Hi, James.
Yes, this topic is related with the motor control topic I posted earlier.
Actually, I never used any ir sensors or photo dectors before.
This is the first time, so I am trying to use both diodes and transistors for my learning experience.
There is no special reason for me to use both of them.
I just hope that I could use them as a switch. Detector as a switch and emitter as a trigger element.