Help with understanding a lie detector

[NorseViking]

Hey guys, I need some help to understand the composition of this circuit.

The circuit is made by Kip Kedersha, and is found **broken link removed**.

This is the circuit:
**broken link removed**
**broken link removed**

I'd like to know how the resistors and the capacitor effect the circuit, and how these components and the transistors react differently to dry and sweaty fingers, and how it becomes the difference between sound and no sound. (The thing about this circuit is that what it really does is only to react depending on whether the person sweats, in which case it conducts electricity better, which will cause the lamp or speaker to make a sound or light.)

I do know the basics of the physics behind how each component work, though this circuit as a whole I am really unsure of.

Sorry for being rude, but if I can get any help I'd love to get it today.
Any help is appreciated

 

[colin55]

The circuit is a high gain amplifier.
If it were drawn with a proper layout, it would be easy to see how the circuit works.
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The circuit does not turn on until a resistance is created at the terminals.
When this happens, the voltage on one end of the capacitor rises and this raises the other end.
This creates a current through the capacitor and the same current flows through the base of the second transistor.
This causes both transistors to turn on more and the effect keeps happening until both transistors cannot turn on any more.
The value of the capacitor determines how long it takes for this action.
When both transistors are fully turned on, the capacitor keeps charging and the charge-current reduces. This causes the second transistor to turn off slightly and the two very rapidly completely turn off.
The charge on the capacitor is removed via the base of the second transistor and the resistance of the finger starts to charge the capacitor to repeat the cycle.
The resistance of the finger determines the time it takes to charge the capacitor and this creates the frequency of operation of the circuit.

 

[audioguru]

It is not a lie detector. Instead it is a skin resistance measurer. Some people sweat when they tell the truth. Other people sweat when they lie. Some people never sweat.
Each person has a different skin resistance but the simple circuit does not have an adjustment for the differences.

I think the circuit is a variable frequency oscillator that changes its pitch when the skin resistance and the battery voltage change.

 

[ronsimpson]

I built something like this in school. I called it a pregnancy meter. All my machine did way measure the resistance of the skin on your hand. The boys had hard working hands and high resistance. The girls, having soft skin, have low resistance. If you think the machine might work and you get worried and start to perspire then your resistance goes way down.

 

[audioguru]

One time I went to a fake doctor called a Chiro-Something. The first visit was free.
He positioned probes all over my back and pushed hard on them sometimes. Where he pressed hard his computer showed a "problem" (duh, less resistance).
He asked for $1500.000 FOR "ADJUSTMENTS" TO FIX NO PROBLEM WITH MY BACK.

 

[DerStrom8]

In my opinion, that's a very poor design, even for a simple skin-resistance sensor. The speaker seems quite useless, since there's not much of an oscillation to create a decent sound. If you're dead-set on making a resistance meter, I would recommend using one that utilizes a red LED and a green LED. One like this will work better for that purpose:

View attachment 63382

That one switches on the red LED when the resistance gets below a certain point (skin gets sweaty, supposedly from lying) and it's a much better indicator.

Regards