Been working on the two stage opamp for my Sundar. The first stage takes the current from the photodiode and turns it into a voltage with a certain amount of gain. The second stage applies a second gain as well as an offset via two digital (SPI) potentiometers.
The first set of opamps I uses were 741s I had around. They did not work because the need +-9V and I am running on a 5V rail. The next set I picked up from Radio Shack were a bit better but still were not rail to rail. Next set I ordered from Digikey were rated rail to rail in the title, but only later did I find out that was only the case for larger voltages.
Last set I am working on (again from digikey) was designed for low voltage but although the input is rated rail to rail, the output still is not.
So after careful consideration and talking to every EE I know, I placed an order for some expensive opamps from Linear Technologies. These are rated for a single 5V supply with railt to rail inputs and outputs. Hope these work when they arrive early next week.