Hi Ram,
1. Can you verify that you are contracting the muscle during the period that you expect to see the signal? If you have doubts as to whether your EMG sensor is functioning correctly we suggest that you first use a signal generator to determine if you can capture a standard waveform signal. Also lead-off can be tested—signal should head towards max/min in an obvious pattern. 2. The Shimmer GSR measures skin resistance (or inversed, skin conductance). GSR is a complex signal which requires a proper understanding if it is to be used correctly however the basic operation of your GSR sensor can be tested using a variable resistor as a substitute for the human skin. 3. Perhaps the difference is due to motion artefact? Are you seeing the difference when you move the area of interest or simply when the accelerometer is enabled/disabled? Also, to deal with Shimmer Research directly you should contact us through [email protected], as we can respond more efficiently through the support channel. Best Regards, Karol From: [email protected] [mailto:[email protected]] On Behalf Of Ramanathan Subramanian Sent: 16 January 2012 09:15 To: "[email protected]" Subject: [Shimmer-users] Shimmer EMG, GSR manuals for dummies Hi all, We are trying to use the Shimmer EMG, ECG and GSR sensors for affective computing experiments, but are having some problems. I am listing them as follows. We are unable to find demo videos (except for ECG), to check if our method/expected output is right. Also, there is no specific information regarding these sensors in the Shimmer manual. Can somebody please help? 1. To start with, there seems to be no output from the EMG sensor!. There are some exemplar images shown at <http://www.shimmer-research.com/p/products/development-kits/emg-development -kit> http://www.shimmer-research.com/p/products/development-kits/emg-development- kit showing the EMG electrodes, but we heard from Karol that these images are for illustration purposes only, and the electrode placement may not be scientifically correct. We also checked out a few Youtube demos, which say that the reference electrode should be placed on a bony part, with the positive and negative placed on a muscle, so that the potential difference is amplified by the EMG sensor. Accordingly, we tried two configurations as in the images below (the middle and right images in 'çonfiguration.jpg' correspond to the 2nd configuration) , but there seems to be no significant difference in the EMG output as shown in the waveform. We checked the sensor offset, which is very close to the default value, though we we unable to verify the gain. However, it is very strange that there appears to be NO OUTPUT... 2. With GSR, we got some response, but are unable to verify whether the output is correct. Is the GSR response supposed to peak when the person is aroused (stressed)? (if the GSR is a measure of the skin conductance, this is the expected response as per Wiki). 3. Finally, each platform comes with an accelerometer. We tried to record the accelerometer output along with the ECG output, but then the ECG output was different when the accelerometer was enabled/disabled. So, is it reliable to record data from both sensors at the same time? Overall, it would be great to know if there are simple tests to verify if the EMG and GSR sensors are working correctly are not..we need to start with pilot experiments soon, and would be grateful if somebody can help asap! Thanks Ram Error! Filename not specified. Error! Filename not specified.
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