The Polygraph Machine

A few months ago I was rummaging though a box and found some electronics components.  To immediately digress I can never throw such things away, and when old electronics are being tossed, I'm there with a soldering iron to rescue parts.  Anyhow, I had found a small amplification chip, a headphone jack and some DIY PCB.  A long time ago, the specifications for the OLPC XO-1 laptop had a curious feature, they were going to use the microphone in port as something other than just a microphone, Geiger counters, conductivity checkers, and a whole slew of things that wouldn't have needed a driver that were just basic I/O systems.


A very simple polygraph just registers the resistance of skin (you can see where I'm going now, can't you?)  By itself the microphone port wouldn't have had enough power to check conductivity, but if you used a battery and an amplifier, well, that is another story.

Around midnight, after drawing a quick schematic (and I'm sure an improper one), and having a poison scare dealing with Ferric Chloride (accidental ingestion), I came up with this:

The Polygraph

To finish off here, I installed Audacity hoping that it would work rather than building some PyGame/Matplotlib/Python monstrosity for a simple test of the equipment.  Some scary sounds came in when I placed my fingers on the terminal.  Attached here is the first sample I took, some features to note:

• High buzzing sound
• Second 27?
• Seconds 21-24, Cannon in D?