RPM with wire and PIC

Hello Steve,

You mentioned a while back of a couple of coiled 18gauge wire wrapped on a spark wire, and using that to measure RPM.

I am working on building a CHT, RPM, Hobbs for my Ultralight. If possible, to build some kind of Digital Air Speed indicator.

What did you use to isolate the wrapped wire from the spark plug?? Just a 5 volt Zener Diode?

And on a CHT they use a coupler? on the spark plug... Is this coupler a Thermoresistor? and if so, do you know the range of this Thermoresistor?

I figured with the RPM, I could use that to activate my clock, so that the clock will run only when the RPM's are a certain value. (like >500 RPM). thus the Hobbs meter would be RPM activated.

Dwayne

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What did you use to isolate the wrapped wire from the spark plug?? Just a 5 volt Zener Diode?

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you just need one wire end...like an antenna. With this, since the signal will be really low, i was using an operational amplifier to increase the amplitude.. gain >100. Then i'd place this output to an voltage comparator to create a cleaner *square wave* output directly to the PIC. use of an double op-amp like tl072, ne5532 or other works.

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I am working on building a CHT, RPM, Hobbs for my Ultralight. If possible, to build some kind of Digital Air Speed indicator.

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not really familiar with those application but, maybe some automotive or else air flow sensors can do the job as well as you want.

BTW i found this doc about using thermistor to measure air velocity.

http://sensors-transducers.globalspe...itepaper%2Epdf

there's certainely other method but, this is the only one who comes to my little mind for now.

Hey Dwayne, did you clean your PM... last time i try to post you something, it was full.

regards

Hello Steve,

Steve>>Hey Dwayne, did you clean your PM... last time i try to post you something, it was full.<<

Yes <g>, Did it yesterday... I can't believe they limited me on PM's....

Dwayne