Issues with MyoWare muscle sensor

Other
1

Every time the sensor is turned on, 1 or more of the following problems occur and do so in an unpredictable manner.

All the pictures for our set are in https://photos.app.goo.gl/5yvBaeiVBAtrc94h9

It includes 1 or 2 myoware 2.0 muscle sensors, a usb isolator, SparkFun Redboard, SparkFun Arduino shield and laptop running on battery.

The code to output the readings from the muscle sensor is in the photo album

  1. The env green light is sometimes on (a)when the sensor is not in contact with the muscle or (b) when the sensor is in contact with a muscle at rest. See picture in album

  2. The graph on the serial plotter is sometimes “upside-down”: it starts at the top when the muscle is at rest and it dips when the muscle is flexed - see picture in album

  3. In the “envelope” setting, the peaks of the spikes are squared off/chopped off (no variation in the amplitude of the waves) -

  4. The wave signals do not accurately reflect the flexing vs resting of the muscle (ie., Sometimes a wave signal appears when muscle is at rest, and conversely, sometimes no wave activity is seen when muscle is flexing)

  5. Sensor is extremely sensitive to sound and fast hand movements in the area of the setup even when the sensor is not in contact with skin (graph spikes sometimes when there is noise or talking sound, or fast motions above the sensor) - see figure above

—-- Response

  • What type of cable are you using between the link shield and Arduino shield?

This is the cable that connects link shield to Arduino shield - https://www.amazon.com/dp/B0BQF87G62?ref=ppx_yo2ov_dt_b_fed_asin_title

  • What is your gain set to?

Here are the pictures of the gains on the 3 different sensors that I have. I am not able to tell what the numerical value is. Is it possible to output the gain via code?

Please see pictures of the 3 sensors for the gain values

  • What happens when you turn off the Serial output?

When I turn off the serial output, the ENV light sometimes stays on, sometimes flashes, and sometimes stays off - these 3 behaviors appear to happen randomly as far as I can tell.

  • how are we placing the sensors?

Sensor position is also shows in the photos in the album

2

From our guide:
" For your convenience, the following troubleshooting tips for the MyoWare 2.0 Muscle Sensor are provided from the MyoWare 2.0 Quick Start Guide.

  • The Vin LED should remain on constantly as long as the sensor is powered.
  • The ENV LED might immediately turn on when power is turned on but it should turn off after a second or two; afterwards, it should only turn on when the sensor detects muscle flexion.
  • The ENV LED might sporadically turn on and off or simply remain on if the sensor (or external cables) is not connected to electrodes on the skin. This is normal behavior.
  • The ENV LED lighting up seemingly at random while connected to electrodes on the skin usually indicates poor contact between the electrodes and the skin. Try cleaning the area and applying new electrodes.
  • The ENV LED not lighting up during flexion could be caused by various issues with the sensor setup. Double check the steps and tips of this guide to ensure proper setup.
  • Most of the time the sensor gain does not need to be adjusted at all.
  • Recommended that you do not adjust the sensor’s gain until you get a consistent, quality signal from the sensor."

Your pad placement/alignment is the biggest issue I see…go through this paying special attention to all notes Getting Started with the MyoWare® 2.0 Muscle Sensor Ecosystem - SparkFun Learn

I am also a bit suspicious of that TRRS cable, or hot-swapping being responsible for the inverted values.

Also probably remove the usb isolator while using a laptop (only needed when plugged into a wall/grid source), it ma be introducing noise to the system

3

Thanks for the response. If TRRS cable is suspect do you have an alternate you recommend we should try ? Please advise. We will try the other recommendations per your recommendation.

Ashok