The circuit is an extremely simple ohm-meter.

__________________
Uncle $crooge

 

So, If I'm a really sweaty gross kind of person. I'm a really bad lair.

I think someone really has it out for stinky sweaty people.


kv

__________________
Truthiness Monkeys : Obedience, Ignorance, Fear.

 

If you're a short circuit before the questioning starts, that's the baseline. You can lie like a rug and no one can tell.

__________________
Ron

 

This is based on the fact that when people lie they presumably sweat a bit because they are stressed. So many co-factors could explain the jumping of the multimeter, e.g. the lights in the room are too hot making the hand sweet or that theyr scared your going to shock them with your scary looking lie detector

Build this if your bored

Mike

 

No, you build it for stinky sweaty people.

The when they lie during the interview you shock them for wasting your time.



kv

__________________
Truthiness Monkeys : Obedience, Ignorance, Fear.

 

sir,
why don't i get the selected thing.i am a student of 15years .give me simple low cost electronic project.

 

You can get ECG electrodes from a hospital that stick on your skin to create a more-reliable connection. You can then measure the internal resistance of your body.
Most of the resistance of your body is in the small distance between the outside of your skin and the inside of the skin.
If you press harder on an electrode, the resistance decreases enormously.
This effect is much larger than the change in resistance due to sweating.
That's why lie detectors are so inaccurate.
I have a circuit for a "super-sensitive" lie detector for those with dry skin.
A person with dry skin does not activate a simple lie detector AT ALL.

 

Actually lie detectors are inaccurate because a knowledgeable tester can manipulate the subject and a knowledgeable subject can manipulate the test. Last time I checked lie detector tests were inadmissible as evidence in US court because the test is so easily manipulated.

__________________

 

And even at best the interpretation of test results are very subjective.

I recall some decades ago the show 60 mins did a report/expose on lie detectors and the agencies that contract out their services. It was a setup where they pretended to be a small company that was having some office thefts and that while they suspected a specific employee who they did identify to the testers, they had no proof so wished to have all the office employees tested. The results from three different agencies were all the same and that was that the suspected employee was lying and only he was lying. Of course the suspected employee was an actor (as were all the 'employees') and was told not to lie. Funny that results equaled expectations! Of course all three agencies denied subjectivity (or worst, fraud) and said the tests were flawed because all the actors were not under real life stress. Also turns out that the lie detector association is a very profitable organization that 'sells' certifications for their 'member' agencies and help keep out independent and 'non licenced' and 'unqualified' testers.

As practiced, at least in that N.Y. city area, it is or was at least then a scam and just a way for some people to make a rather sleazy living.

Lefty

__________________
Measurement changes behavior

 

Hopefully the trend is nearly spent =) I remembered from my 5 in 1 sheet from work.
Employee Polygraph Protection Act

__________________

 

Interesting read. Did you notice all the exemptions from this law, nearly all government and military are not restricted in anyway from using polygraph testing.

Always strange how a goverment for and by the people can often pass laws that apply to normal people but exempt themselves.

Lefty

__________________
Measurement changes behavior

 

And for the person looking for the M1 mA reader to make the schematic in pPsice... Just draw a short circuit and put your current probes on that node and have it output that to a graph. I'd take a digital multi meter and measure your skin, and use that as a load across where the electrodes would go. Then graph that current. Then you could increase and decrease the load resistance a little be and see how this effects the current. i.e. you would be modeling it after how a person's skin resistance could increase or decrease and the effect it would have on the current that you are motoring.

 

Hey guys I have a question was hoping could be answered. I'm an EE undergraduate student so I have been exposed to many type of transistor circuits.

Can you tell me what role the capacitor plays in this circuit? I do not understand why there needs to be a capacitor connected in between the two electrodes.

Thanks

 

The cap is probably not necessary. Human bodies will generally have a lot of common-mode mains-related voltage (primarily 50 or 60Hz, depending on where you live), but this is relative to earth ground. I don't think there will be enough differential-mode noise to drive the transistor into saturation on the peaks, which would screw up the bridge. The cap is probably cheap insurance though, just in case.

__________________
Ron

 

can any one explain how it will work?