RPM with wire and PIC

[Dwayne]

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

[mister_e]

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

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.

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

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

[Dwayne]

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