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 Post subject: Inconsistent EMG sensor readings
PostPosted: Fri Mar 13, 2015 11:21 pm 

Joined: Fri Mar 13, 2015 9:50 pm
Posts: 2
Hello,

I was wondering if someone could help me troubleshoot the EMG sensor on my ehealth shield. I have been using the ehealth EMG to try and read in signals from the forearm. I have connected the lines correctly (I have double checked 20 times) and the jumper is in the correct position. However, I cannot seem to get a reliable signal. Many times when I connect it to my arm, I get very high values (around 800) that do not respond to flexing. On a few occasions I have gotten very good values that range from 11-50 (11 relaxed, 50 fully flexed). Most times though, the number will float randomly between 10 and 500. Is there something that I am missing? Nobody else seems to have had trouble with this. I bought two shields and both are having this issue, so I do not think the problem is with the board. Could anyone give me any advice?

Let me know if I can answer any questions.

Thank you so much,
eDog


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Mon Mar 16, 2015 8:48 am 

Joined: Mon Sep 28, 2009 12:06 pm
Posts: 11292
Hello edog,

Could you post some photos? We will check the hardware connection.

Regards.


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Tue Apr 14, 2015 10:29 am 

Joined: Tue Apr 14, 2015 10:01 am
Posts: 10
Hi.. I have exactly the same problem now. I am able to see many values in the PC serial window, but those doesnt correspond to any variations in my muscle movements... Please see the connection image attached.. Please help


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Tue Apr 14, 2015 10:37 am 

Joined: Tue Apr 14, 2015 10:01 am
Posts: 10
I am not able to attach the image here


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Wed Apr 15, 2015 7:29 am 

Joined: Mon Sep 28, 2009 12:06 pm
Posts: 11292
You can upload the image in some hosting free website and the use the "image" button in the post menu.

Regards.


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Wed Apr 15, 2015 10:52 am 

Joined: Tue Apr 14, 2015 10:01 am
Posts: 10
Hi
Please see the connection diagram here....

http://postimg.org/image/ljvrc2dqz/
Image

Also see the data received in the Serial Monitor as below
http://postimg.org/image/9whsbwnp9/


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Thu Apr 16, 2015 9:15 am 

Joined: Mon Sep 28, 2009 12:06 pm
Posts: 11292
Please, represent this values in a graph (using excel for example)

The muscle variations are very small. You can use the potentiometer to obtain more gain.

Regards.


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Tue Apr 21, 2015 2:50 pm 

Joined: Tue Apr 14, 2015 10:01 am
Posts: 10
I have saved the data in an excel sheet already. I have also plotted the values at run-time so that I can see the variations properly.. But no use..The data was sent to the PC in every 1mseconds using the function delay(1) so that it meets the sampling requirement for EMG.

The code is as follows

#include <eHealth.h>
#include <eHealthDisplay.h>

// The setup routine runs once when you press reset:
void setup() {
Serial.begin(115200);
}

// The loop routine runs over and over again forever:
int EMG;

void loop() {
//
// unsigned long time = millis();
// //prints time stamp - since program started
// Serial.println(time);

EMG = eHealth.getEMG();
Serial.print(EMG);
Serial.println("");

delay(1); // wait for a millisecond

}

Now I doubt about the ADC conversion by the board.

Is the accelorometer inputs are also given to the same ADC terminals?

Interestingly the Accelerometer looks working fine, since it gave me proper results in the serial terminal.


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Wed Apr 22, 2015 8:27 am 

Joined: Mon Sep 28, 2009 12:06 pm
Posts: 11292
Hello PeaceTsy,

Please try to change this line:

Code:
delay(1);   // wait for a millisecond


to:

Code:
delay(100);


Try and tell us your results.

Regards


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 Post subject: Re: Inconsistent EMG sensor readings
PostPosted: Wed Apr 22, 2015 9:57 am 

Joined: Tue Apr 14, 2015 10:01 am
Posts: 10
I had already tries with delay(100); delay(10); delay(1000); etc..which just changes the frequency of sending the data to the PC.. None of them showed variation based on the EMG inputs...

Additionally, when the EMG electrode pins are read using a multimeter, I could see variations in mVolts, but in PC just some series of values without corresponding changes....


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