Pang,

Hopefully this won't come across as critical or condescending, but it seems
that you do not have very good know-how or experience doing these things.  I
highly recommend that your entry into electronics (or this part of
electronics) not be on a vehicle, where not only are there mechanical
dangers, but also high-voltage dangers (like at the ignition coil).  Perhaps
for now you can find a commercial unit to do whatever it is you are trying
to do?  If I'm wrong here w.r.t. your knowledge, then I apologize.  Either
way, be careful.

Cheers,
-Neil.



> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Pang
> Sent: Sunday, November 24, 2002 8:32 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]:Where to tap tachometer signal?
>
>
> Hi all,
>
> Thanks everyone for your feedback. Guess I need to take a book
> and check out
> the terms of Alternator, Distributor, etc.
> It doesn't help when I am still riding my 10 year Honda scooter after all
> these years.
>
> Anyway, the conclusion is that I need to tap either from -
>
> 1.  The negative side of a coil primary
> Pls check if my understanding is correct. There is only one
> ignition coil in
> every typical car, but there are definately more than one spark plug ( for
> each piston ). The ignition coil will generate a huge current to fire a
> spark plug and there will be a device that behave very much like multiple
> relays that distribute the the current to the respective spark plug. And
> that relay like device is the Distributor, correct? Which is why Chris
> mention about dividing the reading obtained by the number of spark plug to
> get the real Revolution per minute.
>
> 2.  tap the ECU signal going to any one of these coil-packs for new cars
> without distributor
>
>
> One question is how the tapping is done? I've seen a colleague of
> mine using
> a simple wire and make several rounds at the cable leading to the
> spark plug
> (without tapping directly to the wire). The tapped signal
> obviously has low
> amplitude, but it seems to be workable. Or perhaps I should search for the
> wire that goes to the rpm display module ( that will be easier to
> connect )
> One problem which I foresee now is when the unit is installed at different
> cars, and the tachometer reading is tapped from different source.
>
> Have a nice day.
>
> Rgds,
> pang
>
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