1. Faculty of engineering – Shoubra
Benha University
Report .
Department Communications & Electronics
Academic Year 2022-2023 3rd
Year
Course name electronic circuits
Title: -
Automatic Night Light
By:
Name Edu mail
1 علي الشربيني عماد احمد ahmed195103@feng.bu.edu.eg
2 قطب حسن احمد Ahmed195048@feng.bu.edu.eg
3 لطفي الناصر عبد احمد Ahmed195096@feng.bu.edu.eg
Video link: https://drive.google.com/drive/u/0/folders/1OwxN-
0uAlst87JVm48gmxDSLcQRMcrRt
Approved by:
Examiners committee Signature
Dr. Sawsan Abd-Ellatif
2. Benha University
Faculty of Engineering - Shoubra
Academic year 2022- 2023
Component of circuit:
• BC547 Transistor : 2
• RED-LED : 1
• Battery 9V : 1
• LDR : 1
• 100 ohm Resistor : 1
• 47 kohm resistor : 1
• 1 kohm resistor : 1
• Breadboard
• Wires
Applications:
1. This project can be implemented in applications like automatic switching on
of lights when it becomes dark (at night).
2. This circuit can be part of a bigger circuit or project like home automation or
home security system.
3. Automatic lights control system in industry
3. Benha University
Faculty of Engineering - Shoubra
Academic year 2022- 2023
In some cities and villages, sometimes street lights glow in day time without any reason. In
mining regions people face many difficulties due to absence of light in the nights. In frontier
and hilly areas, people face many problems due to damaged street lights. For solving these
problems, we create a device in which the lights glow in night and in day time, they get
switched off automatically and don't glow. Due to use of it, we can solve above problems and
can also save electricity.
An LDR or light dependent resistor is also known as photo resistor,
photocell , photoconductor. It is a one type of resistor whose resistance
varies depending on the amount of light falling on its surface.These
resistors have a variety of functions and resistance. For instance,
when the LDR is in darkness, then it can be used to turn ON a light or
to turn OFF a light when it is in the light. A typical light dependent
resistor has a resistance in the darkness of 1MOhm, and in the
brightness a resistance of a couple of KOhm.
BC547 Transistor: is an NPN transistor. A small current of the base
terminal of this transistor will control the large current of emitter and base
terminals. The main function of this transistor is to amplify as well as
switching purposes. The maximum gain current of this transistor is 800A.
Physical operation : We know that the resistance of the LDR inversely proportional to light
intensity. And we also know that the light intensity from the LED is directly proportional to the
current flow through it. Here we discuss the two cases of the sensor.
4. Benha University
Faculty of Engineering - Shoubra
Academic year 2022- 2023
Csase I: If light on the LDR increase, then the resistance of the LDR decrease, then the base
voltage decrease, then the emitter and collector current decrease, then the light intensity from the
LED decrease.
Case II: If the light on LDR decrease, then the resistance of the LDR increase, then the base
voltage increase, then emitter and collector current increase, then the light intensity from the LED
increase.
Working steps:
• Connect emitter of (Q1) to the ground.
• Connect base of (Q1) to resistor (4.7KΩ) then connect another part of resistor to the ground.
• Connect base of (Q1) to LDR then connect another part of that to power(9V).
• Connect collector of (Q1) to resistor (1KΩ) then connect another part to power(9V).
• Connect collector of (Q1) to base of (Q2) then connect emitter of (Q2) to ground.
• Connect collector of (Q2) to cathode of the LED then connect anode of that to resistor
(100Ω) then connect another part of that to ground.
• Connect negative part of battery (9V) to ground of breadboard then connect positive part of
that to the power of breadboard.
5. Benha University
Faculty of Engineering - Shoubra
Academic year 2022- 2023
Circuit diagram :
• OFF state:
LDR expose to high light (Lightness)
Resistance of LDR will be decreased so VBE
will increase, transistor (Q1) will be on so
VCB = 0.2 and VBE of transistor (Q2) will less
than 0.7, Q2 will be off and LED will turn off.
• ON state:
LDR expose to low light (Darkness)
Resistance of LDR will be increased so VBE
will decrease, transistor (Q1) will be off and VC will be maximum equal to VCC so
VBE of transistor (Q2) will equal to 0.7, Q2 will be on and
LED will turn on.
Simulation:
• Darkness (at Night) → LED ON
• Lightness (at morning)→ LED OFF
