# First Circuit - 1st post - Need a hand

#### trope

Aug 9, 2011
12
I am trying to build, and understand this simple lie detector from Kipkay.

I am a newbie to electronics, however, I have been a PHP/mySql programmer for many years, and tech logic is not new to me.

That withstanding, I have a ton of questions about this simple project, which I will attack slowly.

First and foremost is, can anyone explain to me what role the capacitor in this circuit plays?

And lastly, let's say I was the original designer of this circuit, how would I conclude that the transistors and capacitor in this circuit would be appropriate?

I realize this is a 'large' question, but I have been reading ALOT. So, just a high level explanation would be very appreciated.

Thanks! Glad to be on board here!

Trope!

#### Attachments

• newKipKayLargerVersion.png
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#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,507
It essentially converts the resistance of your skin to a tone (with decreasing resistance producing an increasing frequency tone.

When you lie (presuming that this is stressful) you sweat a little more and your skin resistance goes down.

It is a crude and ineffective technique especially if you have someone holding the electrodes (because the resistance will vary strongly with the grip you have on them)

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