Ign Advance on MR-2

[Les Newell]

> I've heard a lot of talk about magnetic reluctor sensors and the
associated
> circuitry.  What about a Infra-Red emitter/receiver pair who's output goes
> through a Schmitt trigger?  This seems easier to design around...  What am
I
> missing?
The circuitry that is needed for magnetic reluctance sensors is actually
quite simple. My circuit uses 2 diodes, two resistors and a comparator.
Reluctance sensors are simple, reliable and dirt resistant.
Infra red sensors have to be shaded from light and protected from dirt.

>
> I could have two wheels attached to the crank pulley, one with 1 tooth,
and
> one with 4 teeth.  I might have to run the output through a flip-flop to
> reduce the frequency 1/2...  Then use a 2-bit counter to select one of 4
> transisters to turn on, which in turn charge/discharge the coil.
>
> This seems simple, actually.  Am I missing something?
>

Why use 4 coils? Most DIS systems use two coils, one coil drives cylinders 1
and 4, the other drives 2 and 3. This is known as a wasted spark system
because each cylinder recieves two sparks per complete firing cycle, one at
the correct firing point and one just before the top of the exhaust stroke.
Ford Zetec engines are fitted with a neat double coil assemby with 4 HT
leads which is ideal for a home-brew DIS. The only production DIS I know of
with 4 coils was a coil-on-plug system by (if I recall correctly)Volvo.

How are you going to work out the advance?

Les

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