Hi guys,

I am trying to design the EMG circuit using INA121P and OP07 Op-Amps.

I understand that EMG will need a preamplifier before any filtering is done, so i looked on the Internet and found preamplifier circuit in the data-sheet of the INA121P itself. (Schematic attached below)

I've built this circuit on a breadboard and now I want to check if it works.

In order to check it, I connected the +ve electrode of the EMG cable to O/P of my function generator giving out the positive pulse of 20Hz and 1.28V Amplitude and grounded both Ref and and -Ve electrode. (Is this approach right at all?)

However, the o/p of the preamplifier is not what desired, instead it is giving out a constant 7V O/P (Supply voltage for the INA and Op=Amps is +/-9V)

I know that I might be horribly wrong with this approach, but please bear with any mistakes I might have made and help me solve this problem!!

Thanks!!

*I didn't get OPA2131 in the local market that's why i went with OP07!

 

Please post a schematic of your circuit (not attached to your post!) otherwise we would just be guessing.

 

Please post a schematic of your circuit (not attached to your post!) otherwise we would just be guessing.

I've edited the post and attached the cicuit now, I've built the exact same circuit shown, only difference is instead of OPA2131 I've used OP07.

 

Hello,

Where is the schematic?
How is the INA powered?
It must use a dual powersupply.

Bertus

 

I am attaching the hand drawn schematic of the circuit!!
Thanks!!

 

The diff amp is running at a ***differential*** gain of 10. If you ground one input and put 1 V on the other, the output will try to make 10 V and will saturate. Reduce the output of the function generator to 0.1 V peak-to-peak and see what happens.

ak

 

To test a differential input amplifier, you can use a pulse transformer with centre-tap secondary winding. Connect the centre-tap of the secondary winding to GND (circuit COMMON).

Or something like this: