Low Fuel Level Light

Hi guys, I have a turbo drag bike and I have dumped the stock dash for a custom set of gauges. In doing so, I dumped my fuel gauge but kept the sender unit in the tank.

My question is, Can I make a simple circuit to illuminate a LED when the resistance of the fuel gauge sender is 90 Ohm's and greater? I dont want a gauge, I just want to know when I am getting critical low fuel.

The LED will be a 5v 20mA high bright unit and the source voltage on the bike is 12v. I know the resistor needed to protect the LED no probs, its just the switching part I dont get.

I have done a stack of searching on the net but maybe I am not using the correct keywords.

Any help appreciated

You could connect the fuel sender in a bridge resistor circuit and detect the output with a comparator such as the LM339. Google "bridge circuit" and look at the LM339 data sheet for more info. The 339 can only drive a max of 16mA so you would need to add a transistor if you want to drive the LED at 20mA.

Here is a circuit you can use.
You need to know if the fuel gauge is a pot or rheostat to complete the circuit diagram provided.

The sender has only two terminals so doesnt that make it a rheostat?

Does the resistance of the fuel gauge get smaller as the level of fuel gets lower?
Do you want the LED to be off at 100 ohms and on at 90 ohms?

Resistance gets higher as the fuel gets lower. I want the light to be on at 90 ohms and anything greater. The highest the resistance goes is 135 Ohms at bone dry.

Thanks

Here is the circit for your application:

Thanks Colin, youre a legend. I hope to put it together this week so I will let you know how it pans out.