# How does this work

#### SgtWookie

Joined Jul 17, 2007
22,210
I already explained how the circuit works.

It's an oscillator. If the resistance between the probes decreases, the oscillator increases in frequency.

You already have more than one thread going on this same topic.

#### asdff1818

Joined Dec 7, 2009
35
I already explained how the circuit works. It's an oscillator. If the resistance between the probes decreases, the oscillator increases in frequency.
I know but I need more help, please help cause it is kind of hard for me and I want to understand it part by part.

You already have more than one thread going on this same topic.
I know, but they are all about different things/questions, one is about the ohm meter, the other one is about the transistors, and this one is how it works part by part, please help me understand.

Thank You!!!!

#### asdff1818

Joined Dec 7, 2009
35
Sure.
Start here:

When you get done with that volume, go here:

If you don't understand something, go here:

Bon appetit!
Thank you so much! But after I read all of that, will I be able to understand how it works? And also, do I need to read all of that to understand? If not, what parts?

Thank You!!!!

#### SgtWookie

Joined Jul 17, 2007
22,210
Thank you so much! But after I read all of that, will I be able to understand how it works? And also, do I need to read all of that to understand? If not, what parts?
You obviously want to know how the circuit works in detail, and how to understand each of its' component parts, and how they function, and what part they play in the circuit.

If I took the time myself to do all of that, the next time you needed to know something, you would need more explanations on how they worked, too.

If I gave you a fish, you would eat today. Tomorrow, you would need another fish.

#### asdff1818

Joined Dec 7, 2009
35
You obviously want to know how the circuit works in detail, and how to understand each of its' component parts, and how they function, and what part they play in the circuit.

If I took the time myself to do all of that, the next time you needed to know something, you would need more explanations on how they worked, too.

If I gave you a fish, you would eat today. Tomorrow, you would need another fish.

Thank you, I will read that. But just to make sure, after I do read it, will I be able to understand it part by part?

Thank You!!!!

#### SgtWookie

Joined Jul 17, 2007
22,210
Thank you, I will read that. But just to make sure, after I do read it, will I be able to understand it part by part?
That depends upon how hard you study the material presented, and how well you remember it.

#### asdff1818

Joined Dec 7, 2009
35
Thank you, but since I am new to this forum, is there a best answer button or anything like that?

Thank You!!!!

#### asdff1818

Joined Dec 7, 2009
35
I understand each part of the circuit, but I don't understand how it all comes together. I understand about the transistors, resistors, and the capacitors, but I don't understand how the circuit its self works and come together. I need help with that

Thank You!!!!

#### SgtWookie

Joined Jul 17, 2007
22,210

"Rbody" will change (decrease) when a person perspires (sweats). Usually, if someone's lying, they'll start to perspire, so the resistance of the skin will go down.

This causes the oscillator to increase in output frequency.

R1 and Rbody conduct a very small amount of current which charges the lower side of C1 to be more positive, until the base of Q1 rises above about 0.63v via R2. When that happens, Q1 turns on, and pulls the base of Q2 low, which charges the high side of C1 causing Q1 to momentarily turn fully on. At the same time, the voltage across SPK1 rises sharply.

As C1 is discharged via R2 through the base of Q1, Q1's base current drops off, turning Q1 off. This turns off Q2, and the voltage on the speaker is removed. C1 then starts charging up again via R1 and Rbody, and the cycle repeats.

The circuit produces a sound that varies in frequency depending upon the resistance of Rbody.

I don't know how much more clearly it can be explained.