Post by thread:[EE:] Polygraphs

Does anybody know where to find a schematic for a polygraph? Google turned up a few very simple circuits based on changing skin resistance due to sweating, but I'm more interested in how "real" ones work in detecting stresses. Thanks in advance -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

I don't know what specific sensors are used for polygraphs but they'll be part of the biofeedback doctrine. Google for something like biofeedback polygraph biofeedback circuit I did make, a long long time ago, a biofeedback system for a Commodore 64, worked very well. Included a GSR (galvanic skin response) sensor, electromyogram, temperature sensor, heart rate monitor and breathing rate/depth sensor. The electromyogram is probably the most complex circuit, but still used IIRC an LM3900 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

The normal items recorded are breathing depth (a sensor around the chest), skin resistance, muscular activity, and heartbeat. These items by themselves don't mean much. The skill of the operator in developing the questions and interpreting the results is the key to a "good test". Any knowledgeable person who understands how polygraph interrogations work can easily fool the operator and the recorder and will "pass". While used frequently, polygraph examinations are actually nothing more than staged interrogations. The fact that the results are NOT allowed in any legal court shows its true value. And polygraph examinations are rarely made outside the US, as the technique is not considered to be worth the effort. The KGB taught their spies in our CIA how to pass their routine polygraph tests. In years past, witches were strapped to a dunking plank and repeatedly held underwater, as a test of their "witchcraft". If the person died of drowning, she was NOT a witch. Worked flawlessly... sorta like the polygraph. --Bob Robert B. wrote: {Quote hidden}> Does anybody know where to find a schematic for a polygraph? Google turned > up a few very simple circuits based on changing skin resistance due to > sweating, but I'm more interested in how "real" ones work in detecting > stresses. > > Thanks in advance > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- Replier: Most attachments rejected -------------- Bob Axtell PIC Hardware & Firmware Dev http://beam.to/baxtell 1-520-219-2363 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> In years past, witches were strapped to a dunking plank and repeatedly > held underwater, as a test of their "witchcraft". If the person died of > drowning, she was NOT a witch. Worked flawlessly... sorta like the > polygraph. > > --Bob So, if the interogatee weighed the same as a duck ........ ? There's a story big in the news down this way, made world headlines in 1980 http://theage.com.au/articles/2004/07/07/1089000223561.html Despite the extreme and widespread scepticism about Mr Cole's story, he did pass a lie detector test (I heard it was an all-day affair) It could be that Mr Cole actually believes what he saying is the truth (many theories about what could have happened at the time and Mr Cole could even be supressing his own guilt), even if it isn't. Or that he is very wily and can control his body to the extent that the detector passes him. Or could be biased spin put on the result by the news- paper. Whatever, the test didn't provide any clarification, just added to the intrigue -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

How about a new design made from the PIC10F that you put into a capsule and have they guy swallow it. Maybe you could measure that queasy feeling people get in their stomachs when they lie. > > Robert B. wrote: > > Does anybody know where to find a schematic for a polygraph? > Google turned > > up a few very simple circuits based on changing skin > resistance due to > > sweating, but I'm more interested in how "real" ones work in > detecting > > stresses. > > > > Thanks in advance > > --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.699 / Virus Database: 456 - Release Date: 6/4/2004 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email spam_OUTlistservTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body

Hi Lindy: I believe the "real ones" also use galvanic skin resistance, but also pulse rate. Some of the newer devices include voice algorithms which detect critical vocal patterns that appear when one is prevaricating. Most of the analysis in the newer devices utilize Hi-res A/D conversion and run all of the algorithms digitally, unlike the older analog models. I can't point you to a specific site but there is a lot of info if you search on lie detection or polygraph tests. The trouble with polygraph is that there are many polygraph tests that are not related to lie detection. Good luck searching. {Original Message removed}