Hi Bob;
About 5 years ago I went through this same issue when I began flying before
the EM2 was available. I solved it using a 'divide by N' chip. It was a very
basic circuit that worked pretty well, but IIRC it would sometimes become
unstable above ~6K or 7K rpm. This wasn't much of an issue for me as I
typically cruise at <5K. But some others with the 'C' drive would likely run
near this point. I didn't pursue it as the EM2 was on its way (I think I
have serial #0002).
If you go in the archives and search for 'tach divider', you should get 16
messages discussing it along with a couple of pics. I think I still have the
extra chips if you want some to experiment with.
Todd