Duplicating fuel and oil sender resistances

Question

I have a generator I would like to add remote fuel level and oil pressure displays to. The senders feed into a DGC-2000.

My original idea was to plug the existing oil and fuel signals into an Arduino, have it display on a screen, then somehow duplicate these resistances to feed into the generator so it doesn't generate crazy alarms.

The fuel sender is a 33-240 ohm sensor and the oil sender is 0-90 ohms. I was thinking of either using a programmable potentiometer or stepper motors attached to physical knobbed potentiometers but I am afraid too much current would pass through these (33ohms at 12V is 363mA, which would be 4.36W dissipated through the potentiometer.)

Is there some way I can do this, or would the current passed through these not be that high?

Answer 1

Any time you retrofit an existing system there's some guesswork involved.

A good starting point is to measure the voltage on the sensor. I'm assuming that your generator follows automotive practice and uses chassis for the negative ground. If so, then the gauges either feed a constant current into the sensors and respond to their voltage, or they feed a constant voltage onto the sensors and respond to their current.

Assuming that you have some convenient way of affecting the gas level and oil pressure (or a spare set of senders), turn the thing on, hook up a voltmeter to one or the other, and experiment. Then hook up an ammeter and experiment with that.

Or, better, get yourself a 250 ohm pot and temporarily connect it up in place of one sensor and the other, so you can get all possible values while looking at voltage, current, and the gauge readings.

Take careful notes, plot voltage and current against the actual gauge readings for each sender, then decide -- for each sender -- if you need to read current or voltage. Then find circuits that do that (this is pretty basic metrology stuff, so the circuits are out there), feed the results into your Arduino, and you're all set.

Answer 2

from the manual:

Sending Unit Inputs

• Coolant temperature
  A current of less than two milliamperes is provided to the coolant temperature sending unit. developed voltage is measured and scaled for use by the internal circuitry.
  
• Oil Pressure
  A current of less than 15 milliamperes is provided to the oil pressure sending unit. The developed voltage is measured and scaled for use by the internal circuitry.
• Fuel level
  A current of less than 15 milliamperes is provided to the fuel level sending unit. The developed voltage is measured and scaled for use by the internal circuitry. Speed Signal

it sure looks like you could also measure the voltage developed at the input terminal and use that as your signal.

with a 15mA signal if your input takes 150uA it will disturb the reading by about 1%.

Arduino ADC inputs take only 1uA so yeah, measuring voltage should basically have no effect on the running of the generator.