[Diy_efi] RE:photocoupler?

[Mark Bowers & Family]

OK, Steve, Tony,

Now I am getting the picture....a bit slowly.....

Tony, the unbipolar device sounds fine. No reason a normal (unipolar)
photocoupler can't work, if you just observe the polarity. Just make sure
the reverse spike across the coil is suppressed by a diode.

I am a bit curious as to what minimum time resolution you are trying to
achieve. Some photodiodes can be pretty slow, particulary in turning off;
there are other types and techniques to make them very fast.. But you may be
A-OK in this application, depending on how finely you want to resolve the
puslewidth.

One thing to think about twith the bipolar device is any effects from the
reverse spike from the coil when the current drive is turned off. Even with
a suppression diode, you might get a  bit of extended photoemission from the
second LED in the package, as it is partially stimulated by the reverse
spike. So this might speak in favor of a unidirectional LED. I would
certainly have a very good suppression diode in the system somewhere. If
not, I would expect it could take out the photdiodes in short order. (As
well as the solid state devices driving it!)

Mark B.



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