I see what you mean. I've also zoomed in on the signal to show that better:
However, on a larger time scale, there is about a 0.75 - 1Hz slow frequency sinusoidal drift of the amplitude that I would also like to preserve.
This signal is actually the output from a standard pulse oximeter, and I am fairly certain there no filtering performed on it before it enters a patient monitor. The two overlapping square wave portions of the signal is from a phototransistor, receiving light signals from a red and IR LED that is switching on and off at 166Hz. The slow frequency drift actually contains information about the heart rate and needs to be sent to the monitor as well.
Because the monitor is super sensitive, I want to emulate this signal as close as I can with the Arduino. Therefore, if I would prefer to go the route of having a downstream DAC, where would I begin and how do I choose an appropriate component for this application?
Thanks again for any assistance!