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Lie detector...

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bogdanfirst

New Member
a few days ago i ha an idea, to build a lie detector.....using the computer...
so i made some electrods and i conected them in place of one of the potentiometers of the joystick.....and placed a 1M resstor in paraledl vith them.....and tested it on someone, and the graphic worked quite well, u can see different variations when sb answers the questions, it's all to reading th graph......
but i works different to diferent persons because the skin's electrical resistance is different, so i must adjust the resistance in paralel with the electrods, wich in some cases is not necesarry.....
i also build a smal program in pascal, and myabe if ill have tim ill build something in c....
so anyway if u think someone is lying, try this!! :D
 

McGuinn

New Member
mark,
Any chance you could decrease the size of your sig as at 155KB it's a bit much for the slower 56k modem owners to download.

bogdanfirst,
Maybe you need to place a line or two in your code which will take an average resistance first and readjust the base line resistance... Is it your own code?
 

bogdanfirst

New Member
yep, it is my own code. it is in pascal, it is very rudimentary,
the reslution is 480 x 640 and the resistance that the computer mesures is from 0 to 470K with a precision of 1K. so i just put a pixel at the (Y1, X) coordonate of the read value, and then the next pixel at (Y2, X+1) and then i unite them with a line. the graph looks quite nice.
but it would be nicer if i could have a ADC and read the values from the serial or parlalel port.....wouldnt it?
 

McGuinn

New Member
I hadn't read about the joystick port in quite a long time and forgot about it's limits as you mentioned.
My only other idea would be to incorporate a rotary switch with increasing resistor values which could be used similar to a range selector on a multimeter...
 

stevez

Active Member
Please do not take this as an insult - be careful that you don't expose yourself to lethal electrical currents. I was "playing" with measuring my heart rate once using an oscilliscope and some other gear. It worked well but I stopped after having a chilling thought that none of the equipment I was using could be considered safe for that purpose. None of the instruments would create a problem if working correctly but there were a zillion failure modes that could have turned my fun into disaster. That's why medical equipment is so carefully designed.

Just sharing a lesson.
 

bogdanfirst

New Member
i dont take that as an insult. and i apreciate the advice. i always try to buils safe devices. but since there are only 5V on the joystick port, i dont think that this could be a problem. also i mesured the resistance only at one hand. so if a shock was to be produced the current wouldnt go trough the heart. also, how did you mesure your heart beat? i think you need an electrode on each hand or one electrode to the left hand and one to the right leg.....
i know that when i tested the detector on me, i was getting my heart beat graphic, along with the resistance one.....i feel like an alien.. :lol:
 

astralbrook

New Member
need help

how do we link our lie detector circuit to PC?
through RS232, serial port, parallel port or midi port at sound card?
do u have any software will monitoring the input of the signal?
mind to share urs idea or works with me?

thanks.
:wink:
 
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