This circuit, right out of the National LM311 comparator
data sheet, works great. Gap was about
.125 inch and starting RPM was 350 ms period or 2.85 Revs
per second or 171 RPM. You can see that in the scope pict.


Upper trace pin 3.
Lower trace pin 7 no scope probe. Direct connection to the scope.

Nothing special on the wiring as the RX8 trigger wheel
and CAS were six feet away from the LM311. Lots of hum
from the florescent lighting in the room and it still
worked great.

Highly recommended.

Chip chip at around 50 cents.

Paul Lamar