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