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DARK DETECTING CIRCUITUSING
LIGHT DEPENDENT REGISTORBY
ADITI VERMAX-B
RYAN INTERNATIONAL SCHOOLNOIDA
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1.0 Objective
Here’s a simple problem: “How do you make an LED turn on when it gets dark?” You might call it the “nightlight problem,” but the same sort of question comes up in a lot of familiar situations– emergency
lights, street lights, silly computer keyboard backlights, an electronic letter box,Escalator automatice on /off,Matro To-ken entry gate, Automatic door open/close system,faucets
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SIMPLE AND ECONOMICAL DARK-DETECTING CIRCUIT USING
LIGHT DEPENDENT REGISTOR(LDR)
1.1Problem
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�ଁhe circuit with with a CdS(cadmium sulphide) pho-toresistor, sometimes called a photocell or LDR, for “light-de¬pendent resistor.” Photoresistors are re-
liable and cost about Rs 50 each. The LDR based circuits can be further enhanced to provide solution to the Prob-lem described in paragraph 1.1 1 2
for your kitchen and bathroom, LDR is also EPA Water Senser and the list goes on.
1.2 Solutions
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2.0 ĦOW LIGHT DEPEND-ENT RESISTOR ( LDR) WORKS
Łight dependent resistor (LDR) is resistor whose resistance varies with light intensity. This resistor uses a high resistance conductor, whereby, light energy contained in the light makes the electrons
to move changing the resistive property of the semicon-ductor. Depending on the semiconductor, the resistance may either increase or decrease.
LDR is an abbreviation for light dependent resistor. The LDR is made of a semiconductor material. As light falls on the high resistance semiconductor, the light photons are absorbed by the semiconductor lattice. Some of their
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energy is transferred to the electrons. Some of the electrons conduct electricity as they gain sufficient energy to break free from the crystal lattice. As a result, the semiconductor resistance and hence the overall LDR resistance lowers. LDR is a very useful component used for a variety of light sensing applications around us.
3.0 ÇOMPONENTS USED
i. 9v Battery with strip ii. Switch iii. L.D.R (Light Depending Resistance) iv. BC 547 Transistorv. L.E.D (Light Emitting Diode)
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vi. Resistance of 100 Kilo ohms,100 ohms vii. P.C.B (Printed Circuit Board )
3.1 Description of Components
a) Battery: For 9v power supply we can use 6pcs dry cell or 6F22 9v single piece battery
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+-
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b)Switch:Any general purpose switch can be used. Switch is used as circuit breaker.
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c) L.D.R: (Light Dependent Re-sistance) or Photoresistor : It is a special type of resistance whose value depends on the brightness of light which is falling on it. It has resistance of about 1mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum. A photore-sistor or light dependent resistor (LDR)
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is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits photoconductiv-ity. Photoelectric or light sensing device are used in almost any branch of industry for control, safety, amusement and sound reproduction and inspection and meas-urement.
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d) L.E.D: (Light Emitting Diode): A diode is a component that only allows elec-tricity to flow one way. It can be thought as a sort of one way street for electrons. Because of this characteristic, diode are used to trans-form or rectify AC voltage into a DC volt-age. Diodes have two connections, an anode and a cathode. The cathode is the end on the schematic with the point of the triangle pointing towards a line. In other words, the triangle points toward that cathode. The an-
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ode is, of course, the opposite end. Current flows from the anode to the cathode. Light emitting diodes, or LEDs, differ from regu-lar diodes in that when a voltage is applied, they emit light. This light can be red (most common), green, yellow, orange, blue (not very common), or infa red. LEDs are used as indicators, transmitters, etc. Most likely, a LED will never burn out like a regular lamp will and requires many times less cur¬rent. Because LEDs act like regular diodes and
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will form a short if connected between + and -, a current limiting resistor is used to pre-vent that very thing. LEDs may or may not be drawn with the circle surrounding them.
-+
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e) Resistance: Resistors are one of the most common electronic components. A resistor is a device that limits, or resists cur-rent. The current limiting ability or resist-ance is measured in ohms, represented by the Greek symbol Omega. Variable resistors (also called potentiometers or just “pots”) are resistors that have a variable resistance. You adjust the resistance by turning a shaft. This shaft moves a wiper across the actual resis-tor element. By changing the amounts of re-
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sistor between the wiper connection and the connection (s) to the resistor element, you can change the resistance.
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You will often see the resistance of resistors written with K (kilo ohms) after the number value. This means that there are that many thousands of ohms. For example, 1K is 1000 ohm,2K is 2000 ohm, 3.3K is 3300 ohm, etc. You may also see the suffix M (mega ohms). This simply means million. Resistors are also rated by their power handling capabil-ity. This is the amount of heat the resistor can take be¬fore it is destroyed. The power capability is measured in W (watts) Com-
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mon wattages for variable resistors are 1/8W, 1/4W, 1/2W and 1W. Anything of a higher wattage is referred to as a rheostat.f ) PCB (Printed Circuit Board) : With the help of P.C.B it is easy to assem-ble circuit with neat and clean end products. P.C.B is made of Bakelite with surface pasted with copper track-layout. For each compo-nents leg, hole is made. Connection pin is passed through the hole and is soldered.
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g) Transistor : A transistor is a semi-conductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current ap-plied to one pair of the transistor’s terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a
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signal. Today, some transistors are packaged individually, but many more are found em-bedded in integrated circuits. The transistor is the fundamental building block of mod-ern electronic devices, and is ubiquitous in modern electronic systems.
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5.0 CIRCUIT DESCRIPTION OF DARK-DETECTING CIR-
CUIT LDR CIRCUIT
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• It is a simple and powerful concept,which uses transistor (BC 547 NPN) as a SWITCH to ON and OFF the LED auto-matically.
• It automatically switches ON LEDwhen the sunlight goes below the vis-ible region of our eyes. (e.g in evening af-
5.0 ŴORKING ØF ŦHE ÇIRCUIT
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ter Sunset). In this case as the light goes down, the LDR Resistance increases and then the circuit automatically switches the LED(ON)
• It automatically switches OFF LEDwhen Sunlight fall on it ( i.e on LDR ) e.g in morning, by using a sensor called LDR (Light Dependent Resistor) which senses
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the light just like our eyes. In this case as the light increases, the LDR Resistance de-creases and then the circuit automatically switches the LED(OFF)
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6.0 OBSERVATIONS
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7.0 INDUSTRIAL APPLICATION OF LIGHT/DARK DETECTING LDR CIR-CUIT
7.1 Automatic Street Light Control7.2 Camera Exposure Control7.3 Photocopy Machines - density of toner7.4 Densitometer7.5 Automated Rear View Mirror7.6 Automatic Headlight Dimmer7.7 Night Light Control7.8 Oil Burner Flame Out
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7.9 Colorimetric Test Equipment
8.0 PRECAUTIONS
a) Use a Sensitive LDR. Before using it should be tested with multimeter.
b) Transistor should not be heated too much while soldering. This can destroy the transistor.
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c) Opposite polarity of battery can destroy I.C so please check the polarity before switching ON the circuit. One should use diode in series with switch for safety since diode allows flowing current in one direc-tion only.
d) L.E.D glows in forward bias only so in-correct polarity of L.E.D will not glow.
e) Each component should be soldered neat 31
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and clean. We should check for any dry sol-dered.
f) LDR should be so adjusted that it should not get light itself.
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Thank You
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