amplifierarduinobiopotentialdc-offset
i try to build emg sensor + arduino from diy found on internet.
every things work fine, but i want only raw signal for some bigger project not rectify. i do circuit as below
and signal looks like
as you can see when it reaches value 0 it stops. i try to get some real raw signal and modify code, but nothing change, so i think it's hardware. any guess how to remove this offset ? configuration of tl072 should be different?
The critical point here is to control the ground of the phone.
When you manipulate your phone for its normal usage, one hand is touching it and sets the ground. Trying to do the same manipulation with a phone sitting on a table will be less reliable.
To have the same effect in the lab, you should have your phone laying on a conductive layer that is connected to the ground (or any other fixed potential) of your circuit. A simple way to do so is to have your phone laying on a copper foil that is used as the common ground of your circuit.
Your phone does not need to have direct ohmic link to ground, a good capacitive coupling is ok too.
Best Answer
You need something like this:
simulate this circuit – Schematic created using CircuitLab
That adds 2.5V to the AC signal. It also inverts the AC, but I don't think that will bother things.
Depending on how you have your existing TL072 connected, you could probably do this all in that one stage.
But, you didn't post your schematic and I don't feel like drawing one from your breadboard sketch, so I'll just leave this as is.
You've got 5V on the Arduino, but it is usually very noisy. I've used 5V in the schematic just to make it clear that you need a regulated voltage. The two 9V batteries aren't regulated, so you can't generate your 2.5V from them.
You might be able to use the Arduino 5V if you use a large enough value for C1 to clean up all the noise. I've put a 1µF in. That ought to do as a starting place.