TRUE / FALSE
Do-It-Yourself Polygraph Workshop
Infas, the German institute for applied social science, recently celebrated its 60th anniversary with a little festival. Kati and I were invited to give a workshop as part of the event. We thought that it would be funny to build polygraphs (i.e. "lie detectors") together with the party guests, as infas is basically looking into people's heads in order to find out what they think.
On top of that, the concept of the workshop humurously touched issues like "truth" and "fake", which are relevant in today's social media driven world, as well as the quantified self movement, because polygraphs and fitness trackers are technically quite similar devices.
Historic background
The history of lie detectors is quite fascinating. It started 1906 with James Mackenzie's invention of a mechanical device, which could continuously measure a person's heartbeat and record it by drawing it as a curve on a roll of paper.
Physiologist and police officer John A. Larson developed the device further, added a feature that would also record breathing and called it "cardio-pneumo psychogram". He started using it during the interrogation of suspects from 1921 on. The machine became quite popular and the press gave it the catchy name "lie detector". However, Larson's device could not detect any lies, but only record some bodily functions. "Detecting lies" was done by interpreting the recorded curves by the operating investigator. The underlying assumption was that suspects would become more nervous when lying, which could be visualized with the polygraph.
Larson's initial goal was quite noble: Rather than using plain violence in order to make suspects confess a crime, he wanted to offer police officers a more scientific method for the interrogation. At the end of his life, Larson was not very happy with his invention, though. He regarded his development of the polygraph as a massive waste of time.
Our selfmade polygraph
For the workshop, we developed a little device that can be made in a relatively short time, by people who have no prior experience with building electronics. We used only parts which are easy to source. The outcome was a simple polygraph, which can measure a person's pulse and variations in skin resistance. A little display shows the data as two curves, much like an oscilloscope.
Our device was built around an Arduino Uno, which we have chosen because it is relatively well known, even beyond hacker/maker/diy circles. All components were connected via a solderless breadboard and jumper wires. The pulse sensor was an off-the-shelf module, which works optically. The sensor for measuring the skin resistance was selfmade. It's a voltage divider where one resistor is the skin, and the other one is a 5.6 МΩ resistor. A little TFT module served as display and the whole device was powered by a small power bank.
It was a bit challenging to connect the display, as the voltage levels of the Arduino and the tiny screen didn't match. Getting it running required a bunch of voltage dividers. Therefore, we also prepared some example setups on breadboards, making it easy for the participants to replicate.
We put the parts as a kit in little cardboard boxes. The kit also included a photocopied zine-style handout with instructions, schematics and a list of materials. The box was reused later as a case for the finished device. We brought a lot of funny and interesting materials with us, from googly eyes to glitter foil, with which the participants could decorate their polygraphs individually.
Finished polygraphs
The final devices turned out quite nice in my opinion. So I'll leave you with some impressions of the participants and their creations. In case you want to build something similar, please scroll to the very end of this post. There you can find links to some resources, which will help you making your own polygraph.
Workshop resources
- Workshop handout (German version)
- Arduino Source Code
- Photo album