It's been a long time since I did anything electronic, but I finally sat down this weekend and got the photocell light sensor put together to control a set of motors. The point of this is so a simple robot can roll forwards until the photocell goes dark when it hits something, then it can turn and back up before continuing again.
I'm using an op-amp to detect when the light passes a threshold, and it took some playing with to get it to interface with TTL logic so I could get some inverters to provide linked Forward and Backwards signals to send to an H-Bridge to control the motors.
At first I was trying the recommended resister values between the op-amp and the inverters, but got nowhere with getting that to work, but after some experimenting I got some completely different values to work. I need to refine the circuit to get rid of both the potentiometers, but at least it works now and I can control the motor direction by shading the photocell. I'll also remove most of the indicator LEDs once I've got everything refined.