Do the math for putting a 1K digital pot in parallel with a 27 ohm=20
resistor.  I don't trust my quick try which says the pot should vary=20
from 77 to 338 ohms, which would not be a resolution problem, would it?
Joe W


On 5/11/2012 5:55 PM, Cristiano Cesaretto wrote:
> Hello.
>
> I am building my racing simulator and I want to use a real fuel level and
> water temperature gauges.
> I would like your opinion about  which way to drive these gauges is the
> best. Sorry if I say somethig silly but my knowledge is limited.
>
> So the gauges have 3 wires: 12V, ground and the signal.
>
> http://dl.dropbox.com/u/3544050/gauge1.GIF
>
> the signal connects to the sender that converts the fuel level or water
> temperature in a variable resistance. the resistance varies from few Ohm
> until 20-25 Ohm.
>
> my doubts regard how to generate the variable resistance.
> I have three options in mind:
>
> 1) using a digital pot. the smallest pot I can find is 1KOhm so resolutio=
n
> could be a problem. I think I can solve putting a resistor in parallel.
> 2) I read I can use a mosfet as a variable resistor.I have never done tha=
t
> but I will investigate it
> 3) I have replaced the variable resistor with a mosfet and applied a pwm
> signal to the gate. it works but the gauge because noisy, it makes a soun=
d
> like BUZZZ...
> also on the drain I have voltage spikes up to 120V. I suppose because the=
re
> is something inductive in the gauge...
>
>
> Does anybody have suggestions or consideration to make?
>
> Thank you
> Cristiano

--=20
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