DIY Continuity Tester: Increase Sensitivity | Matt

[mattyboson12]

Hello, I'm building a homemade continuity tester from the schematic below, and I want to bump up the sensitivity even further so it can detect high resistance objects. What part of the circuit would I have to modify to allow this? Would it be a higher voltage?

Thank you
Matt

 

[berkeman]

That base resistance (1M) looks kind of big. Even for a short from 3V to that base resistor, you only get a 3uA base current. Depending on the current gains of the two transistors, that's likely marginal for turning on the LED. I would go with more like 100k for that input base resistor.

And avoid using yourself as part of the continuity tester. Just hook the two ends of the test piece to 3V and the input base resistor.