and then 720 and then ... while the speed is staying constant.

I am also getting fluctuations with a optical sensor so I need to fiddle with it.

Plus the reported rpm is it seems to low.

I am having trouble getting my test laser rpm sensor to get a reading.

Duh, I just figured out what to do to get my laser sensor working Duh.


RE: Tach Pulse Voltage - Eskimo2k - 05-09-2017

Check the signal voltage coming from the tach. If it is greater than 3.3 VDC you MUST use a voltage shifter or a voltage divider or you will let the magic smoke out of the MSP. I would suggest using the LM339 voltage shifter circuit that Yuriy laid out in the build instructions.

As for the tach.... that may be a little more complicated. You may want Yuriy to comment on that.