Department of Electrical Engineering
Electronics I: EEEN3421
Project
Dark Light Sensor
Team:
Student Names
Hussain Al-Marhoon 200600719
Ali XXX 200XXXXXX
Instructor: Dr. Chedly B. Yahya
Term: Fall 2012-13
1. Introduction and Application
The dark light sensor is a device that can power a light automatically in the dark. We
used the theory that we studied in the lectures of the Electronics I classes and also what
we did experimentally in the lab.
We can use the concept of this project to power the lights in
the street. As the dark falls, the lights will turns on
automatically. Also, we can use it in our houses as
emergency lights. When the electricity breakdown, the light
automatically turns on and lights the house. The importance
of the project is that it will help to save energy.
Fig. 1: Sensor Circuit
2. Components:
1. 9V supply voltage
2. BJT transistor 2N3904 (npn)
3. Wight color LED
4. Resistors 10k, potiontial meter Resistors
5. LDR (Light Dependent Resistance)
3. Circuit Operation:
The sensor used is a Light dependent resistor
(LDR), also called as Cadmium Sulphide (CdS) cell
or photoresistor is a resistor whose value depends
upon the incident light intensity. In darkness, the
resistance of LDR becomes high and in light, the
resistance gets low. The resistance variation
phenomenon of LDR has been taken as a base for
making circuits of LDR Engineering.
Fig. 2: LDR Characteristics
How it Works:
As the light is falling on the LDR (Light Dependent Resistance) the Resistance will be
low and the transistor will not conduct. So, the LED light will not power on. But, if the
light is off, and there is no light falling on the LDR, the LDR resistance will be high and
the transistor will conduct. When the transistor conduct LED light will get power to turn
on. R1 controls the sensitivity of the circuit. When R1 is high, more darkness needed to
turn on the LED light. When, R1 is low, less darkness needed to turn on the LED light.
4. Circuit Design and Test
Design: how you selected a key R value to get the desired BJT
mode or output V. How you selected the appropriate size for LDR,
a diode or …. Include any simulation.
Testing:
Include any measurements for LDR at different lights, BJT DC
voltages, …… see table
VB VC IC
Dark ??
Light
Fig. 3: Real Circuit and testing
5. Conclusion:
During the implementation of our dark light sensor project we became familiar with the
components of electronics that we studied in the course, and how we can use them in our
daily devices. We learned how to design a circuit by using the appropriate component
values to get the needed output. We also learned how to troubleshoot the circuit and make
adjustments to get it to operate as desired.