Hi , i got a photodiode somewhere and i dont have its datasheet i connected it as a common emitter , used a 10k resistor , illuminated it with red led . i want to use it as a line follower sensor , to detect white and green surfaces , i used an LM324 for this purpose , i found that the distance between the reflected surface and the photo diode while using the red led is so small less than a cm , dont know what to change ? reduce the 10k ? also the swing voltage from a full room light and with my hands conver the photodiode is so small like 33mV .. is this a good swing ?