At 01:20 AM 6/05/98 EDT, you wrote:
>Hello everyone
>
>I want to drive the OEM fuel gauge used on most common vehicles. Current
>gauges use a resistive device to ground to drive the gauge, for example most
>Chevy use a 0-90 ohm sender ( 0=full, 90=empty) , Ford 160-10 or 70-0 ohm and
>a few others.How can I use a stamp or PIC to drive these gauges. I was
>wondering if I could use PWM to drive the gauge to ground? I could utilize a
>different table for each vehicle type. Any suggestions on how I might
>accomplish this. Feel free to offer other suggestions I don't know if PWM will
>work, but I am sure someone out there has figured out a slick way to do this.
>
>         Gauge----------------Sender-----------GND
>
>Thanks in advance
>
>Jon
>
>

Are!
Question and answer time,
1/      What are you using as the input? The fuel sender?
2/      Are you trying to drive the actual gauge? (Some form of common device)

I assume that this is correct from your comments, however the gauges that
you wish to drive seem a bit old hat. At present many instrument cluster
manufactures are using stepper motors to drive the gauge (The GMH VT Commode
is an example of this) Chrysler also don't use a resistive sender (This has
caused them countless troubles, I think that there up to Version 3 on the
Jeep!) Ford Australia also don't use a purely resistive sender. The reasons
for this are current consumption.

In the "normal" older style installation one side of the gauge is connected
to +12V and a basic resistive divider forms the sensor /sender (The gauge is
a  damped current meter). To do what you want a simple FET that connects +
of the gauge to ground could be used, then you suggestion of PWM to the gate
could be used (With the damping of the gauge). I do suggest that you filter
the PWM before it goes into the FET as it may induce noise (Not very likely
in such a low current situation) into other circuits of the auto. You will
also proberably need some feedback to compensate the FET. This is the
simplest solution that I can think of, there are others (As usual) that are
technically nicer, but this should work. Hope that it helps.


Dennis