I'm trying to build an optical power meter using a photodiode in photoconductive mode and a LM324N OpAmp:
However, the output voltage signal is very low. Exchanging R_f for a smaller resistor or even shorting it gives a higher output. According to https://en.wikipedia.org/wiki/Transimpedance_amplifier, V_out / I_in = -R_f, so I would expect a smaller R_f to decrease the gain, not increase it.
Please help me understand what I'm doing wrong.