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Circuits: WTF is this?

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Sumguy

Sumguy

Golden Member
emf.gif


Anyone know whats going on with the 2.2M resistor? Why is there a circle near it, and why does it have a loop?
 
grrl said:
Is it a potentiometer?
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yeah it's a potentiometer. the circle probably denotes clockwise

the loop means the wiper is connected to one of the other terminals.
and the loop is connected to the output of the opamp.
the last terminal goes to the 10k resistor.

it's there to change the gain.
 
Last edited:
Its likely a 10 turn trim pot. This is a crude amplifier, that is probably not good for much, as it uses an antiquated 741 op amp. It has a DC gain of 0 and an AC gain of about 100. 741s are not really good at single supply mode, but this circuit is biased as such, even though it has a split at the non-inverting input. Not sure what the coil represents as a probe.
 
Electromagnetic Field Detector

emf.gif


This circuit is sensitive to low frequency electromagnetic radiation and will detect for example hidden wiring or the field that encompasses a transformer. Pickup is by a radial type inductor, used as a probe which responds well to low frequency changing magnetic and electric fields. Ordinary headphones are used to for detection. The field that surrounds a transformer is heard as a 50 or 60Hz buzz.
Click to expand...
 
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