Hello Mr. Joseph Lee,

At the below web site your will find a circuit that can senses Dark/Light, which will pick up a Relay. You can use the relay contacts to feed into your 8051 microprocessor to count the amount of DIP IC's flowing on the conveyor belt.

You might even want to simplify the whole process by using an older computer parallel port and QBasic. This is a great resource for people to who don't know much about electronics and assembly software.

http://www.uoguelph.ca/~antoon/circ/actrelay.htm

Good luck,

Charles Bannister