Building a stimulator

[Bevan Weiss]

I think that at these kind of frequencies an analog filter just wouldn't cut
it, the passband of the filter would be too great(without talking bout
crystals/ceramics).  And that's even if you can get an adequately stated
passband.  After all if you try and filter out the harmonics for a 1000RPM
signal, then surely you wouldn't be able to pass a 2000RPM signal, let alone
a 5000RPM signal.  And only a couple of harmonics are needed before the
signal doesn't look very sinusoidal anymore...

I would be more inclined to think that the reason that the ECU isn't being
fooled is that it's expecting a negative shoot, the waveform should go
sharply negative then positive (or vice versa).  However a zero crossing
should occur, and I would believe that it's this that the ECU would trigger
on.  You could do several things...

Use the sqaure wave to trigger a seperate transistor which could drive an
inductor to create a ringing whenever a pulse is applied.  This will give a
zero crossing, but may give more than one...

Possibly use some kind of DC offset (with reference to the detector circuit)
so that when the pulse is applied the detector see's a zero crossing.

(NB: This all assumes an inductive 2 wire pickup is normally used to create
the signal.  ie it would go negative as the ferous material comes closer to
the pickup, and then positve as the ferous material goes further away from
the pickup)

PS: I haven't done as much in the EE field as some others on this list, so I
would take other advice (esp: Bruce's) over mine.

----- Original Message -----
From: <goonie.gordon at talk21.com>
To: <diy_efi at diy-efi.org>
Sent: Tuesday, April 09, 2002 2:36 PM
Subject: Re: Building a stimulator


> Hi Wayne,
>           I'm surprised that the square wave does not register as a
trigger.  If you want to convert into a sine wave then it's easy as a square
wave is made up of harmonics of the basic sine wave - All you need to to is
make up an active unity gain low pass filter with some capacitors, a couple
of resistors and an op-amp.  Anyway the filter should pass only the
fundametal frequency and hey presto one sine wave.
> This stuff should be easliy picked up from academic text books on
electronics but if your having trouble I could look out some examples.
> :o)
>
> >  from:    Wayne Macdonald <wmcdonal at optushome.com.au>
> >  date:    Tue, 09 Apr 2002 13:24:48
> >  to:      diy_efi at diy-efi.org
> >  subject: Re: Building a stimulator
> >
> > I am building a stimulator to run a Sagem ECU on a test bench, I want to
> > generate the crank trigger from a micro but I am having problems.
> > The ECU expects to see a waveform from a normal two wire crank trigger,
The
> > square wave I am generating does not seem to fool the ECU.
> > Can someone help me with the circuit required to convert a square wave
into
> > a sine wave.
> >
> > Thanks
> >
> > Wayne
> >
>
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