6 Automatic Street Light Circuits [using Transistors, IC 555, Solar Panel]
In this article we will discuss 6 useful yet simple automatic street light circuits, which can be used for automatically switching a lamp ON during night time and OFF during day time.
What is an Automatic Street Light System
An automatic street light system is a device which detects the ambient light level conditions and automatically switches an attached lamp ON/OFF depending on the level of the ambient light.
During evening when it is too dark and the light level decreases below the detecting threshold of the device, it turns ON a connected lamp to illuminate the premise.
Conversely, at dawn when the ambient light increases above the detecting threshold of the device, it turns OFF the connected lamp. This automatic ON/OFF switching of the lamp during day and night keeps repeating everyday, automatically, without any human intervention.
The light sensor used in the device is generally a photo sensitive resistor such as an LDR or photo sensitive semiconductor such as a photo-diode or a photo-transistor.
What is the advantage of an Automatic Street Lamp System?
The main advantages of using an automatic street system are as follows:
It saves electricity by ensuring that the lamp never remains switched ON at day time, and is switched OFF when the ambient light condition is adequate to illuminate the streets naturally.
It saves manpower by ensuring that no human intervention is required for switching the lamp ON/OFF manually.
Removing human dependency saves money and time, allowing the system to be very cost effective.
Being an electronically monitored system, the operating accuracy of the device is very high and efficient.
Can we Build this at Home
Yes, you can build a highly efficient automatic street light circuit at home using very few components. Even a newcomer in the field of electronics can build this circuit using very ordinary components such as transistors, resistors and a relay.
However, the person who wants to build this circuit must have all the basic knowledge of electronics and must know how to solder electronic components correctly.
1) Automatic Street Light using a Single Transistor
The first circuit diagram below shows how a reasonably good automatic street lamp could be built using a single transistor, an LDR, a few resistors and a relay.
Parts List
All resistors are 1/4 watt 5% CFR
R1 = 1K
P1 = 10K preset
LDR1 = Any standard LDR
C1 = 220uF/25V electrolytic Capacitor
C2 = 10uF/25V Electrolytic Capacitor
C3 = 1000uF/25V Electrolytic Capacitor
D1----D5 = 1N4007 Diodes
T1 = BC547 Transistor
TR1 = 0-12V/500mA or 1Amp Transformer
RL1 = 12V Relay 200 to 400 ohm coil resistance
LED Bulb = LED bulb 220V/120V, 100 watt or as per street light requirement.
The working of the circuit is simple. During day time when the ambient light is sufficiently high, the LDR has a low resistance. Due to this low resistance it keeps the transistor base more towards the positive level, causing the transistor base at the required 0.6V. The transistor therefore remains switched ON.
With the transistor in the switched ON condition, the relay also remains activated with its contacts resting on the N/O position.
Since the lamp is connected at the N/C position of the relay, the lamp remains switched OFF.
Now, when the ambient light begins to fall during evening and finally reaches a level where the resistance of the LDR increases adequately, the ground potential on the transistor base is raised via the P1, cutting off the biasing potential to the base.
When this happens, the transistor is eventually switched ON. When the transistor is switched ON, its collector becomes active and it deactivates the relay. The relay contacts change from its initial N/O position to the N/C position.
This allows the current to flow through the lamp, and the lamp illuminates.
The next morning, when the ambient light level on the LDR increases, the lamp is switched off yet again, and the cycle repeats itself everyday.
The capacitors at the base of the transistor and the relay ensure that during the transition periods (twilight) or the trip points, the relay contacts do not chatter, rather changeover smoothly.
The potentiometer or the preset can be set appropriately to determine at what light levels the relay is switched ON and OFF.
Remember, while installing the street light circuit make sure the light from the bulb does not fall on the LDR, otherwise that will lead to rapid oscillations of the relay and the lamp.
How to Set up
Keep the preset wiper at the ground level.
Switch ON the power supply.
Illuminate the LDR or the premise with the required amount of light at which you want the relay changeover to happen.
Now slowly adjust the P1 preset until the relay just activates.
Seal the preset with quick-fix glue.
Your circuit is all set now.
Next, test the results by covering the LDR with an opaque shield, you will find the LED bulb switching ON instantly, and vice versa,
2) Using IC 555
Although the above transistorized is simple, its operation may not be too accurate. Meaning, the ON/OFF switching of the relay might not happen exactly at the same dawn/dusk periods.
The second design discussed below uses the IC 555 and overcomes this issue effectively.
