The light-sensitive switch is an ingenious electronic device that responds to the intensity of light falling on it, enabling the automatic switching of lights. In this article, we will explore a simple, cost-effective, and user-friendly light-sensitive switch circuit utilizing the popular op-amp 741. This circuit operates based on light sensing, intelligently turning lights on or off according to the ambient light conditions.
Description of Light Sensitive Switch Circuit using Op-Amp 741
To delve into the intricacies of this circuit, let’s divide it into two sections: the power supply and the switching circuit.
Power Supply Section:
In the power supply section, The rectification of AC mains to DC is accomplished by bridge rectifier design using four general purpose rectifier diode D1 to D4 whereas the function of the step-down transformer is accomplished by resistor R1, and the ensuing regulation to generate a 10V DC supply is facilitated by the zener diode ZD1. The filtered output voltage from the zener diode is further stabilized using capacitor C1.
Switching Section:
The switching section revolves around the light-dependent resistor (LDR1) and the operational amplifier IC 741. The LDR acts as the sensor for the switching circuit, exhibiting changes in resistance in response to variations in light levels. By manipulating the position of a switch, we can make this circuit either light-sensitive or dark-sensitive, enabling it to turn on in the presence of light or in the absence of light, respectively.
The varying resistance of the LDR is sensed by pin 2 of IC1 (operational amplifier), which is then finely adjusted using preset VR1. The resulting output is obtained from pin 6 of IC1 and routed through resistor R6 to the base of transistor T1, with resistor R7 serving as a current limiter. The output from the collector of transistor T1 is subsequently connected to the gate of TRIAC1, which effectively controls the lighting load.
Light Sensor Functionality:
To utilize the circuit as a light sensor, connect the switch SW2 to Vcc and switch SW1 to GND. This configuration enables the circuit to activate the connected bulb when light falls upon the light sensor.
Dark Sensor Functionality:
Conversely, to harness the circuit as a dark sensor, connect switch SW2 to GND and switch SW1 to Vcc as shown in the circuit diagram. In this setup, the circuit illuminates the connected bulb in the absence of light. Light-Sensitive Switch Circuit Using Op-Amp 741
COMPONENT LIST OF LIGHT-SENSITIVE SWITCH CIRCUIT USING OP-AMP 741
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 100 KΩ/1W
R2, R3 = 100 KΩ
R4 = 4.7 KΩ
R5, R6 = 220 KΩ
R7 = 68 KΩ
R8 = 33 KΩ
VR1 = 100 KΩ (preset)
Capacitor
C1 = 100 µF/16V
Semiconductors
IC1 = LM741 (Op-amp)
T1 = BC547
TR1 = 10GD (Triac)
D1 – D4 = 1N4004
ZD1 = 10V /100 mW
Miscellaneous
LDR1 = Light Dependent Resistor
B1 = 200W bulb
Conclusion:
The light-sensitive switch circuit using the op-amp 741 presents an efficient solution for automating lighting systems based on ambient light conditions. By integrating the capabilities of the op-amp and the light-dependent resistor, this circuit enables seamless and intelligent control over the connected lighting load. Whether it’s a light sensor or a dark sensor, this circuit offers versatility and reliability for a range of applications.
Some issues: 1) That the current design uses its own full-wave rectifier to provide power is nice, but is a potential shock hazard; It would be better to eliminate the power supply section and use an external power brick instead. 2) Though the circuit will work as described, there are a number of areas that could be improved: For example, the circuitry that drives the triac could be redesigned to turn on an isolated relay. That relay could be used to turn on a lamp using either 220v mains voltage or from a battery source. As it is now, the current design will work but would never pass safety requirements. But it’s a useful circuit and can be modified as described to make it safer and easier to build.
Hi Pete, Thank you for the suggestion. Previously, we had already posted different circuit based on LDR. Major consideration for designing this circuit is price and size. In order to lower the cost and reduce the size of the project we eliminates the use of isolated switching circuit and using external power bricks.
This circuit can be used in street lamp.
Isn’t this what is commonly called a dusk to dawn sensor?
Beside sensor we are also switching the load and you can configure this circuit according to your requirement like dusk to down sensor or vice-versa by selecting switch.
Thankyou