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).
The circuit idea may be understood with the below mentioned points:
How the Circuit Functions
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.
Circuit Diagram
Parts List for the above light operated remote control circuit
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
PCB Layout
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Hamed Hosseinian says
Good
Dondon says
Hi Sir Swagatam, I need a circuit similar to the circuit above but I will use the LED of mobile phone as light source so I can turn ON and OFF the load using mobile phone. The load will be activated only after two rings of the phone, after 1st ring the device will wait for the 2nd ring within 2 or 3 minutes or else the 1st ring will be discarded to avoid unintended triggering of the load. If possible the supply of the 4017 IC is 3.7V so I can connect it to mobile phone battery to preserve the output state in case of power interruption, the relay section can be connected separately to 12V so it will not drain the phone battery.
Thank you Sir in advance and more power to you!
Swagatam says
Hi Dondon, I'll try to design the required circuit, and let you know once it gets published
Sridhar says
Hi How to make a simple ir sensor circuit
Heeran Manilal says
Hi, I have built many of your amazing circuits but the laser circuit does not seem to work, there are no changes when the laser is aimed to the LDR. I have built the circuit twice and still no results. I require a circuit that can work like and on off light switch but controlled by a laser.
Thank you.
Swagatam says
Hi, remove R3 and then check. When light falls on the LDR, pin14 potential should become zero, and as soon as the light is switched off, pin14 should become high in potential and consequently result in switching of the output.
Siva says
still its not working
Anonymous says
Dear sir, im new to this field. Can u pls tell me what is Load in that schematic diagram.
Swagatam says
load can be anything like a light, a fan or a TV etc.
Anonymous says
Hi Sir,
What is spec of transformer: P- 0-220 / S- 0-12v? or can i use 12-0-12 for secondary coil?
What about the relay's value?
Thank you very much.
Swagatam says
0-220 is the primary, 0-12 is the secondary of the transformer.
you can use one of the taps (0-12) from your 12-0-12 trafo
relay coil voltage should be equal to the transformer voltage value, and the contacts rated to handle the load current.
Anonymous says
Using a Transformerless power supply & a Triac to drive the Load perhaps will be more simpler and less power-consuming for this project! Can I request you to re-design the circuit?
Swagatam says
Yes it can be done, I will try to update it soon.