Hello

I'm working on a project where I need to capture raw sEMG signals to predict the movement. I've attached my current schematic, it's single supply 5V.

The signal comes from the electrodes and goes into the instrumentation amplifier. I've AC-coupled the inputs with a HPF at 5Hz, I found that part of the circuit in a paper. I'll set the gain of the in amp at +- 60dB and the reference voltage at Vmid. After that it goes through a HPF (@10Hz), a LPF (@500Hz), an inverting opamp (gain = ?, I'll try to match it with the 0-5V input range of the analog input of an arduino board) and at last a LPF (@500Hz).

I have 2 questions that I'm unsure of.
1. I need to bias the inputs of the in amp at Vmid so that the signal is in the operating range of the in amp. Do I do that at the inputs itself or split the Rg resistor and add the bias voltage there. I've seen both.

2. Where do I connect the Vref electrode? After or before the buffer IC3A or split Rg resistor and add there.


For the rest, I think my schematic will work. Other comments are appreciated.

Thanks

 

Hello,

The circuit will not work as the supply voltage is to low for the TL084:



It will need at least 10Volts to work.

Bertus

 

Thanks for your response. Yeah, I'm not going to use those. I'm going to use the TSV914. http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00127596.pdf
The import in eagle was a block schematic instead of those single amps which I find easier to use.

At the moment I'm going to connect the reference electrode to the 'ground' plane which I set at 2.5V. The two inputs I'll bias at 2.5V aswell.

 

Hello,

The following page will give you information about the use of Vref:
http://www.analog.com/en/analog-dia...oblems-when-designing-amplifier-circuits.html

Bertus

 

I was talking about the reference electrode. Maybe my naming is not consistent. But Vmid is 2,5V, Vcc is 5V and Vref is the reference electrode connected to my body. E+ and E- are the other 2 electrodes.

This is the current circuit for the inamp. What I don't fully understand yet is that by connecting R3 and R4 to Vmid, I bias my inputs, according to the article and I don't need Vcc to do it.
I'll use the LP3990 lin voltage regulator, http://www.ti.com/lit/ds/symlink/lp3990.pdf

 

Hello,

From the posted schematic I see that you have used the tsp77018 ( an 1.8 Volts regulator ) to set the Vref on 1.8 Volts.
This will give a difference between Vmid of the electrodes and Vref.




Bertus

 

I'll use the LP3990, I didn't found a schematic for eagle.

 

Hello,

Wich version of the LP3990 are you using.
The datasheet shows that there are versions from 0.8 Volts to 3.3 Volts.

Bertus

 

The 2.5V one, http://be.farnell.com/texas-instruments/lp39902-5-nopb/ldo-fixed-2-5v-0-15a-sot-23-5/dp/2382971.