If you want to compare two LDR's, you could put them in series like a voltage divider and measure the node where they connect, opting for half the A/D-C reference voltage.
This will need LDR's with a sufficiently high resistance (in the brightest light they see) to keep the current to manageable levels, or they'll die when brightly lit!
Hi, I decided to dump the whole idea of a/d-c in my microcontroller as in the first place, I don even know where to start! It was a mistake for me to choose microcontroller at the 1st place so I planned to keep my programming really simple.
in the end, I decided to use 3 LDR connected in different parts of the robot( ie: left, right ,middle) and the programming in the Microcontroller is right.
Left LDR sense light = car turns left
Right LDR sense light = car turns right
Middle LDR sense light = car moves forward
I tested it out with LED's and it worked fine like the steps mention above. but when I replace the motor( with H-bridge) directly with the LED's, the "move right" works fine, the "move forward" moves surprisingly slow, and the "move left" doesnt work at all!!
So I am wondering if there's anything else I could add.. Is LM339 a vaiable option.