03-03-2011, 10:30 PM
The automatic street light controller basically consists of a LDR which is used to sense the light intensity. It has high resistivity in the absence of light and very low resistivity in the presence of light. The output of the LDR is directly connected to the relay which actuates and turns on or off the light. In another system, the LDR input maybe fed to the microcontroller, which then appropriately sends out the control signals to the relay turning it ON or OFF.
In the block diagram, the LDR controls two relays, one of them to control odd number of relays and the other to control even number of relays.
For more details, see:
http://scribddoc/23545626/Automatic-Street-Light-Control