Tuesday 1 December 2015

Experimenting with EMG

In the upcoming issue of 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 [1]. 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 
The eagle CAD file is available for download
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 [2] or an EMG shield for Arduino [3]. If you look more for commercial device you will find in [4] a good overview and also an introduction to emotion sensing.

[1] 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.
[2] http://www.openbci.com/
[3] https://www.olimex.com/Products/Duino/Shields/SHIELD-EKG-EMG/ 
[4] Kanjo, Eiman, and Alan Chamberlain. "Emotions in context: examining pervasive affective sensing systems, applications, and analyses." Personal and Ubiquitous Computing: 1-16