|Light activated switch circuit|
Light activating and deactivating switches are simple to build when you are provided with a LDR (sensing element) and 555 (switch activator). These kind of sensor circuits are widely employed in many applications and may come in handy when you intend to build a simple light sensing circuit. LED is used in the above circuit to indicate switching, you can use device of your desire provided ample amount of power supply.
WORKING OF CIRCUIT:
The circuit comprises of two divisions one is LDR , the light sensing element and another one is 555 activator. The LDR is paired with Resistor R1 to form a potential divider to feed the trigger voltage to the IC 555. It gives maximum voltage when no light is incident in it and minimum voltage when light falls above LDR.
|Setup of Light activated switch|
The activator is build around a 555 IC which was wired as a monostable multivibrator. Monostable Multivibrator gives a high output in the presence of negative trigger at the pin 2 whereas low output in the presence of positive trigger. This principle was used here to make the 555 acts as a switch when light incident in LDR.
When there is no presence of light the potential divider gives a positive trigger to the pin 2 of 555 IC. This results in low signal output at the pin 3 of 555. Incident of light in LDR makes the potential divider to give out negative trigger to the second pin of timer IC and this in turn forces the output at pin 3 to go high. Thus the combination of LDR and 555 works as a light activated switching device.
- To Switch high power devices such as Relay, speakers etc use transistors to turn it on by drawing power directly rather than sourcing it from 555.