Simple Lie Detector

[audioguru]

You need a cheap 1mA analog meter movement, not an over-priced old multi-meter. I don't know if anybody sells a meter movement anymore.

You need a linear 5k potentiometer, not an audio one.

The circuit detects that a person is sweating, not lying. Some people lie all the time and do not sweat. Some people sweat when they are telling the truth.

 

[wmmullaney]

Why would little kids want to play with this simple circuit?
Why would anybody want to play with this stupid and simple circuit??

Aw, c'mon audio, why do you think? I'ts so cool, this is a great starter poject.

(Are all Canadians like that?)

 

[audioguru]

The lie detector circuit doesn't detect lieing. It is just an ohm-meter that detects sweating and the amount of pressure on its probes.
If you want to know if somebody is sweating then just look at them, you don't need an stupid simple ohm-meter.

If you want to know if someone is lieing then look on Google at all the things that are needed for experts to guess (frequently wrong) if they are lieing.

 

[Roff]

The lie detector circuit doesn't detect lieing. It is just an ohm-meter that detects sweating and the amount of pressure on its probes.
If you want to know if somebody is sweating then just look at them, you don't need an stupid simple ohm-meter.

If you want to know if someone is lieing then look on Google at all the things that are needed for experts to guess (frequently wrong) if they are lieing.

It is a good idea to warn people that this is really not a lie detector, but it's still a magical little electronic thing that you can build yourself, play with, show your friends, and marvel at what you hath wrought.
Hell, I started out with things as simple as putting a couple of small turns in a piece of copper wire, putting it across a flashlight battery, and wondering why the little coil was the place that glowed red.

 

[kozer]

hi to everyone!!!this is my first post!!!in my school they tell us to make a simple circuit with orcad and i find lie detector a good simple project but i cant find in libraries where M1 and electrodes are...Can you help me by telling me the names of the parts plz...??????

 

[pradeep.durai]

hi it looks cool and it works!!!!!!!!!1

 

[georgie]

i've alrdy know about on this proj...the electrodes are the resistance coming from the tip of the finger...it neutralize how sweat is u'r skin...the more sweat, the more possibility means the person is not telling the truth...^^

 

[Willbe]

Other people don't sweat when they lie

You also might look into false positives and false negatives, test sensitivity and specificity, and Paul Ekman's book on lying.

Took a lie detector test once, and the tester lied to me about the results! I have observed that there is almost nothing that cannot be accomplished by lying.

You can detect lies, but finding the truth is a bit more difficult.

As to "other people", try this. . .
https://www.mcafee.cc/Bin/sb.html

 

[Jerry.J.]

Help with cad Electronic drawing program

Hi from Jerry.J.(Cape Town) Good to be with you guy's!I am 61 years old and wish you all of the best! Been in Electronics and radio.HT,Pic 16f84 for long time.Go for it!You are our future.I am also a radio ham,ZS1JJM and need a electronic drawing progam in order to be able to send you some of my Ideas.Can anybody help with a "ZIP"? Best to u all Jerry.J.My Email:jerryjean@vodamail.co.za

 

[audioguru]

I make all my schematics with Microsoft Paint program.

 

[Roff]

I use LTspice, which is a simulator, but has a pretty good schematic capture.

 

[Leftyretro]

My first project was a D cell, a lightbulb and some hook up wire! I took it to the dinner table with me while I ate! From there I got one of those 200 in one kits and then it was off to the big times: Heathkit HW-101 100 watt SSB transceiver!!

Same here, started with a lamp. Then advanced to a small motor, but would piss off the parents because the brush noise would screw up their TV reception, we were in a fringe area. Then advanced to crystal radios with a long wire antenna. Heathkits were great.

Lefty

 

[Willbe]

Sry, can anyone tell what is Electrodes?

The things on the side of this guy's neck.
http://www.dmiblog.com/archives/Frankenstein_monster_Boris_Karloff.jpg

 

[Willbe]

It's not at all accurate, lie detection is a very complicated subject, and not terribly accurate anyway!.

Even with high accuracy, this concept says you can still be lying, or not.
Sensitivity and specificity - Wikipedia, the free encyclopedia
It gets mathematical, with conditional probabilities.

The way around it is to take several lie-detector/pregnancy/other-medical tests.

I took a lie detector test once. The test-giver was lying to me about the results! (I didn't get the job, either. . .)

 

[Disco Elephant]

I use LTspice, which is a simulator, but has a pretty good schematic capture.

I use this as well, and although it's a little clumsy to use, you get used to it. I like the simulator, but I did find it strange that I put in a circuit for an isolated SM power supply, and it didn't like the isolation, making me earth the input (which is naughty in SM power supplier).

What's a good program for laying out PCBs? I used to use ezy tracks years ago, but haven't made one for many years.

 

[Roff]

I use this as well, and although it's a little clumsy to use, you get used to it. I like the simulator, but I did find it strange that I put in a circuit for an isolated SM power supply, and it didn't like the isolation, making me earth the input (which is naughty in SM power supplier).

You can generally earth a floating input through a huge resistor, such as 1e12 ohms (1 million megohms).

What's a good program for laying out PCBs? I used to use ezy tracks years ago, but haven't made one for many years.

 

[joelumuna]

the meaning of electrode

electrodes is any material that allows electron to flow

 

[Ussama]

It is really gr8......by tha way nice idea 4 tha next science fair....thnx

 

[diablo1]

whats a 5K pot mean?? I know what a resistor is but whats a pot? The difference? Also do you need two 4.5V battery sources? What are those in the schematics?

 

[Roff]

whats a 5K pot mean?? I know what a resistor is but whats a pot? The difference? Also do you need two 4.5V battery sources? What are those in the schematics?

A pot (short for potentiometer) is a resistor with a 3rd terminal (wiper) that is a variable tap. If you connect the wiper to one end of the resistor, you have a variable resistor, also known as a rheostat.
I posted an equivalent version of the original circuit that only uses one 9V battery on page 2 of this thread. I've attached it below.
You can use almost any general purpose NPN, such as 2N3904, etc.