A fotovore is a simple little fotovore that I have been prototyping, it uses two light detectors and two transistor, a PNP and a NPN, to seek the brightest source of light.
The design is simple, the two light detectors are linked together in a series. One side to the + and the other to the - of the battery. The center goes to the two transistor bases. The remaining legs will go either to the motors then negative or to the positive.
You can use anything in replace of the photodiode.
I do not have one built just yet but I have tested the circuit.