DIY Continuity Tester: Increase Sensitivity | Matt

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SUMMARY

The discussion focuses on enhancing the sensitivity of a DIY continuity tester by modifying the circuit's base resistance. Specifically, a participant suggests replacing the 1M base resistor with a 100k resistor to increase the base current from 3uA, which is insufficient for reliably activating the LED. Additionally, the discussion advises against using the tester with the human body as part of the circuit, recommending a direct connection to a 3V power source instead.

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mattyboson12
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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
 

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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.
 
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