This works like a charm. Pulse amplitude is constant.
Not a function of gauss. Pulse width varies according
to RPM which of course makes sense as the magnet is
in front of the sensor for a longer period of time
at low RPMs.

Distance is not as sensitive as I thought. The
gap can be as much as a 1/4 of an inch and it still works.

I will have to condition the trigger to get a narrow
pulse off the down going part of the wave. In other words
the leading edge of the negative pulse.

The scope was set to 10 ms per division and this
was roughly 3,000 RPM. The pulse width was about
5 ms wide at this RPM. The vertical axis was
one volt per divisions so the output was about
5 volts peak to peak. Just about rail to rail
as the power supply was set to five volts.

This device greatly exceeded my expectations by far.
In other words it beats the heck out of an ABS sensor or Mazda
crank angle sensor.

It is also one tenth as costly.

Next step is get another couple of magnets from Radio Shack so
I can double the effective RPM. Either that or get a faster drill
motor. Maybe I'll add four more to check the RPM to 9000.

BTW speaking of speed Klaus has no trouble hand propping his
O-200 with Hall effect ignition sensors.

Paul Lamar
--

Paul

Use your electric disc grinder and a chopper circuit to control rpms.  It
will go over 12,000 rpms.   Air rotors tools 100K rpms with a bleeder
valve are another option.

Doug in Japan.

Your right. It is a better test to use a high speed motor
rather than add more magnets. Not the same thing. One needs to
get those magnets going fast enough so they spend
the proper amount of time in front of the sensor.

Come to think of it I have a Dremel tool at the hangar.
I think that maybe fast enough. I looked them up
on the net and they have a variable speed unit 5000
to 35000. That would be real handy. I'll have to make a
new magnet holder disk. The Dremel I have could be
35,000 RPM fixed. That could be dangerous with a larger
diameter disk.

I just remembered I have an old  DC unit at the hangar with
a lost charger. I was going to throw it out. I'll take the
battery out and hook up a variable DC supply. Should go
10,000 RPM or so.

Paul Lamar