my friend i tried many times to do this emg circuit i replace the instrumentation amplifier (AD8221) with ( INA 129 ) by considering the differences in the pins number , but it doesnt work , please i appreciate your help , thanks in advance .
Doesnt work? Do you mean there is no signal output at all? What input signal are you testing it with?
i connect the analoge pin to the arduino but give me very bad result like 0 then randomly 1023 , i used electrode as inputs
mohammadgh95:
i connect the analoge pin to the arduino but give me very bad result like 0 then randomly 1023 , i used electrode as inputs
Did you adjust the IA's gain setting resistor when you switched to the INA 129?
Are you connecting the circuit's ground to the arduino?
Have you checked the +Vs and -Vs voltages with a multimeter?
i connected the circuit ground to arduino but i didnt adjust the IA's gain setting resistor and i didnt checked the +Vs and -Vs ,please could you please explain for me how to do these steps i am not elctronic engineer i am biomedical student , any hint will help me ,
thanks in advance and for your reply 
mohammadgh95:
i connected the circuit ground to arduino but i didnt adjust the IA's gain setting resistor and i didnt checked the +Vs and -Vs ,please could you please explain for me how to do these steps i am not elctronic engineer i am biomedical student , any hint will help me ,thanks in advance and for your reply
The AD8221's spec sheet will have an equation to find the gain. Enter the resistor value on the circuit diagram into this equation to find the gain.
Then use the gain equation from the INA129's spec sheet to calculate the resistor value you need for the INA129's gain to match the AD8221's gain.
G = 1 + (49.4 kΩ/RG) gain equation for AD8221
G= 1+ (49.4 kΩ/RG) Gain equation for ina129
they have the same gain equation but i have problem in the potentiometer i couldn't plug it on the breadboard correctly , and i was not able to decide the value of it , should i connect potentiometer to thee ina or the RG is enough
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