Constructing An Electromyogram (EMG) Circuit

[working_on_EMG]

Hello there. Im a newbie in this forum. Early this year I constructed a circuit to measure EMG from the biceps brachii muscle for a class project. Now im interested in constructing another EMG circuit with better signal to noise ratio and a clearer EMG signal output with no (or very small) delay. I have attached the schematic of the EMG circuit i had constructed (forum_schematic.jpg) together with the oscilloscope outputs for the band pass filter stage (forum_schematic1.jpg), precision rectifier stage (forum_schematic2.jpg) and finally smoothing low pass filter stage (forum_schematic3).. Could you guys please give me some advice on how I can construct a better EMG circuit than this one? My purpose of constructing this circuit is to measure EMG from forearm muscles (brachioradialis, flexor digitorum superficialis, Extensor Carpi radialis longus) and relate it to hand grip force measured using a hand dynamometer.. Thanks! Would really appreciate feedback,comments or questions =)

 

[KeepItSimpleStupid]

Small value resistor (100 ohms) in series with the non-inverting input of U2.
Change C1 to a polypropolyne cap at a minimum.
Add bypass caps on the supply rails close to the OP amp (0.1 uf Tantalum)
Not sure what type caps you used in the rest of the circuit.

Loose the LF351. Not sure what to replace it by. How about an AD743.

 

[working_on_EMG]

Thanks allot! Really appreciate your feedback.. Im planning to loose the LF351 and replace it with a higher quality Texas Instruments OPA 2604. In this circuit all the capacitors are ceramic capacitors except for the 1 uF capacitor at U5, this one is a monolithic capacitor. This monolithic capacitor is used together with a resistor to form a 'smoothing low pass filter' which smooths out the spiky EMG signal to give a sinusoidal like signal that is suitable to be inputted to an arduino microcontroller.

 

[KeepItSimpleStupid]

I think the choice of caps is your biggest issue. Metalized film or Polypro (more expensive) for frequency setting. The tolerences for these caps are much smaller.

Bypassing is very critical. It needs to be done very close to the op amp body. You can sometimes do better paralleling different types of caps for bypassing. Say a 1 uf tantalum and a 0.1 uf metalized polyester. These caps are used at the power supply pins of the op amp.

Driving capacitive loads can be really troublesome. I'd take a look at each stage with a scope. But remeber, the scope changes the performance too. If you really have trouble driving lots of capacitance, see the app note for the LT1010.

I'm not sure what the better choice forthe OP amp is, but definately loose the LF351.

 

[KeepItSimpleStupid]

You might find this article on bypassing useful: https://www.electro-tech-online.com/custompdfs/2010/12/an1325.pdf

 

[working_on_EMG]

Very useful article indeed! thanks allot.. I understand bypassing much better now

 

[djomgoue]

helo i need hep please im constructing a EMG and all i have is a square wave when i contract the muscle so please a want to see how u puting ur electrodes.i am using a lm358 to amplified is it ok?
thx

 

[djomgoue]

on ur circuit i cant see wer u ll put the electrode

 

[0930005]

Hello! Im also constructing an EMG, i want it for a PID control. I have some questions, does the stages 1,2 and 3 are the inputs and the reference respectively? Do you have your final diagram man? It would help me a lot. Thank you.

 

[grandkyle]

where is the input and reference electrodes supposed to go.

and could you please add more detail on your circuit please

 

[neenunair]

Hai...please help me to construct an EMG Circuit.I need the explanation of the circuit too...Mt time is very short...plz help me to complate my final year project.