Forum

Full Version: Tach Pulse Voltage
You're currently viewing a stripped down version of our content. View the full version with proper formatting.
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.

Ralph
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.

Ralph
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.

Ralph
Ralph,
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.