Tach Pulse?

[Ralphxyz]

What is the Tach looking for in a pulse?

I made a tach using a TCRT5000 but that uses a variable analog output (36 - 1024).

Now I am trying some Hall Effect sensors.

One stays High (On) unless there is a South Pole.

Another latches South Pole ON North Pole OFF.

I "had" a IR sensor that I tested at my desk which I assume used a TCRT5000 or something similar.
That seemed to work but I could not verify, compare with another tach.

Now I cannot find that sensor. 

Thanks for the replies.

Ralph

[Briney Eye]

On the Mixed Scale board it's looking for 0-3.3V. 3.3V is available on the header. I don't recall now if the input is 5V tolerant, but if your sensor requires 5V you will have to pick it up somewhere else.

The output polarity doesn't matter as long as it provides a "logic" level that's toggling between the rails.

If you're going to attach a magnet to a spindle then you want the first type. You will have to test it to figure out which pole the sensor is more sensitive to, and then mark that end of the magnet to face out. Or you can use the second type with pairs of magnets mounted with opposite polarity, then you don't have to figure out which pole is South.

[Ralphxyz]

Thanks Briney Eye for the reply.

I have had a led inline with the output so I can tell South Pole easily.

Ralph