Transimpedance amplifier

Hello Arduino hackers!

I have set up a photodiode with an opamp and a reverse bias to measure the amount of light it receives (see Figure 13: http://saaubi.people.wm.edu/TeachingWebPages/Physics252_Spring2007/Week10/Chapter10_OpAmpCircuits.pdf )

It works very well with the exception that the voltage at the output goes down when the amount of light goes up. While this could be easily compensated for on the software side, I was wondering if there is a simple way to adjust this on the hardware side so that more light equals more voltage?

Unfortunately at this point I have no idea how exactly a transimpedance amplifier works and whether it might just be enough to switch the inputs or something like that to adjust the signal.

Maybe someone who knows a bit more about electronics than me could give me a quick tip on this?

Thank you very much & have a nice sunday! Tom

There are two options: 1). Use second OPA as it shown on Fig. 1 to invert signal; 2). Don't use OPA at all, input resistance of the arduino analog pin 100 MOhm, Connect diode and resistor according to Fig. 12 Probably, you will have to adjust value of the resistor, depends on ambient lighting conditions. I'd suggets to start with 1 MOhm, and decrease it, if analogread gives a digit not in the middle of the range ( 512 for + 5V ).

Thanks for the info Magician!