EMF Ecologies is a series of experiments in capacitance sensor design, DIY printed circuit board fabrication, and reactive systems. EMF Ecologies was developed in collaboration with Cayden Mak for the course Media Robotics I: Physical Computing offered by the Department of Media Study at University at Buffalo.
Capacitance sensing has its roots in the polygraph, producing fluctuations on paper which at the same time are responsive yet unpredictable. Our project started out as a polygraph of sorts: a necklace which measured GSR (galvanic skin response) and displayed the fluctuations with an LED array. We noticed, however that our device reacted to our bodies even without wearing it. This effect is due to the changes in static electricity clinging to our bodies: capacitance.
We were using Arduino for the GSR necklace, but I was convinced that the capacitance effect had nothing to do with the code we wrote (which measured resistance), and should be able to be reproduced using analog components only. At the time I had a limited knowledge of analog electronics, but I understood that I would need some way of taking single input (antenna) and using it to control the flow of electricity to an LED. This meant I needed to use a transistor. A single transistor was not sensitive enough to amplify the faint tug of the electrons on our bodies, but several transistors can be wired together, each amplifying the output of the previous. By experimenting with the number of transistors, I found that four was the right balance of reactivity and sensitivity.
With our simple circuit, four PNP transistors, one LED, one resistor, a wire as an antenna, and a battery, we constructed our sensors sans circuit board. The tiny structures resembled little bugs, and we began to think of them as having unique personalities, for their behavior was never the same. Here is a more complete write up of this stage of the project.
I found that I was able to consistently get the bugs to react to me lifting my shoe off of the ground. There is obviously quite a charge between the soles of our shoes and a tiled floor. I could then wave my hand over the antennae to direct their attention. Here is a short video showing just how responsive these circuits are:
For the last stage of this project we wanted more. The bug form was a nice personalized object, but we wanted to see what it was like to have a lot of these lights embedded in a space. In order to do this we would need mass production--on a small scale. We decided to print our own circuit boards to make construction easier as well as making the final project more durable. A video of our first attempt at circuit board fabrication can be found here, and a more complete write-up of this stage of the project, along with a how-to can be found here.