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mains hum and static electrocity detector

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neazoi

neazoi

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Mains hum and static electricity detector

Hello,
I consider this little circuit to detect static electricity and mains hum.
MainsHum-2.gif

I have replaced the transistors to BC549C to get a little bit lower noise and it works ok, but what if I need a little bit more sensitivity?
I was thinking of replacing the first transistor to a germanium one. The germanium transistors have lower base-ON voltage as far as I concern, so the led should light up more easily, yelding in more sensitivity.

What is your oppinion and what kind of germanium transistors to look for?
 

crutschow said:
The circuit seems a little strange. Why to you want to detect static electricity and mains hum?
Click to expand...

A reason could be to find hidden mains cables inside the wall. Another reason would be to detect static electricity before touching the part. It could also be used as a touch switch or transformer EM radiation indicator. Who knows what else, but let's focus on the question.
 

I would connect the highest value resistor you can find (10, 22,33.... M ohms) to the input base and connect the other end to the centre slider of a high value potentiometer, with the other end going to earth and the +6V. Adjust the pot, so the LED is just off.
Frank
 

In other words, what chuckey is saying is to bias the transistor just below the threshold of conduction, such that any stray voltage will push it above threshold and start conducting.
 

...and in any case I wouldn't try Germanium transistors, their higher leakage current would probably hide the charges you were trying to detect. A FET input is the best solution, with a pair of silicon diodes across it's gate and source to protect it and a high value resistor in series with the probe to limit input current.

Vrian.
 

Re: Mains hum and static electricity detector

neazoi said:
...what if I need a little bit more sensitivity?...
Click to expand...

You really could consider the approach suggested bellow.
In the past, I worked with some alarm car systems extremely sensitive to human touch.

triac said:
....I did once similar with FETs, and it worked too well...
Click to expand...


+++
 

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