Arduino + PluxEMG does not output any Signals

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jhennrich
Posts: 4
Joined: Wed Aug 17, 2016 1:53 pm

Arduino + PluxEMG does not output any Signals

Postby jhennrich » Mon Aug 22, 2016 3:33 pm

I am trying to measure EMG Signals with an Arduino Uno for my Masters Thesis. I found this wiring example and tried to reproduce it. I am using an old Plux emg sensor and I expected it to work similar to the Bitalino sensors, but I dont get a signal at all.

Apparently someone ripped off the plug of the eng sensor, so I compared the wires colors to a functioning sensor. I believe the correct wiring pattern is:
red = VCC
white = VOUT
black = VSS
shielding = GND
green = unused

I connected the emg sensor to the Arduino in the following way:
schaltplan_arduino_plux.png
schaltplan_arduino_plux.png (25.49 KiB) Viewed 2409 times

with R1=R2=10kOhm

The output I get at A0 is a constant value around 152 (+/- 1), which is around 152/1034*5V = 0.74V.

I power the Arduino via USB from a Notebook that is not plugged in to AC.

I think the possible reasons why this fails are:
- my color pattern for the emg sensor is wrong
- my emg sensor is broken (since someone ripped off the plug this isnt very unlikely, is there a simple way to test it?)
- my circuit is somehow wrong, but i doubt Plux sensors need a different circuit than Bitalinos.

Cheers,
Johannes
Master's Student - Computer Science - Karlsruhe Institute of Technology

maert
Posts: 1
Joined: Fri Feb 19, 2016 10:55 am

Re: Arduino + PluxEMG does not output any Signals

Postby maert » Tue Aug 23, 2016 12:56 pm

Did you connect only one sensor to Arduino? I had similar problem. In my case the 10kOhm resistors were too much, used 2 x 4.7k instead. Also, i recommend to replace on of the resistors with trimpot for offset correction.

BITalino
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Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Arduino + PluxEMG does not output any Signals

Postby BITalino » Tue Aug 23, 2016 1:01 pm

Hi Johannes,

Considering that by old PLUX EMG sensor you mean the version in the photo bellow, the input voltage may need to be 5V:
https://www.physiosupplies.eu/media/cat ... olo-39.jpg

RED will definitely be your VCC, the SHIELDING will be your GND (0V) VSS, the BLACK wire should be the GND (0V) and the WHITE wire should indeed be the signal. If the 5V supply doesn't do it, the other thing you may want to try is using the green as the VSS.

Let us know in case you continue to experience any issues with making the sensor work and we'll try to provide additional information.

Note that even if you get the sensor up and running, the fact that it is powered from the USB of a computer, which in turn is connected to a power source, may lead to an extremely poor signal-to-noise ratio.

Best regards,
The BITalino Team

jhennrich
Posts: 4
Joined: Wed Aug 17, 2016 1:53 pm

Re: Arduino + PluxEMG does not output any Signals

Postby jhennrich » Mon Sep 05, 2016 3:33 pm

Thank you for your replies.

I tested again using a different sensor, but the results are the same. So the problem should not be a broken sensor.
Also I tried different resistors between 3.3kOhm and 10kOhm for the voltage divider, the results were all the same.

But now i noticed that the voltage level at VSS drops when I plug in the sensor. With VCC=3.3V the VSS is at 1.65V without sensor connected and when I connect the sensor it drops to 0.79V. The same happens when I power the sensor with VCC=5V, with the sensor connected VSS drops from 2.51V to 0.81V. The Voltages at VCC are stable though.
In my understanding it is very logical that VSS drops when I connect something to it, but I am not sure if It should drop by that magnitude. Can anyone explain if this behaviour is correct?

This is my setup:
arduino_sensor_emg_1.jpg
arduino_sensor_emg_1.jpg (196.38 KiB) Viewed 2350 times


Best regards
Johannes
Master's Student - Computer Science - Karlsruhe Institute of Technology

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Arduino + PluxEMG does not output any Signals

Postby BITalino » Mon Sep 05, 2016 4:03 pm

Hi Johannes,

It looks like your VSS line currently coming out of the female plug should be connected to the GND and your GND line should be connected to the VSS instead.

Provided that the resistors have the same value, the 3.3kOhm should be good enough to provide for the midpoint voltage. Please confirm whether switching the VSS with the GND solves the issue and let us know how it goes.

Best regards,
The BITalino Team

jhennrich
Posts: 4
Joined: Wed Aug 17, 2016 1:53 pm

Re: Arduino + PluxEMG does not output any Signals

Postby jhennrich » Mon Sep 05, 2016 5:05 pm

The perspective of that photo is indeed not very good, but I believe my wiring is correct:

arduino_sensor_emg_vp.jpg
arduino_sensor_emg_vp.jpg (113.57 KiB) Viewed 2346 times


The shielding of the sensor wire is connected to Arduinos GND and the black wire is connected to the voltage divider.
Master's Student - Computer Science - Karlsruhe Institute of Technology

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Arduino + PluxEMG does not output any Signals

Postby BITalino » Mon Sep 05, 2016 5:16 pm

Yes, but that's the thing... in our previous post we made a mistake describing the pinout.

The shielding is in fact the VSS and the black wire the GND.

Apologies for the inconvenience. We'll edit the information above in a moment.

Best regards,
Hugo Silva

jhennrich
Posts: 4
Joined: Wed Aug 17, 2016 1:53 pm

Re: Arduino + PluxEMG does not output any Signals

Postby jhennrich » Fri Sep 09, 2016 11:11 pm

Very cool, now this is working like a charm!
Thanks for the help, very appreciated.

Cheers,
Johannes
Master's Student - Computer Science - Karlsruhe Institute of Technology

BITalino
Site Admin
Posts: 567
Joined: Tue Aug 27, 2013 3:47 pm

Re: Arduino + PluxEMG does not output any Signals

Postby BITalino » Sat Sep 10, 2016 7:52 am

Great to hear that everything is working ;)

If you have further questions, just let us know.

Best regards,
The BITalino Team


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