Instructables

Fun With a Lie Detector!

Picture of Fun With a Lie Detector!
Is your friend or spouse lying to you? Build this Lie Detector and find out the truth! Great for parties too!

This is the FIRST Lie Detector project on Instructables.

Watch the video and then build it...


 
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Step 1: Parts you will need...

Picture of Parts you will need...
I picked up all of the components at Radio Shack except for a few I list at the end.

1. Project Enclosure
2. 4.7K Resistor
3. 82K Resistor
4. 0.01uF Capacitor
5. 2N3904 Transistor
6. 2N3906 Transistor
7. 2-AA Battery holder
8. Small circuit board

Spare PC speaker, velcro, aluminum foil, wire and AA batteries in my extra parts bin.

Step 2: Basic Tools...

You will need a soldering iron/station, solder, screwdriver, hot glue, small drill bit and wire strippers.

Step 3: Build the circuit...

Picture of Build the circuit...
Following the schematic shown here, build the circuit. Take your time and make good solder joints.

Step 4: Make the Finger Pads...

Picture of Make the Finger Pads...
Install everything in the project enclosure leaving just the Finger Pad leads exposed through drilled holes. I also drilled holes in the box so you can hear the speaker.

I got the finger pad design from this article.

Using a strip of Velcro (soft side), cut a piece of aluminum foil the size of the veclro. Make sure the velcro is long enough to go around a big, fat finger. Some liars are chubby. Remove the sticky side of the velcro and attach the aluminum foil with one of the Finger Pad leads under the aluminum. Then use a smaller piece of the other part of the velcro (the 'hook' side) and attach it to the end so the whole pad can be wrapped and secured.

Step 5: Test it out...

Picture of Test it out...
This works on the galvanic skin response. When you lie, your skin becomes moist. While this does work, it's not as accurate as a true Polygraph machine. Hope you enjoyed this Instructable and for another really good DIY Lie Detector, check out Jason Bradbury's!
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ETfonehome1 year ago
How do you tell if someone is lying to you? Does the speaker change tone or something like that?
punom3 years ago
where the R2 resistor ends?
Pienso, que el final de R2 es tu dedo, cuando aterrizas con R1.
It goes to a finger pad. The line sticking out in between C1 and R1 goes to the other finger pad
Kzummo1 year ago
An 82k resistor? Is that what that is? Because it doesn't at all look like it? PLEASE HELP!
I tested this with a breadboard, and when I put on the finger pads the speaker makes noise, but the tone slowly goes up and up and it doesn't stop for, like, 30 seconds. I tried lying with it but the speaker didn't change tone :/
Is there a switch? Or does it turn on when you put on the finger pads?
gmarian2 years ago
What can substitute 2N3906 PNP transistor?
2N3906 are NPN transistors, and no no other transistors can replace it in this particular circuit
rhapsodium2 years ago
great tutorial. used a breadboard instead of a circuit board, worked fine. the computer speaker had too much resistance, though, so i just bought a tiny eight ohm one from radioshack.
hey could i use a breadboard instead of a circuit board to build this?
yes
robofish7232 years ago
Same here, there isn't even a peep coming from the speaker, anyone haveany help?
mshahzeb3 years ago
i have same problem no sound is coming from speaker.
raza8963 years ago
Will it help to catch the 9/11 attackers??????????
acaz936 years ago
Hey , Kip .. Remember The Comment That Says It needs a tuning pot It's actually simple , just put (instead of 82k resistor ) a 50K Potentiometer and a 33k Resistor In series , And That's It , VOILA tuning ready!
can you get the pentiometer thingy at radio shack as well as the 33K resistor? its kind of convenient I read now cuz thats the one thing i don't have yet! lol!
Yes You can , but it is not vey cheap :S ,
Here are the links by the way 50k Pot And 33k Resistor
acaz93 acaz936 years ago
resistor's color code is Orange-Orange-Orange-Gold
resistor 01.jpg
Kaiven acaz936 years ago
you know about electronics? i know how to make a tazer from a camera, and found it only gvies 35v. I saw at radio shack a huge capacitor that was 500v. could i replace the 35v with the 500v capacitor? would i need multiple camera boards to sharge it? thanks
XOIIO Kaiven3 years ago
It actually isn't technically a tazer, it is far from it, and the capacitors in cameras are usually 200-450 volts.
Actually, they put out 350 Volts, not 35. Check the current on the 500V cap and make sure you dont kill anyone. the little camera circuit should charge it just fine, just make sure you have your polarity right. It might take a little bit longr to charge but hey, if it keeps em' twitcing!
ahh... okay then....how do i check the current?
I think amperage is the same as current but im sure some other guy reading this is gonna tell us otherwise, but check that with a volt meter, it might be under Ohm's as well, thats current im sure... and besides amps can be lethal too. Let me guess your age... 9-11?
my age ? i'm 15
Current is checked using an Ammeter (or use the Amp function in your multimeter)
just remember more than 900 mA = Semi-lethal shock
You're still a smidge off on your digits, I'm pretty sure its just 90ma for death...
bye the way, i was actually talking to cowscankill on the whole age thing.
haha! im twelve, though ussually i think im thirteen. i don't have any a-meters of any kind. maybe i could shock metal and see which leaves a bidder mark?
Stuffses Kaiven4 years ago
 woo! teens are smart too! im 13 and im buildin a combat robot with a coilgun.
Kaiven Stuffses4 years ago
 I'm actually 15 now lol. But I do love weapon design...
that would be really primitive most all multi meters have amp reading
ok , i understood
The FCC ham test thing says 100 mA
I Think you're Right , Actually Less Than 7 mA Can severely injure somebody , Awww , Science ...
Stuffses acaz934 years ago
 i thot it was more than 10mA
acaz93 Kaiven6 years ago
Well , Just A little , i'm actually a student It's kind of hard , for example , your camera board gives 35 v , it actually shocks you beacuse of amperage not voltage , a simple solution if you have a AC source , you can google "voltage Doubler " Or even better Voltage "tripler " I know how to assemble a Shock Box (giggles lolz) if i just can only find the schematic , gimme a couple of days , I hope this small information helped you
Kaiven acaz936 years ago
hmm...okay thanks, but you say the camera board charges up to 35v? does that mean it wouldn't charge the 500v capacitor?
and yes it would charge the cap but only you would get about 300v not 500v
ok on a disposable camera board when you press the charge button it takes a 1.5v batter and runs it through a small style transformer and the output which goes to the capacitor which is about 300v it varies from transformer to transformer and will not kill you but will hurt alot
acaz93 Kaiven6 years ago
Maybe , The capacitor is just charged half , i actually don't know that much electronics , If its AC the capacitor Is being loaded with about 60 - 75 volts ,maybe...
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