Parts List
R1 = 220K 1/4 watt resistor or 1M preset
R2 = 1M 1/4 watt resistor
R3 = 10K 1/4 watt resistor
R4 = 100K 1/4 watt resistor
LDR1 = any standard LDR
C1 = 220uF electrolytic capacitor
D1 = 1N4007 Diode
T1 = BC547 transistor
IC1 = 555 IC
RL1 = 12V relay 200 to 400 ohm coil resistance
LED Bulb = any 100 watt LED bulb or as per the street light requirement
12V SMPS = 1no for powering the circuit
Being controlled by an internal op amp, this IC 555 based automatic street lamp circuit is extremely accurate and will consistently switch the relay everyday, almost at the identical light levels, throughout the year.
Here, the IC 555 is not used in its conventional form, rather simply used as a comparator.
The trip point can set using the indicated potentiometer or a preset R1. R1 can be a fixed 220K resistor if no precise adjustments are required, or it can be replaced with a 1M preset for precise adjustments.
How it Works
During day time when there's ample light on the LDR, the LDR resistance is low, which keeps the pin#2 to ground level causing the output pin#3 potential to be high.
This causes the relay to remain switched OFF with its contacts held at N/C. This in turn causes the light bulb to remain switched OFF.
When night sets in, the light on the LDR decreases causing its resistance to increase. This causes a positive potential to develop on pin#2 of the IC 555, via R1. Due to this pin#3 turns negative triggering ON the relay. The relay contacts now shift towards the N/O turning ON the lamp.
The 555 IC is used as a comparator in this circuit, rather than as an astable or monostable multivibrator. To understand this fairly uncommon use, it's important to understand how a 555 works in general: When input pin 2 receives a trigger (low pulse), the output rises high. This low trigger pulse is defined as a voltage that is less than 1/3 of the supply voltage. When the voltage at the second input, pin 6, temporarily exceeds 2/3 of the supply level, the output goes low again.
Although the second input pin 6 is not used in this arrangement, the chip's output could still flip to the low state since pin 6 is linked directly to the positive supply rail.
By connecting a resistor between pins 5 and 7 of the 555, as illustrated in the circuit diagram the level of hysteresis can be controlled. The level of hysteresis is inversely related to the resistor value, with 100K being a good place to start for research. If R1 is replaced with an 1M potentiometer or preset, the circuit's responsiveness could be adjusted.
Theoretically, the circuit's supply voltage has to be equal to the relay's coil voltage. Nevertheless, do not use more than 16 V since the 555 could well be damaged. At a supply voltage of 12 V, the circuit's current usage, excluding the relay, is 4 mA. The components R2 and C1 guarantee that the relay is powered after a delay of around 2 seconds, making the circuit insensitive to sudden changes in light intensity.
6 Automatic Street Light Circuits [using Transistors, IC 555, Solar Panel]
In this article we will discuss 6 useful yet simple automatic street light circuits, which can be used for automatically switching a lamp ON during night time and OFF during day time.
What is an Automatic Street Light System
An automatic street light system is a device which detects the ambient light level conditions and automatically switches an attached lamp ON/OFF depending on the level of the ambient light.
During evening when it is too dark and the light level decreases below the detecting threshold of the device, it turns ON a connected lamp to illuminate the premise.
Conversely, at dawn when the ambient light increases above the detecting threshold of the device, it turns OFF the connected lamp. This automatic ON/OFF switching of the lamp during day and night keeps repeating everyday, automatically, without any human intervention.
The light sensor used in the device is generally a photo sensitive resistor such as an LDR or photo sensitive semiconductor such as a photo-diode or a photo-transistor.
What is the advantage of an Automatic Street Lamp System?
The main advantages of using an automatic street system are as follows:
It saves electricity by ensuring that the lamp never remains switched ON at day time, and is switched OFF when the ambient light condition is adequate to illuminate the streets naturally.
It saves manpower by ensuring that no human intervention is required for switching the lamp ON/OFF manually.
Removing human dependency saves money and time, allowing the system to be very cost effective.
Being an electronically monitored system, the operating accuracy of the device is very high and efficient.
Can we Build this at Home
Yes, you can build a highly efficient automatic street light circuit at home using very few components. Even a newcomer in the field of electronics can build this circuit using very ordinary components such as transistors, resistors and a relay.
However, the person who wants to build this circuit must have all the basic knowledge of electronics and must know how to solder electronic components correctly.
1) Automatic Street Light using a Single Transistor
The first circuit diagram below shows how a reasonably good automatic street lamp could be built using a single transistor, an LDR, a few resistors and a relay.
Parts List
All resistors are 1/4 watt 5% CFR
R1 = 1K
P1 = 10K preset
LDR1 = Any standard LDR
C1 = 220uF/25V electrolytic Capacitor
C2 = 10uF/25V Electrolytic Capacitor
C3 = 1000uF/25V Electrolytic Capacitor
D1----D5 = 1N4007 Diodes
T1 = BC547 Transistor
TR1 = 0-12V/500mA or 1Amp Transformer
RL1 = 12V Relay 200 to 400 ohm coil resistance
LED Bulb = LED bulb 220V/120V, 100 watt or as per street light requirement.
