Care !!
Don't know if this is a modern car.
Some older designs use a "gauge voltage regulator" which is a bimetallic
strip voltage regulator (believe it or not) which applies PWM output at
about 1 Hz rate :-) and gauges have sufficiently low time constant to ignore
this. This overcomes dependency on battery voltage. Trying to understand
what was going on if you hadn't met this arrangement may be interesting.

I imagine this arrangement is not used in modern cars :-)


      Russell McMahon
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-----Original Message-----
From: Mark Willis <            >
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Saturday, 22 July 2000 10:51
Subject: [EE]: Auto fuel gau    ge monitor


>Have something going on weird with the fuel gauge on one car.
>
>Want to see what's up voltage-wise on that line, using a PIC.
>
>Last I looked at this sort of thing, the gas gauge sensor is a pot from
>12V to ground, so you get a fairly high impedance signal coming from
>that line, & the gas gauge is basically a somewhat low-current
>voltmeter, right?
>
>(The gauge sometimes works just fine, sometimes wanders all over the
>place, just want an idea of what's going on there, hopefully without
>having to drop the gas tank.)
>
>  Mark
>
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