Trying to decide on RPM & crank angle sensor

[Tony Bryant]

>We had originally thrown around the idea of using an optispark style
optical
>sensor, but I think there must be something easier than that. Has anybody
>ever tried using an optical encoder? I don't know much about them at all,
>but from looking at the spec sheets it seems like they would work, and I
>wouldn't have to try to cut out a disk and make it work with a sensor.
>Anybody know of a good source or where I could find some datasheets?
>

I used a piece of PCB material with 59 holes drilled in it bolted to the
crank pulley.
I used a optical slot sensor from a old mouse. Worked great, but it made me
nervous
so I changed to a hall effect sensor.

>Hall effect sensors seem to be very popular. All you need is a toothed
wheel
>and a sensor, right? What does the output signal look like?

Order a hall effect gear tooth sensor from digi-key. Make sure you get a
gear tooth sensor, not just a normal sensor. Allegro make a nice one that
outputs TTL with no bounce or other crap. I just expoxied it, a tiny rare
earth
magnet, and a piece of steel (to act as a pole piece) in a piece of copper
tube.
Pretty robust solution.

Just to be sure though I feed the result through an RC filter and an 74HC14
to
square it up again.

I did mill up a fancy 59 tooth wheel for it, but I could have easily just
cut a few slots in
the periphery of the crank pully.

Digikey also sell complete hall effect sensor from Cherry, ready to bolt up.

>
>What do you guys think would be the most reliable and accurate sensor? Ease
>of implementation is also a factor, not the biggest, but it is a factor.

Don't bother with inductive at this stage, the lack of DC response will make
the engine a bitch to start, if you don't get the signal processing right.




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