Dear Arduino friends,
I am trying to make an electromyography project these days and I have a little problem. I made an EMG schematics using a simple AD620 amplifier and, when connected to the soundcard or the oscilloscope, it works very fine. It shows up and down waves when I contract the investigated muscle. But when I connected the same input to one analog input pin on my Arduino, it dows not work at all. When started, it gos from 1023 down to 0 regardless of the muscle contraction and it stops there, not reacting anymore. How could I remediate that, it is very annoying to now that your circuit works, but it cannot be read. I also posted a picture of the EMG circuit (imagine the electrodes placed on a muscle, not on the limbs, like for ECG) and a capture of the EMG signal collected with a soundcard. It works like that, but not on Arduino.
the arduino can do 0V..5V...
and ur amplifier output seems to use a charge pump that produces -6V to 6V... via a quite fat 1mF cap...
maybe that much charge damaged the protection diodes of the arduino or the arduino input...
u could try to connect the arduino's ground to -6V... (hopefully it is a battery?)
and then use a voltage divider that brings the voltage below 5V...
what does the oscilloscope say about the peak voltage?
Ok, thank you for both answers. Peak voltage is about 3V. I do not know the exact scale of the chart, but on x scale are a few seconds and, as I said, the peak voltage is around 3V.
What if I use a rectifier bridge on output of the myograph?
A lot depends on what info you need from the pulses? Magnitude, freq. of sub-carrier, period of pulses, magn. both negative - positive, decay time etc.
a rectifier bridge would work,
if u dont share the GND between the arduino and ur amplifier,
and if the absolute values r sufficient (the negative parts would show up as positive...)...
why cant u connect arduino ground to the negative supply rail of ur amplifier?
then u just need a voltage divider...
I will try the second, connecting the negative to the ground and tell you if it works.
But if I were to use a bridge, where should I connect the GND of the myograph, if not to the GND of the arduino? I did such last night and it did not work.
No, I did not use a resistor, but, hopefully, my arduino pin didn't burn. It looks ok, I teste it with a potentiometer. I will retry ith the bridge and use the negative of the bridge to connect to the arduino GND. I'll get back to you soon.
Hello claudiu_mirescu i wrote your post and i hope you got the right answer.
I started with the same topic today: building an EMG Circuit for measuring muscle-contraction.
My problem is i have no idea how to start. Can you help me step by step how i can get the circuit on a board?
The Devices i need to the construction, is also my problem. i dont know what devices i need.
Thank for your aid.
I also work on same type of project, But i want to know about Electronic circuit power supply. In my case, when i give power supply AD620, In outpin of amplifier gives -5V. How to connect circuit. Please help me on regarding issue. My email ID:- thumar.rushik@gmail.com