I'm building an EMG for my biomedical design class and have ran into issues with biasing the AC signal. I do all of my amplification/filter stages with op-amps powered using +/- 9V. Once all the signal processing is done, I put it through a DC-biasing circuit to get a DC offset of +2.5V before I send it to an analog pin on the Arduino Uno. The bias level is set using an op-amp voltage divider powered by the Arduino 5V connection. Unfortunately, this doesn't seem to be working as planned. The bias level seems correct (it's not quite at 2.5V but I'm guessing there is a little common mode voltage in my signal), but I get weird clipping at ~1.5V on the bottom end and ~4.5V on the top end. Below is a link to that part of the circuit.http://imgur.com/GfwOI
I would just like to know why I'm experiencing this strange clipping. If you need any more information feel free to ask.