MAP sensor

[Darrell Norquay]

At 08:19 AM 9/13/96 -0500, Tom wrote:

>Now, I'll just need to find out how much it costs,
>what it looks like, how it mounts, etc.

Typically, most OEM MAP sensors are little black boxes around 2x3x1", with
screw mounting holes built in, a small barbed hose fitting, and a plug or
short wiring harness with plug.

>The data sheets for these are on the Motorola web page,
>(http://motserv.indirect.com/) and they're listed in the Newark catalog
>for about $26. 

The MPX4100 series have all the necessary signal conditioning built in.
They are simple 3 wire devices, voltage in (5V) , voltage out (.2v-4.9v),
ground.  Slap it in a waterproof enclosure and you're done.  They may not
like high vibration environments, so best to mount them on the firewall, in
the passenger compartment and run a hose to the manifold vacuum tree.  These
may be chaper than new OEM sensors, if you feel like doing the mechanical
bit yourself.  If you are doing an EFI circuit board, consider mounting the
sensor right on your PCB.  Vacuum hose doesn't pick up noise, whereas a
wiring harness might... One tip on these, the hose barbs provided on the
sensor are relatively fragile, one slip when pushing on the hose and it's
history.  Better to plumb this out to an external metal hose barb on the
box, to avoid the chance of breaking off the tit.

>Now, which to use -- and what does one do with the data re EFI ??
>Now, the frequency output of the OEM unit -- seems that
>that would entail either an F-V convertor and then A-D or an
>interrupt driven timer circuit that would return a number of counts
>proportional to the period of the sensor output.  Any suggestions?

Either unit will give you equivalent results, and probably don't require any
intervening components to interface to the processor.  If you have enough
analog channels on your micro, analog is probably easier.  If you are short
on analogs, and feel confident that you can write the code to measure
frequency (piece of cake on an 'HC11, but then so is analog) do it that way.
The frequency approach may have better noise immunity than analog.  Forget
the F-V stuff, it's not necessary or desireable.  For dinking around
purposes, you may be better off to get a used unit from an auto wreckers,
and see if it does what you want.  As far as what to do with the data once
you've got it, stay tuned...



regards
dn
dnorquay at awinc.com