As I mention before surface electromygraphy(sEMG) is bio-electric signal which is come from human muscle unit. This time I’m going to introduce making a circuit to extract sEMG from human body and how to find muscle location for sensors.
1. Muscle location
Actually, It is very hard to find muscle location to general persons. Most of people don’t know much about muscle structure and mechnism. So I suggest this site which constructed by google(yeah it is free!) http://www.zygotebody.com/
this site shows anatomy of human body. you can estimate location of muscle by using this for example if you want to know muscle which is connected to knee, you can click and see just like this picture.
you can find the name of muscle and it’s attached bone. after that you should attach sensors to your body. Usually bone area is ground.
the picture shows how to attach sensors to bicep muscle.
2. Circuit for EMG signals extraction
Circuit of EMG signal extraction is very simple. There are three step for circuit.
Instrument amplifier is for amplify the EMG voltages. I usually use AD620 for this but you can use INA series else. The gain is modified from data sheet of your device.
Active filter part. This one is 1st order of active high pass filter. Cutting frequency is calculated by f=1/(2*pi*c2*r4). Amplitude gain is Gain=r2/r4. In this circuit cutting frequency is 19.175Hz and gain is 4.699
Finally we are doing low pass filtering. This one is also first order active lowpass filter circuit. It’s cutting frequency is f=1/(2*pi*c1*r1) and gain is Gain=r1/r5. In this circuit cutting frequency is 530Hz gain is 3.
I made three EMG circuit and this is for forearm muscle’s EMG signals. You can change cutting frequency as you wish. It is quite diffrent cutting frequency for purpose
Next time I’m going to go introduce ADC of EMG signals usually used method for preprocessing.