Simple Lie Detector - Page 4 - Electronic Circuits Projects Diagrams Free

kambliarup · 20th August 2006, 03:50 AM

Impressive Post

rishirajarora · 23rd August 2006, 08:07 AM

Quote:

Originally Posted by ElectroMaster

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** · 23rd August 2006, 09:13 AM

Quote:

Originally Posted by rishirajarora

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 · 6th September 2006, 01:24 AM

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

muki55 · 6th September 2006, 01:28 AM

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

audioguru · 6th September 2006, 02:12 AM

Quote:

Originally Posted by coolboy8505

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 · 1st October 2006, 12:27 PM

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 · 1st October 2006, 04:00 PM

This simple circuit will work with any little NPN transistor.

weegee · 3rd October 2006, 02:16 PM

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 · 9th October 2006, 11:02 AM

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 · 9th October 2006, 02:05 PM

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 · 9th October 2006, 07:29 PM

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 · 9th October 2006, 07:40 PM

Quote:

Originally Posted by LeeMorgan

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 · 9th October 2006, 08:53 PM

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 · 9th October 2006, 08:57 PM

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

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20th August 2006, 03:50 AM	(permalink)
kambliarup	Impressive Post

6th September 2006, 01:24 AM	(permalink)
muki55	Cool!!!!!!! Thanks for the great idea.

6th September 2006, 01:28 AM	(permalink)
muki55	Its better to use analog meter w/ needle in the center

1st October 2006, 12:27 PM	(permalink)
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...

1st October 2006, 04:00 PM	(permalink)
audioguru	This simple circuit will work with any little NPN transistor. __________________ Uncle $crooge

3rd October 2006, 02:16 PM	(permalink)
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?

9th October 2006, 11:02 AM	(permalink)
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. __________________ If is too complicated.....most of the times is the wrong way.

9th October 2006, 02:05 PM	(permalink)
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. __________________ Don't make me reach through this monitor to slap you a good one!

9th October 2006, 07:29 PM	(permalink)
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

9th October 2006, 08:53 PM	(permalink)
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?

9th October 2006, 08:57 PM	(permalink)
audioguru	Your class doesn't need any power supplies. An ordinary little 9V battery can be used. __________________ Uncle $crooge