Simple Lie Detector

[haka]

someone can telling me how does it work? cos i not so clear about it working.. hehe..
can use msn chat with me?
ljung_ng@hotmail.com
thx...

read the first post

cos i still not sure for it circuit.. so any1 can helping me?

 

[akg]

cos i still not sure for it circuit.. so any1 can helping me?

it just measures/ shows the variation in the skin resistance(aka galvanic skin resistance) .when we lie , biological changes occur in our causes perspiration , so that the skin resistance goes low .

 

[Elektrohead]

Hi all, Noob here, just wondering if you can tell me what size wire I need to use?
I have some 30awg solid, will this work? Thanks

 

[Roff]

Hi all, Noob here, just wondering if you can tell me what size wire I need to use?
I have some 30awg solid, will this work? Thanks

Yes. It needs to be insulated except where connections are made.

 

[Elektrohead]

Cool, thnx Ron.
I'll post a pic once I am done and get it working.

 

[kambliarup]

Impressive Post

 

[rishirajarora]

Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie.

hi.i hav made this project but i hav used power transistor BD115 instead of 2N3565.Can u tell me whether it is ok or not and if not please tell me the transistor as 2N3565 is not available in the market

with regards
Rishi Arora

 

[Nigel Goodwin]

hi.i hav made this project but i hav used power transistor BD115 instead of 2N3565.Can u tell me whether it is ok or not and if not please tell me the transistor as 2N3565 is not available in the market

I wouldn't have thought it suitable? - you just need a general purpose small NPN transistor - NOT a power transistor, it will have too low a gain.

Try a BC109, which should be ideal!.

 

[muki55]

Cool!!!!!!! Thanks for the great idea.

 

[muki55]

Its better to use analog meter w/ needle in the center

 

[audioguru]

Sry, can anyone tell what is Electrodes?

The electrodes are the parts of the circuit that touches your skin for the circuit to measure the resistance.
Electrodes are usually made from rotting dead fish, aren't they?

 

[sahil_maratha]

Thanks for giving this valuable and simpe circuit. But I am unable to get this transistor . Can u think this will work with any other transistor like BC 548 or simply tell me about the equivalent. Thanks again...

 

[audioguru]

This simple circuit will work with any little NPN transistor.

 

[weegee]

what mods would i need to do, to measure this as a voltage on my sillyscope??

Is it just a case of putting a load resistor in place of the meter, and probing either side with the scope?

 

[Tarsil]

Made the circuit ...it's quite a nice gadget :lol.I used something like 0.5X2.5 inches strips of metal (Al) with tape as electrods. I used a 2n4401 transistor.
I already cought my girlfriend lying :lol.

 

[HiTech]

Yeah, it's always wise and best to thwart future problems by dumping her now. And to think you have a 1-transistor circuit to owe it all to.

 

[LeeMorgan]

Lie Detector Question

Hi everyone -

Just wanted to know why exactly there are two power supplies in the lie detector circuit as opposed to one - what is the function in relation to how this circuit works?

Thanks!
LM

 

[Roff]

Hi everyone -

Just wanted to know why exactly there are two power supplies in the lie detector circuit as opposed to one - what is the function in relation to how this circuit works?

Thanks!
LM

I posted a single-supply version on page 2 of this thread that is identical in function. Here it is again.
The circuit is a Wheatstone bridge.

 

[LeeMorgan]

Hmm...

Thanks for the reply, Ron - I like your schematic alot. My class will be building these and your version will allow us to have smaller groups working on this since we will now have more power supplies to work with. I see how your particular circuit can be re-drawn to essentially be a wheatstone bridge circuit. However, I am still a bit stuck on how the original circuit can be represented this way with those two power supplies. Why did the designer feel that two power supplies were needed in this circuit?

 

[audioguru]

Your class doesn't need any power supplies. An ordinary little 9V battery can be used.