Non-Contact Probe Works Better with a Little More Complexity

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Non-contact voltage probes have been around a while and some test equipment now has them built-in. This is one of those things that you probably donā€™t think about much, but surely it isnā€™t that hard to detect AC voltage. Turns out there are a lot of circuits floating around that can do it and [nsievers51] tried a bunch. Many didnā€™t work very well, but the best used a 4069 CMOS hex inverter. A dollar store flashlight provided power, a case, and an LED and the result was a good-looking and effective probe.

The circuit came from the Electronics Library website and is fairly complex for this sort of device. The CMOS inverters have a high input impedance so they pick up the weak signal. Instead of directly driving an LED, two inverters form a ring oscillator that generate pulses around 1 kHz. At that frequency, the LED appears to be on, but battery consumption is less severe. A single 2N2222-style transistor drives the LED.

Weā€™ve seen a number of variations on this tool in the past. Many of them only use transistors.



from Blog ā€“ Hackaday https://ift.tt/NfHXo5F

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