Activate a circuit based upon ohm value

[rwp289]

I work with cars and would like to add a warning light to fuel, oil pressure and water temperature circuits that have gauges but no warning lights. Most gauges signal via a chaging ohm value. For instance a fuel level gauge will read full at 100 ohms and empty at 10 ohms.

I would like to know if there is a resistor, diode, etc. that could be used to read the ohm value and "turn on" or "turn off" based upon an ohm value. In the case of the fuel gauge example, say at 20 ohms. Then I could add light or LED as a warning without the need for an additional sending unit or sensor.

Ideas?

Thanks

 

[IanP]

If you connect a voltage comparator to the fuel gage you can set threshold points where the voltage comparator will switch, thus indicating low, or high stage of the fuel-level sensor ..
The same can be done with oil pressure, water temperature etc. etc...

Here are examples based on the LM741 op-amplifier [working as comparator] with detailed description:
**broken link removed**

Rgds,
IanP

 

[rwp289]

Thank you for the reply and advice. I am studying the diagram and will let you know how I do.