1. Go to your local RadioShack and purchase the following: 2 - Cds Cells (Photocells), 1 - 741 Op Amp, 1 - 1 kilo ohm resistor and LED, 1 - 9 volt battery breadboard, 1 - 10K potentiometer
2. Take the bread board and put the 741 Op Amp in the middle, shown in the picture below.
3. The next steps can be seen in photo above.
4. Nodes, if looking at the breadboard vertically, are horizontal and do not continue beyond the break in the middle. So there are two different nodes horizontally across each row of the breadboard.
5. The 741 Op Amp has 8 pins, 1 through 8. Pin number 1 will be the one closest to the little circle in the corner and 2 through 8 will be counterclockwise from there.
6. After placing the Op Amp on the breadboard, put one pin on a Cds cell in the node connected to pin two of the op amp and the other Cds pin in the seventh pin of the op amp. The other cds cell likewise connects to pins two and four of the op amp.
7. Connect the middle pin of the potentiometer to pin three of the op amp, the right pin of the pot. to pin seven of the op amp and the left pin of the pot. to pin four of the op amp.
8. Connect the negative of the battery to pin 4 of the op amp
9. Connect the negative (usually shorter) lead of the LED to pin six of the op amp. Connect the other pin of the LED the 1K resistor. The other side of the 1K resistor should be connected to pin seven of the op amp.
10. Connect the positive battery wire to pin seven of the op amp.
11. All that is left to do is connect the battery, and adjust the pot. as needed.