(Fwd) thanks for the sensor info

[Orin Eman]

> So in simplified terms, my new ecu will have to see the flywheel
> ignition timing reference pin go by, wait 62 degrees of rotation (or
> whatever is appropriate for the amount of advance desired) by
> counting teeth (2.667x62=~165 teeth), check to see if the
> distributor is sending it's signal to confirm cylinder number one is
> on the compression TDC and not the exhaust TDC, and then fire its
> spark.  After that, it needs to count teeth and fire each successive
> cylinder 27 teeth later (135/5=27).  Does that sound right?

Nope.

Wait for timing pin.  If hall sensor signal is active at this point,
the upcoming cylinder is cylinder one.  If not, continue waiting.
(If you see timing pin without hall signal more than a few times,
throw an error).

Schedule the firing of cyl 1 (62 - advance) * 3 / 8 flywheel teeth
in the future.  You need 2.667 deg per tooth, you had the fraction
upside down.

The next cylinder is 54 teeth later.  TWO crank rotations or 270
flywheel teeth per cycle - 270/5 is 54.

Now when you look at these figures, one tooth is 2.667 degrees.
That resolution is simply insufficient.  So, the ECUs that use the
flywheel teeth use both edges of the flywheel tooth signal.  The MAC11
assumes the signal is square giving resolution of about 1.33 degrees.

> I do have one other question.  What kind of power do the hall
> sensors need, if any?  Are they active or passive (do they require a
> voltage, or do they produce a voltage)?

The hall sensors usually take 5V, ground and have an output which
requires a pullup to 5V.  The MAC11 uses a 5.1k resistor to 5V,
assuming my notes here are correct.

> Also, I'm not even sure if the two flywheel sensors are considered
> hall sensors, are they?  I've been referring to all three relevant
> sensors are hall sensors, but I typically only see the distributor one
> being referred to as such.

The flywheel and timing sensors are 'variable reluctance' sensors.
Basically a magnet surrounded by a coil of wire.  As the flywheel
teeth or timing pin go by the magnet, they change the magnetic field
in the coil and generate a voltage.  There should be a scope trace on
Scott Mockry's site somewhere.

Orin.