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

Sensor modules for acceleration, gyro, and magnetic field

I came across 2 Sensor module recently released by ST Microelectronics:

• LSM303DLH - 3-axis accelerometer and 3-axis magnetometer in a single chip
• L3G4200D - low-power yaw, pitch and roll digital gyroscope

There will be in the future probably very few mobile devices without such sensors. When we worked on the project TEA in 1999 it seemed far away… What can you do with sensors on the mobile? There are a few papers to read: using them for context awareness [1], for interaction [2], [3], and for creating smart devices [4].

Last week in Finland I met Antii Takaluoma (one of the co-authors of [1]) and he works now for offcode.fi - I saw impressive Linux hardware - I expect cool stuff to come :-)

[1] Schmidt, A., Aidoo, K. A., Takaluoma, A., Tuomela, U., Laerhoven, K. V., and Velde, W. V. 1999. Advanced Interaction in Context. In Proceedings of the 1st international Symposium on Handheld and Ubiquitous Computing (Karlsruhe, Germany, September 27 - 29, 1999). H. Gellersen, Ed. Lecture Notes In Computer Science, vol. 1707. Springer-Verlag, London, 89-101.

[2] Hinckley, K., Pierce, J., Sinclair, M., and Horvitz, E. 2000. Sensing techniques for mobile interaction. In Proceedings of the 13th Annual ACM Symposium on User interface Software and Technology (San Diego, California, United States, November 06 - 08, 2000). UIST '00. ACM, New York, NY, 91-100. DOI= http://doi.acm.org/10.1145/354401.354417

[3] Albrecht Schmidt. Implicit human computer interaction through context. Personal and Ubiquitous Computing, 4(2):191-199, June 2000

[4] A. Schmidt and K. Van Laerhoven. How to Build Smart Appliances?, IEEE Personal Communications, p.66 - 71, (2001)