This an instructable that shows a way to make a Light detector with a diferent scheme of the classical 555's diagram, that is available in the internet: http://www.555-timer-circuits.com/light-detector....

Step 1: Material

The list of components is:

1 - LDR

1 - CA3140 OpAmp

2 - BC547 NPN-BJT

1 - LED red

2 - LED green

3 - 330R resistors

2 - 220R resistors

1 - 4,7K resistor

Step 2: Schematic

In the computer I've made the schematic of the picture.

Based on the schema of the previous step, I've assembled the circuit in a breaboard, to make the first tests, as we can see in the picture.

After the success of the tests, we can finally mount the circuit, soldering the components in a PCB, or in a pierced board, like I did.

Like the LDR sensor may be used in a distant place of the rest of the circuit, I've soldered in its pins some wires with about 1,5m long.

After that, I've hot-glued the circuit inside a plastic box and we can see the final result in the picture.