Amplifying EMG sensor signal ?

Using Arduino Sensors
1

Hi,

We bought the following EMG sensor: http://www.seeedstudio.com/wiki/Grove_-_EMG_Detector
When no muscle contraction, we obtained a 1.46±0.02V output.
When maximal contraction, the signal change to 1.51 with some peaks at 1.55.
Typically, an EMG output goes from few mV to 30mV...

We think we need to amplify the analog signal. We are sport science students taking the challenge to "hack" an EMG for a laboratory class. As you can imagine it is very challenging...

We did some research and considered the following option:
deviate the signal wire to a series of two amplifiers before plugging to the analog pin. Here are the characteristics:
-9/+9 power supply
amplification*15: TL072 with two resistors (150KOhm and 10KOhm)
rectification (-) -> (+): TL072 with two resistors (both 10KOhm)

Does it look OK?
Is there any easier option? (we frequently saw recommendations for rail-to-rail opAmp during our search on internet, but we cannot understand how it works)
Is there any module/boardbreak doing this simple amp job for Arduino analog input?
Any suggestion (especially product name)?

At this stage, our objective is to demonstrate the EMG changes during (for example) a ramp muscle exercise. We do not plan to add any smoother/filter at the hardware level. we just want to show to our teacher the EMG changes using a serial plotting software.

THank you for your help !

Juri

2

We think we need to amplify the analog signal.

From the schematic diagram, that board already has a high quality instrumentation amplifier, followed by another gain amplifier. You won't be able to improve on that design.

I suspect that you not using the board correctly. The product page claims that you should see easily measurable signals of 1 or more volts upon muscle contraction.

3

Dear Jremington,
Thanks for your answer.

I was also thinking to get this kind of ready to use OpAmp breakout (SparkFun OpAmp Breakout - LMV358 - BOB-09816 - SparkFun Electronics), but yes in the meantime of your answer, I noticed on the schematic that already two amplifications "modules" are included on the board.

I think I am using the board in the right way. I am used to work with EMG/ECG and would not suspect any problem here. There is this grove-specific connection system that I got rid of... because I am not using a grove base shield. So I cut the wire and plug them directly in the Arduino board Pin.

Just to confirm, you think a rail-to-rail OpAmp chip cannot help much here?
Again, I can see some magnitude changes when I contract my muscle (max contraction only) but only few (5-10) mV.

Thanks for helping !

Juri

4

Just to confirm, you think a rail-to-rail OpAmp chip cannot help much here?

No. You are simply wasting your time.