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Lie Detector Circuit with Motor Possible?

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rockfan0005

New Member
Hi guys,

I've been wondering how to build a lie detector and did a bit of research on the topic. I was able to find a few ideas that were based off of the galvanized skin response (you sweet when nervous). The idea behind this is the more your swetting the better of a circuit you make (or something like that).

Anyway I was able to piece together a few different ideas. Keep in mind I have never done stuff like this but am very interested in trying to make one by hand.

Here's someone's project
Making the lie detector

I'm pretty sure following the directions that I would no problem making that, but that and pretty much all projects I've seen really on a speaker (which seems less reliable). I wanted a way to measure it more accurately. On one project I saw someone said:
"Really like the enclosure, but it'd be really cool to make an arm swing or something when it's picking up on a "lie" Add another transistor, a D/C motor, a 555, a rubber band, a coat hanger and a pencil!"

Is that really possible and if so could make a diagram or something. I figured it was simple compared to some of the stuff others do. If I had any idea of how to do this kind of stuff I'd do it myself, but as is I've got no experience.

Thanks in advance.
 

Willbe

New Member
Before you have it control a weapon, like a big hammer, look up false positives, false negatives, specificity and sensitivity.:p
 

rockfan0005

New Member
Actually the idea was to have it have a pencil write on paper not to hurl the thing a the person taking the test haha. I'm well aware they're not that reliable. I just wanted to have a more reliable method.
 

audioguru

Well-Known Member
Most Helpful Member
The circuit you found is a cheap toy for children.
It is not reliable enough to be a lie detector.
 

Sceadwian

Banned
The only current method of lie detecting that actually works is functional MRI imaging, and even that is open to interpretation.
 

Willbe

New Member
I took a lie detector test for an unnamed US agency, and the test giver lied to me. :eek:
Since then whistleblowers in that same agency have made the news. :D
 

Sceadwian

Banned
Yeah, that's the problem with governments that have power. Not so much the government itself but bad people in it.
 

rockfan0005

New Member
audioguru-yep it's a cheap toy for children, but it's also one of the 3 main components in real polygraph machines. Though I do realize this is quite a bit less accurate then even the worst of professional equipment. This is a fun project-not something I plan to use professionally.

sceadwin-well it depends on what you mean by works. From what I remember polygraphs are reported to be 85% accurate. Yes, they can be wrong and yes you can be trained to fool them but the vast majority of cases they prove to be accurate. Plus again, this is for fun, not something I plan to do interrogations with.
 

tcmtech

Banned
Most Helpful Member
[/QUOTE]the idea was to have it have a pencil write on paper not to hurl the thing a the person taking the test [/QUOTE]

You just invented the perfect lie detector! Make it just look like it was going to do something very bad to you! Then tell the person being tested that it will! ;)
If the potential harm related to lieing is bad enough the machine would never actualy need to be turned on. :eek:
The person would just be afraid enough to be willing to tell the truth! :)
 

audioguru

Well-Known Member
Most Helpful Member
audioguru-yep it's a cheap toy for children, but it's also one of the 3 main components in real polygraph machines. Though I do realize this is quite a bit less accurate then even the worst of professional equipment. This is a fun project-not something I plan to use professionally.
It uses the resistance of a person to change the pitch of its oscillator.
You need a circuit that uses the resistance of a person to change its output voltage then amplify the output voltage to drive your motor.
It also needs to have a voltage regulator because now the output changes as the battery voltage runs down.
 

Sceadwian

Banned
Even then it still doesn't work to detect lieing =)
 

trident9

New Member
rockfan0005
What you are looking for may be a pen motor, I recall seeing one in 'The Amateur Scientist' section of Scientific American many years ago. It was very large and somewhat crude. A more reasonable option could be to salvage one from an old Honeywell chart recorder.
______
trident
 

Sceadwian

Banned
If it's consistently the result of lieing then why are the results inaccurate? Lie detectors DO NOT WORK, in the US they're explicitly banned from being entered into evidence because there has never been a strong enough correlation to warrant their use as scientific evidence.
 

audioguru

Well-Known Member
Most Helpful Member
Many people lie all the time. They sweat when they tell the truth and make a lie detector useless.
Some people never sweat.
 
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