Help with a low resistance meter

[mevrocket]

Hi all
new to the forum and not the best with electronic.. altho im not to bad at soldering and deciphering diagrams.. i just have no idea with the techie side of things.

id like some help if possible from one of the Electronic wizards here..

id like to make a simple circuit that will light up an led when the resistance in the circuit falls below a 100 ohms. or a circuit that i can adjust the resistance that triggers the LED

the circuit will be powered by a 12 volt car battery

thanks
Paul

 

[Harald Kapp]

You want a continuity tester with a treshold of 100 Ohm.

Look here: http://www.extremecircuits.net/2010/04/continuity-tester-circuit-diagram.html
This circuit probably works from 12 V, too.
I don't think the type of OpAmp is very critical. If you want to / have to use another OpAmp, just make sure it operates from a 12 V (9V) single supply. The threshold for continuity/discontinuity detection should be adjustable by the potentiometer.

Harald