Haltech f7c map sensor info...

[Chris Conlon]

At 04:11 PM 1/21/01 -0800, Kris Weldy wrote:

>I finally got the info from my haltech map sensor.The goal of this project
>is to change the haltech f7c map sensor(mounted onto the chip)from a 22psi
>map sensor to a 3 bar map sensor(roughly 40psi?).
>
>merely a letter "M" with a circle around it.then follows two rows of number
>below it-the first row of numbers is:
>mpx2200ap
>the second row reads:
>94    40

This is the Motorola MPX2200. The -AP refers to the case style. See:

http://e-www.motorola.com/webapp/sps/prod_cat/taxonomy.jsp?catId=M939346219036

That page lists the Moto sensors in that family, incl. the 2200. You
can d/l the datasheet incl. pinout, etc. 9440 is probably a date code,
40th week of 1994.

The bad news is that this is an non-signal conditioned sensor, which means
you can't just drop in a normal 3 wire, +5v conditioned output sensor. It's
a raw bridge. It takes a drive V from 10-16V and outputs a low level
signal, ~40mv full scale.

Moto does not seem to offer a similar unit above 2 bar. (The MPX2200 is a
2 bar absolute unit, good up to ~14.5 psi of boost.)

The ideal would be another sensor that's electrically similar, but which
reads 3 bar at a nominal 40mv output. Somebody out there may have one,
time to hit the catalogs and websites.

A less ideal solution would be to build a little circuit to regulate
the sensor drive down to +5v, drive a normal 3 wire conditioned unit,
and use a voltage divider to cut it's output down to 40mv full scale.
You'd also need to convert that signal into a fake differential signal,
roughly in the middle of the V+/ground range set up by the sensor
drive voltage. Should be the work of a few resistors and op amps,
but you'll need good precision parts for the resistive divider, noise
may be a problem, accuracy may suffer, etc. (Insert the usual EE
booga-booga warnings here.)

A quick look thru the Digikey catalog (www.digikey.com) shows that
they offer a few sensors which might be usable. You need one that
outputs 40mv at your desired max boost. The promising ones look like
100mv FS at 100psi (absolute). This will deliver 40mv (the full scale
the Haltech will "see") at 40psi. This is p622-624 of the Oct-Dec 2000
catalog, SenSym and Measurement Specialities. Prices range from $25 to
$100++.  You also need to make sure the new sensor can handle the
voltage (MPX2200 is listed at 16v max, or you could measure what the
Haltech is actually providing), and that the bridge resistance is
ballpark similar.


>3 bar sensor i can use to replace this one?Someone also said the software
>would change if i changed the map sensor-i got the impression they were
>implying that the motherboard would "know" and then the software would go up
>to the 3 bar setting.Is this true?

It won't know by itself. There may be a software setting where you can
tell it, but if the swap is done right the box will have no idea what
was done.


   Chris C.

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