https://www.instructables.com/id/Muscle-EMG-Sensor-for-a-Microcontroller/
I am working on EMG Signal Acquisition for further analysis of acquired data on MATLAB.I have referred to the above site for EMG signal Acquisition Circuit, i have replaced Differential amplifier (INA106) with AD620 due to availability issue of IN series here. It is showing straight line at the output meanwhile not providing any kind of results or sometime it generates random signal. I have following questions regarding this project:
1- Which IC is a good replacement for INA106 other than IN series?
2-Which is the correct location of muscles for placement of electrodes?
3-How can we assume our EMG signal is accurate?
PS:I am using ARDUINO IDE for results visualization.
I would highly appreciate If anyone can give suggestions that can help me to acquire EMG signal accurately.
The circuit diagram is given below.

 

Welcome to AAC.

Check out this thread: https://forum.allaboutcircuits.com/...ential-amplifier-by-texas-instruments.147346/

 

hi J,
Welcome to AAC.
Do you have a section of the circuit showing how you have the AD620 connected.?
E

 

hi J,
Welcome to AAC.
Do you have a section of the circuit showing how you have the AD620 connected.?
E

INA106 and AD620 have same pinout configuration, so I have connected same like the INA106 in circuit diagram.

 

hi,
How have you set the Gain of the AD620.?
E

Added:
AD620 ECG cct.

 

hi,
How have you set the Gain of the AD620.?
E

Added:
AD620 ECG cct.
View attachment 174952

have not set yet..

 

hi,
The INA106 has a fixed gain of 10, the AD620 requires the gain to be set by Rg, you cannot simply replace the INA106 with a AD620.

Please post a sketch of the AD620 connections.
E

 

hi,
The INA106 has a fixed gain of 10, the AD620 requires the gain to be set by Rg, you cannot simply replace the INA106 with a AD620.

Please post a sketch of the AD620 connections.
E


I have considered the gain and have made the following changes in connections.

 

hi,
The original gain of the INA106 was 10, if you now increase the gain of the AD620 to 110, the following OPA circuitry could be over driven and give incorrect operation.

E

 

hi,
The original gain of the INA106 was 10, if you now increase the gain of the AD620 to 110, the following OPA circuitry could be over driven and give incorrect operation.

E

The required gain was 110 in the first phase of circuit , as shown below

 

hi j,
What are the problems you are getting with the circuit not operating as expected.?
E

We can model the project in LTSpice when you are ready.

 

hi j,
What are the problems you are getting with the circuit not operating as expected.?
E

We can model the project in LTSpice when you are ready.

yes sure we can model it and the problem is I guess in the placement of electrodes.

 

hi j,
What are the problems you are getting with the circuit not operating as expected.?
E

We can model the project in LTSpice when you are ready.

sir i've tried the changes, but still getting a straight line .can you please provide few suggestions?

 

hi J,
Do you have a scope to check for any signal appearing on the output of the 110Gain and the -15Gain OPA's.?
Also how are you driving the inputs of the AD620.?
Please show the input source circuit.
E

 

hi J,
Do you have a scope to check for any signal appearing on the output of the 110Gain and the -15Gain OPA's.?
Also how are you driving the inputs of the AD620.?
Please show the input source circuit.
E

yes I am driving the input of AD620 through electrodes the number 2 and 3 of AD620 are inputs connected to end of muslce and mid of muslce.
something just like this:

 

hi J,
Where is the Common reference for the muscle connections.?
ie: what is the common mode voltage for those input pins.?
Measure the voltage on the input pins, what is it.?
E

 

hi J,
Where is the Common reference for the muscle connections.?
ie: what is the common mode voltage for those input pins.?
Measure the voltage on the input pins, what is it.?
E

common ref is connected to ground, and sir can i have your mail address?

 

hi J,
It is difficult to help if you do not post answers to my questions.

Do you have a scope to check for any signal appearing on the output of the 110Gain and the -15Gain OPA's.?
Post what voltages you measure on those two outputs.
E

 

hi J,
It is difficult to help if you do not post answers to my questions.

Do you have a scope to check for any signal appearing on the output of the 110Gain and the -15Gain OPA's.?
Post what voltages you measure on those two outputs.
E

Actually i am student and i don't have Oscilloscope and Multimeter available at home but yes i can check the output using Osciloscope in LAB and same for the voltage i'll measure this tomorrow and will inform you right away.

 

hi,
OK . I understand.
First do this test:
Connect the two inputs of the AD620 together and connect them to 0V, the AD620 output voltage should be almost zero volts.

If the output is zero volts, now check the output of the second OPA, it should also be close to zero volts.
Let us know what you measure.
E