EMG Cable Interference

Cables, Electrodes, Plugs, etc.
BITalino
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EMG Cable Interference

Postby BITalino » Wed May 20, 2015 10:51 pm

Hi there,

Reports have arrived of cable interference when using EMG sensors. From our experience so far we've managed to use the EMG + 3-lead accessory arrangement even in dynamic conditions apparently with little or no motion interference, as shown here:
https://www.youtube.com/watch?v=co_f_aaHEEA
https://www.youtube.com/watch?v=pVAaFeym8TQ

Nevertheless, here are a few possible causes and fixes in order to overcome potential problems you may be experiencing:

1) For the sake of providing BITalino at the lowest possible cost, we provide it as a bare PCB, which means that it will be more prone to electromagnetic noise; please refer to the following thread on our forum for some useful tips on how to go about this: http://forum.bitalino.com/viewtopic.php?t=236#p614

2) A noteworthy aspect is the ground lead (the middle cable on the 3-lead accessory); good practices recommend you place it in a bone area (electrically neutral), such as the elbow, C6 cervical, etc... of course you're free to use any alternative configuration that you’d like (and it will work fine for most typical applications), however, you may see slight baseline wanders (which are not present in the “by-the-book” configuration) especially when the muscle is contracted.

3) You can try to wrap your electrode cable into a loop (see attached photo), which should act like a makeshift shielding of sorts.

4) The electrode cables are not shielded, reason for which when touched by a person other than the user to which the sensor is connected, this person may be inducing an electric field given that his/her body is at a different potential than the BITalino + connected user arrangement.

5) You can try to get rid of the 3-pin Molex Sherlock plugs and solder the electrode cables directly to the board… this would solve it if the problem is in the Crimp Pin / Molex Sherlock interface.

6) Cut the + & - electrode cables to a smaller length (e.g. 2cm) and have the sensor as close as possible to the placement point (just take care to have some insulation layer between the sensor and the skin to avoid artefacts potentially arising from the sensor/skin contact); an example of such a configuration is shown in the attached photo (there are others).

Best regards,
The BITalino Team
Attachments
IMG_5650.JPG
EMG Sensor Assembly
IMG_5650.JPG (43.28 KiB) Viewed 1890 times
3lead_cable.jpg
3-Lead Accessory
3lead_cable.jpg (27.16 KiB) Viewed 1890 times

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