I have purchased three MyoWare 2.0 Muscle Sensors in this April and am trying to get an EMG signals on a microcontroller board. The sensor output stays constant around 3.0V whether I apply force or not. They do not seem to be working properly, so need help.
Setup Description
- A MyoWare 2.0 Muscle Sensor (v2.0.4) is attached to my bicep and connected to an STM32H747I Discovery board with a 3.5mm audio cable via a Link Shield attached to the sensor (See the attached "how_to_connect_sensor.jpg").
- A MyoWare 2.0 Arduino Shield is attached to the board and a 3.5mm audio cable from the MyoWare v2.0 sensor is connected to A0 port on the shield board.
- The board is powered via the USB port of a laptop without an AC adapter connection.
- The sensor signals are captured at A0 pin by Analog Discovery 2 (a USB oscilloscope) and can be seen as a chart (See the attached "how_to_probe1.jpg").
Results
The attached video (“MyoWare2.0_Switch_On_3.gif”) shows what the voltages on A0 pin varies like from the sensor being turned on (00:05) to turned off (00:25). As you can see, the value stays around 3.0V during that period of time; no change is seen in signals, even if the bicep is relaxed or flexed. The same waveforms are obtained even if we use the other two sensors instead.
Please advise me what to do to get the EMG with MyoWare 2.0 Muscle Sensor.
Many thanks in advance.
Try adjusting the gain pot https://learn.sparkfun.com/tutorials/ge … cle-sensor (scroll down a bit) - does it alter the output?
BTW the sensor should be on the muscle belly instead of to the side https://learn.sparkfun.com/tutorials/ge … are-hookup, closer to the midline…though that wouldn’t account for the 100% signal being seen in the video :-/
What is the IO voltage of the MCU being used ?
Try adjusting the gain pot https://learn.sparkfun.com/tutorials/ge … cle-sensor (scroll down a bit) - does it alter the output?
OK, I'll try it & post the results later.
BTW the sensor should be on the muscle belly instead of to the side https://learn.sparkfun.com/tutorials/ge … are-hookup, closer to the midline…though that wouldn’t account for the 100% signal being seen in the video :-/
OK, I'll attach it on the muscle belly next time.
Are you saying that the strength of the myopotential changes depending on whether it is the belly or the sides?
What is the IO voltage of the MCU being used ?
I'm using 3.3V as the IO voltage.
Yep, generally the action potential propagates down the midline (shortest path) of whichever muscle mass is contracting
Measurements were taken after adjusting the gain to settles the valeus within the range of 0 to 3.3V. As shown in the attached figure, the gain fluctuates finely whether it is relaxed or flexed.
It seems that the EMG potentials are not sensed.
Is there anything else for confirming?
All three sensors behave the same, but is it possible that they are all broken?
I’d say try noting these:
For your convenience, the following troubleshooting tips 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.
What’s the ENV LED look like?
If the problem persists it might be defective
I’d say try noting these:
For your convenience, the following troubleshooting tips are provided from the MyoWare 2.0 Quick Start Guide.
Thanks, but I've already read them.
And , as you picked up, it says as follows:
Most of the time the sensor gain does not need to be adjusted at all.
I adjusted the potentiometer to keep values within 3.3V, but isn’t that necessary?
What’s the ENV LED look like?
I think the ENV LED is designed to turn on and off depending on the output potential. And it is working as it should.
If the problem persists it might be defective
I would like to return them if they are defective, but please let me know where I can start the procedure.
One question.
If you think a sensor is not working properly, what steps do SparkFun’s engineers take to investigate? I would like to know as far as you could share.
Head over www.sparkfun.com/returns if purchased from us, or contact vendor for similar if purchased elsewhere to request either a replacement or a refund