Simple Lie Detector

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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.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	33K 1/4W Resistor
R2	1	5K Pot
R3	1	1.5K 1/4W Resistor
C1	1	1uF 16V Electrolytic Capacitor
Q1	1	2N3565 NPN Transistor
M1	1	0-1 mA Analog Meter
MISC	1	Case, Wire, Electrodes (See Nots)

Notes

The electrodes can be alligator clips (although they can be painful), electrode pads (like the type they use in the hospital), or just wires and tape.

To use the circuit, attach the electrodes to the back of the subjects hand, about 1 inch apart. Then, adjust the meter for a reading of 0. Ask the questions. You know the subject is lying when the meter changes.

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Comments

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T.Jackson Simple Lie Detector Sunday, August 29, 2010 3:17:11 AM

How this circuit works: This ciruit works by detecting changes in a person's conductance. Our body always conducts (n) degree electricity, and when there is moisture (sweat in this case) -- this degree of condcutance increases. When a person is lying, their body produces sweat, and this circuit picks up on this. This circuit could also double as a liquid detector too.

anonymous Simple Lie Detector Tuesday, June 29, 2010 9:05:52 AM

Does not work...

anonymous Simple Lie Detector Friday, June 18, 2010 3:37:43 AM

cant you have an explaination to the cct. on this page too an dhas anyone tried and tested this one yet?

trinath Simple Lie Detector Saturday, May 22, 2010 1:43:38 PM

how this lie detector works without LED's

manish Simple Lie Detector Tuesday, March 23, 2010 4:51:53 AM

can we replace 2n3565 by 2n3522 ????????

haert Simple Lie Detector Tuesday, March 09, 2010 6:04:15 PM

Does the M1 meter get adjusted for each use or do you adjust the R2? Also is M1 needed or can you just replace it with LED's for indication?

dipa Simple Lie Detector Thursday, January 28, 2010 4:14:10 AM

I maid this project but it does not work.Please tell me how does it really work.

Naomi Hays Simple Lie Detector Tuesday, January 26, 2010 5:11:45 PM

Can you put step by step directions on how to build this or can you send it to me in an email because i am building a lie detector test for science fair and i don't understand this picture (p.s. i'm only in 8th grade). So can you please do me a favor and simplify this? Thank You

namit Simple Lie Detector Tuesday, January 19, 2010 11:45:49 AM

should have seen this much more earlier

vineeth Simple Lie Detector Tuesday, January 05, 2010 10:15:50 PM

is the analog meter AC or DC

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T.Jackson	Simple Lie Detector	Sunday, August 29, 2010 3:17:11 AM
How this circuit works: This ciruit works by detecting changes in a person's conductance. Our body always conducts (n) degree electricity, and when there is moisture (sweat in this case) -- this degree of condcutance increases. When a person is lying, their body produces sweat, and this circuit picks up on this. This circuit could also double as a liquid detector too.
anonymous	Simple Lie Detector	Tuesday, June 29, 2010 9:05:52 AM
Does not work...
anonymous	Simple Lie Detector	Friday, June 18, 2010 3:37:43 AM
cant you have an explaination to the cct. on this page too an dhas anyone tried and tested this one yet?
trinath	Simple Lie Detector	Saturday, May 22, 2010 1:43:38 PM
how this lie detector works without LED's
manish	Simple Lie Detector	Tuesday, March 23, 2010 4:51:53 AM
can we replace 2n3565 by 2n3522 ????????
haert	Simple Lie Detector	Tuesday, March 09, 2010 6:04:15 PM
Does the M1 meter get adjusted for each use or do you adjust the R2? Also is M1 needed or can you just replace it with LED's for indication?
dipa	Simple Lie Detector	Thursday, January 28, 2010 4:14:10 AM
I maid this project but it does not work.Please tell me how does it really work.
Naomi Hays	Simple Lie Detector	Tuesday, January 26, 2010 5:11:45 PM
Can you put step by step directions on how to build this or can you send it to me in an email because i am building a lie detector test for science fair and i don't understand this picture (p.s. i'm only in 8th grade). So can you please do me a favor and simplify this? Thank You
namit	Simple Lie Detector	Tuesday, January 19, 2010 11:45:49 AM
should have seen this much more earlier
vineeth	Simple Lie Detector	Tuesday, January 05, 2010 10:15:50 PM
is the analog meter AC or DC