mains hum and static electrocity detector

[neazoi]

Mains hum and static electricity detector

Hello,
I consider this little circuit to detect static electricity and mains hum.

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]

The circuit seems a little strange. Why to you want to detect static electricity and mains hum?

 

[neazoi]

The circuit seems a little strange. Why to you want to detect static electricity and mains hum?

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.

 

[triac]

neazoi, change design.
I did once similar with FETs, and it worked too well.
The simplest example you can see here: http://amasci.com/emotor/chargdet.html

 

[chuckey]

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

 

[schmitt trigger]

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.

 

[betwixt]

...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.

 

[andre_luis]

Re: Mains hum and static electricity detector

...what if I need a little bit more sensitivity?...

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

....I did once similar with FETs, and it worked too well...

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