This circuit is a laser controlled relay switch with timer that can be made using readily available components. This laser switch has the following advantages :
- Timed operation - Turn on time of the switch can be controlled
- Large current handling capability, can control a motor
- Stand by and operating mode led indication
- operating mode Piezo alert.
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| Circuit Diagram of Laser Switch With Timer: Click to enlarge |
Here we can use a laser diode as a light transmitter or you can use any other laser pointer. In this laser switch the laser diode LED1 is protected by diode D1, and resistor R1 from over current flow.
Working Principle
When the laser beam produced by laser led falling on T1 photo-transistor, it conducts and reverse biases transistor T3 thereby making input of gate N1 of IC1. This makes stand by led driver T4 to conduct and the green led indicating stand by mode will glow continuously.
If anyone interrupts the flow of laser beam to T1, it stops conducting and T3 becomes forward bias and standby led will turn off (output of gate N1 will be low). Simultaneously, the low output of gate N1 makes the output of gate N2 high. This triggers triggers the monostable multivibrator employing gate N3 and N4 of the IC1. Resistor R8 and capacitor C1 determines the time period. This triggers the second monostable built around IC CD4538. As a result, relay RL1 get activated. This operating mode is indicated by LED3. Also piezo buzzer produces an alert that the relay is turned on.The transistor T5 is used to drive the relay and T6 is used to drive the intermittent piezobuzzer.
The turn on time of the laser switch can be controlled by the preset VR2. This controls the time period of second monostable.
Notes:
- IC1 is a CD4001 (N1-N4) gates.
- Circuit works off 12V dc supply
- Regulator 7805 makes sure the proper working of CMOS IC's.
If you have any doubts, please mention it in the comments field.
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