Laser Beam Light Activated Remote Control Circuit

The following post illustrates a simple light toggled/operated remote control circuit, which can be activated by an ordinary flashlight or more effectively through a laser beam unit (key chain type). 

Circuit Diagram : 

                                                  

The circuit idea may be understood with the below mentioned points:

• Transistor T1 alnog with R3, C6 and the LDR itself forms a simple light sensor stage. 
• The LDR is connected across the base of the transistor and the positive supply such that when light falls over the LDR, T1 receives the required base bias and conducts. 
• When T1 conducts, the high potential at pin 14 of IC1 is pulled to logic low. However since a logic low wouldn't effect pin#14, IC1 does not respond as yet.
• The moment light on the LDR is switched OFF, T1 is switched OFF and pin#14 now instantly receives a subsequent logic high via R5.....now IC1 responds, and shifts it's output from pin#3 to pin#2. This makes pin#3 logic low, activating T2, and the preceding relay driver stage.
• The above condition persists until the LDR is illuminated again with a flashlight or with a laser beam.
• The above operation alternately toggles the output ON and OFF providing the required toggling actions to the connected load.
• The LDR must be covered inside an opaque pipe, about an inch long so that the ambient light stays obstructed from the LDR.
• The angle of the pipe should be kept in a such a way that it facilitates easy focusing of the light beam toward the LDR. 
• C6 ensures that the system does not respond to accidental spurious light beams in case it finds its way inside the pipe, and over the LDR.

Parts List


R3,R4,R5,R6,R7 = 2K2


T1 = BC547,


T2 = BC557


IC1 = 4017


IC2 = 7812


ALL DIODES = 1N4007


C6,C7 = 10uF/25V


C8 = 1000uF/25V


C10 = 0.1uF

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