[Diy_efi] Info on how to make crank position sensor circuit?

[Bruce]

I wouldn't suggest knocking two teeth off a SBC's flywheel.
The starter's gear is only like 10-12 teeth, missing two on the flywheel
will reduce it to junk really quick (the ring gear).
Bruce


----- Original Message -----
From: "Perry Harrington" <pedward at apsoft.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, June 05, 2002 1:47 PM
Subject: Re: [Diy_efi] Info on how to make crank position sensor circuit?


> I believe that the car makers already made it trivially easy for us.
>
> I was thinking about this and realized something.  The 60-2 wheel
> is to the developer's advantage.  You know that it's physically
> impossible for an engine to double or halve it's rpm in 6 degrees
> rotation, therefore the missing 2 teeth solves the problem.  If
> the pulsewidth between falling edges of the teeth more than doubles
> from the last sample, you know you hit the -2 teeth.
>
> The pulsewidth between falling edge should triple in the -2 teeth
> gap.  That's a very large sentinel value and does not require any
> special PLLs or trick algorithms.
>
> If you're looking for a good circuit that will detect an ignition
> signal, refer to the DIS ignition article on the diy-efi.org website.
> The article uses an LF357 opamp as a comparator to detect the zero
> crossing point of the VRS sensor.  I used an LM324.
>
> There are 2 issues with the design that you should be aware of however:
>
> The 10M hysteresis resistor is prone to making the opamp oscillate when
> any noise may capacitively on the inputs.  I built this
> circuit last night and played around with it.  With the input open it
> made no noise until I held the input wire in hand, then a ~60hz signal
> was imposed on it.  I replaced the 10M resistor with a 1M and the noise
> went away.  Using guard traces will improve this as well.
>
> You can observe the sensitivity of the circuit easily.  With the 10M every
> crossing of the VRS sensor would cause the opamp to flip-flop.  This
> is handy for detecting very slow crossings, however it also makes it prone
> to noise.
>
> The other issue is the 10k trim pot to set the comparator voltage.  This
> is useful in a DIY system for tailoring to your setup.  I would recommend
> a 100k or 500k pot for this, as by the time you adjust the trimpot down
> to the value you want, the current would be too high.  I found that a
> good value for the voltage divider was 100k on the high side and 2.2k on
> the low side.  The 2.2k keeps the current at sane levels (instead of
220ohms)
> and the 100k doesn't impose any real issues.
>
> Also, you can substitute out the 1M input resistor, I'd choose 10k.
>
> You might also try adding a 100k input pullup.
>
> --Perry
>
> On Wed, Jun 05, 2002 at 01:02:24AM -0500, bcroe at juno.com wrote:
> > If I wanted to resolve between teeth, I would keep track of the
> > time between the last 2 teeth passing.  I would divide the time
> > since the last tooth by the time between 2 teeth to find out how
> > far past the last tooth I am.
> >
> > Phase locked loops are a tricky business, esp for widely
> > varing frequencies.  Bruce Roe
> >
> > On Tue, 04 Jun 2002 14:49:53 -0700 David Gravereaux
> > <davygrvy at pobox.com> writes:
> > > bcroe at juno.com wrote:
> > >
> > > >Just how much more accuracy than individual flywheel teeth
> > > >is really useful?  Bruce Roe
> > >
> > > Whether I infer in hardware (integration in the loop filter
> > > of the PLL), or infer by time in between teeth, it's the
> > > same result (hopefully).  As I have no idea how to do a
> > > DPPL, I'll start with a 4046 and a timer used a
> > > programmable counter and see where it gets me.  A
> > > quarter of a degree
> > > resolution seems like a good starting point.
> > >
> > > If I can get it to pass the strobe test with a gear on a
> > > drill jacking the rpm all around, i'll be pleased.  From
> > > the archives, someone advised a DPPL to be more
> > > adjustable with regards to noise rejection because
> > > all the math is right in front of you.
> >
> > > David Gravereaux
> >
> > _______________________________________________
> > Diy_efi mailing list
> > Diy_efi at diy-efi.org
> > http://www.diy-efi.org/mailman/listinfo/diy_efi
>
> --
> Perry Harrington             Linux rules all OSes.               APSoft
()
> perry at apsoft dot com                  Think Blue. /\
>
> Those who would give up essential liberty to purchase a little temporary
safety
> deserve neither liberty or safety. Nor, are they likely to end up with
either.
>                              -- Benjamin Franklin
>
>
> _______________________________________________
> Diy_efi mailing list
> Diy_efi at diy-efi.org
> http://www.diy-efi.org/mailman/listinfo/diy_efi


_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi