project report of dark sensor using photo diode or automatic street light

1. Dhananjaysinh Jhala
Computerengineering
170410107027
Aim: To make working modelon the topic “dark sensorusing photodiode”
Apparatus:
1. Breadboard
 It is a device for testing temporary electronic projects.
 It has tiny sockets or holes arranged on a grid
2. Two 330 ohm resistors
3. 1k Ω resistor, 4.7k Ω resistor
4. 1 led
 A light-emitting diode (LED) is a two-lead semiconductor light
source.
 It is a p–n junction diode that emits light when activated. When
a suitable voltage is applied to the leads, electrons are able to
recombine with electronholes within the device, releasing
energy in the form of photons.
5. BC 547 transistor
 A transistor is a semiconductordevice used to amplify or switch
electronic signals and electrical power.
 BC547 is an NPN bi-polar junction transistor. BC547 is mainly
used for amplification and switching purposes.

2. 6. Photodiode
 Photodiode is in the class of photo junction device which is
basically a PN junction light sensor.
 When light is incident on a Photodiode,the electrons and holes
are separated and will allow the junction to conduct.
Major componentused:
 Photodiode is the major componentused in the project
o A photodiodeis a semiconductordevice that converts light into
an electrical current.
o The current is generated when photons are absorbed in the
photodiode.
o Photodiodesusually have a slower response time as their
surface area increases.
o Many diodes designed foruse specificallyas a photodiode use
a PIN junction rather than a p–n junction, to increase the speed
of response.
o Dark current is the current through the photodiodein the
absence of light, when it is operated in photoconductive mode.

3. o The dark current includes photocurrent generated by
background radiation and the saturation current of the
semiconductorjunction.
o The photodiode used in this circuit is photodarlington.
o The SDP8105 is an NPN silicon photodarlington transfer
molded in a T-1 black plastic package to minimize effectof
visible ambient light.
Working:
 In the circuit for the project“dark sensorusing photodiode” a 9 V
battery is connected to the circuit consisting of 2 BC547 transistors, 1
photodiode,LED and suitable values of resistances.
 Anode of photodiodeis to be connected to baseof transistor.
 It uses a simple and powerful concept,which uses transistor (BC
547 NPN) as a switch to switch ON and OFF the LED automatically.
 As we all know a photodiode produces photocurrentby generating
electron-hole pairs, due to the absorption of light in the intrinsic or
depletionregion.
 The photocurrent thus generated is proportional to the absorbed
light intensity.
 Now when the circuit is connected to a power supply, a 9 V battery in
our case and in the case of dark conditions,dark currents are
produced in the photodiode usedin the circuit
 Dark currents are due to the random generation
of electrons and holes within the depletionregion of the device.
 The dark current includes photocurrent generated by background
radiation and the saturation current of the semiconductorjunction.
 Thus when there is absence of light which itself is darkness then the
photocurrents developed in the photodiodeturn on the second
transistor and currents flows through the LED and there is light
glowing inside the LED and thus darkness is successfully sensed.
 While in the condition of light, the photodiode does notinduce the
second transistor to turn on thus LED does not glow and thus LED is
shut off when there is light.

4.  This circuit is very crucial in daily life also such as in automatic street
light systems
 Therefore during night time or when it is dark the street light
automatically turns ON and when there is light or daytime there is
street light automatically turns OFF.
 This can help save energy as well as reduce the effortin street light
management and save time as well.
Circuitdiagram:

5. Conclusion/Result:
Thus a circuit that can sense darkness and automatically turn on and off
light source i.e. dark sensor using photodiode is made.