The working of the circuit is simple. During day time when the ambient light is sufficiently high, the LDR has a low resistance. Due to this low resistance it keeps the transistor base more towards the positive level, causing the transistor base at the required 0.6V. The transistor therefore remains switched ON.
With the transistor in the switched ON condition, the relay also remains activated with its contacts resting on the N/O position.
Since the lamp is connected at the N/C position of the relay, the lamp remains switched OFF.
Now, when the ambient light begins to fall during evening and finally reaches a level where the resistance of the LDR increases adequately, the ground potential on the transistor base is raised via the P1, cutting off the biasing potential to the base.
When this happens, the transistor is eventually switched ON. When the transistor is switched ON, its collector becomes active and it deactivates the relay. The relay contacts change from its initial N/O position to the N/C position.
This allows the current to flow through the lamp, and the lamp illuminates.
The next morning, when the ambient light level on the LDR increases, the lamp is switched off yet again, and the cycle repeats itself everyday.
The capacitors at the base of the transistor and the relay ensure that during the transition periods (twilight) or the trip points, the relay contacts do not chatter, rather changeover smoothly.
The potentiometer or the preset can be set appropriately to determine at what light levels the relay is switched ON and OFF.
Remember, while installing the street light circuit make sure the light from the bulb does not fall on the LDR, otherwise that will lead to rapid oscillations of the relay and the lamp.
How to Set up
Keep the preset wiper at the ground level.
Switch ON the power supply.
Illuminate the LDR or the premise with the required amount of light at which you want the relay changeover to happen.
Now slowly adjust the P1 preset until the relay just activates.
Seal the preset with quick-fix glue.
Your circuit is all set now.
Next, test the results by covering the LDR with an opaque shield, you will find the LED bulb switching ON instantly, and vice versa,
2) Using IC 555
Although the above transistorized is simple, its operation may not be too accurate. Meaning, the ON/OFF switching of the relay might not happen exactly at the same dawn/dusk periods.
The second design discussed below uses the IC 555 and overcomes this issue effectively.
Parts List
R1 = 220K 1/4 watt resistor or 1M preset
R2 = 1M 1/4 watt resistor
R3 = 10K 1/4 watt resistor
R4 = 100K 1/4 watt resistor
LDR1 = any standard LDR
C1 = 220uF electrolytic capacitor
D1 = 1N4007 Diode
T1 = BC547 transistor
IC1 = 555 IC
RL1 = 12V relay 200 to 400 ohm coil resistance
LED Bulb = any 100 watt LED bulb or as per the street light requirement
12V SMPS = 1no for powering the circuit
Being controlled by an internal op amp, this IC 555 based automatic street lamp circuit is extremely accurate and will consistently switch the relay everyday, almost at the identical light levels, throughout the year.
Here, the IC 555 is not used in its conventional form, rather simply used as a comparator.
The trip point can set using the indicated potentiometer or a preset R1. R1 can be a fixed 220K resistor if no precise adjustments are required, or it can be replaced with a 1M preset for precise adjustments.
How it Works
During day time when there's ample light on the LDR, the LDR resistance is low, which keeps the pin#2 to ground level causing the output pin#3 potential to be high.
This causes the relay to remain switched OFF with its contacts held at N/C. This in turn causes the light bulb to remain switched OFF.
When night sets in, the light on the LDR decreases causing its resistance to increase. This causes a positive potential to develop on pin#2 of the IC 555, via R1. Due to this pin#3 turns negative triggering ON the relay. The relay contacts now shift towards the N/O turning ON the lamp.
The 555 IC is used as a comparator in this circuit, rather than as an astable or monostable multivibrator. To understand this fairly uncommon use, it's important to understand how a 555 works in general: When input pin 2 receives a trigger (low pulse), the output rises high. This low trigger pulse is defined as a voltage that is less than 1/3 of the supply voltage. When the voltage at the second input, pin 6, temporarily exceeds 2/3 of the supply level, the output goes low again.
Although the second input pin 6 is not used in this arrangement, the chip's output could still flip to the low state since pin 6 is linked directly to the positive supply rail.
By connecting a resistor between pins 5 and 7 of the 555, as illustrated in the circuit diagram the level of hysteresis can be controlled. The level of hysteresis is inversely related to the resistor value, with 100K being a good place to start for research. If R1 is replaced with an 1M potentiometer or preset, the circuit's responsiveness could be adjusted.
Theoretically, the circuit's supply voltage has to be equal to the relay's coil voltage. Nevertheless, do not use more than 16 V since the 555 could well be damaged. At a supply voltage of 12 V, the circuit's current usage, excluding the relay, is 4 mA. The components R2 and C1 guarantee that the relay is powered after a delay of around 2 seconds, making the circuit insensitive to sudden changes in light intensity.
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