ACM interactions magazine I will talk in my column on interaction technology about the electrical interfaces to humans. This blogpost is written to give you a preview of the article and describes a little project I did over the weekend to explore Electromyography (EMG).
It is the simplest circuit I could find and it results in a very simple and easy to make EMG. It takes less than half an hour to build and plugs into the microphone input of a computer. It uses a single operation amplifier (INA128p) and is based on the description in . Builing the filter into the gain branch is quite nice ;-)
For my Experiment I used the following components:
- a INA128p (Precision, Low Power Instrumentation Amplifiers)
- 2 Capacitors (100uF, Elco)
- a Resistor of 120 Ohm
- 3 copper pieces (e.g. 5 cent coins) as electrodes for the body
- a 3.5mm audio connector (from broken headphones)
- some cables and prototyping board
Connecting it to other parts of the body made a very simple ECG – more suitable to get the heard rate that the shape of the signal.
More sophisticated circuits are available, e.g. openBCI  or an EMG shield for Arduino . If you look more for commercial device you will find in  a good overview and also an introduction to emotion sensing.
 Bhaskar, A, Tharion, E., and Devasahayam, S.R. Computer-based inexpensive surface electromyography recording for a student laboratory. Advances in Physiology Education 31, 2 (2007), 242–243.
 Kanjo, Eiman, and Alan Chamberlain. "Emotions in context: examining pervasive affective sensing systems, applications, and analyses." Personal and Ubiquitous Computing: 1-16