A Light Dependent Resistor (aka LDR, photoconductor, or photocell) is a device which has a resistance which varies according to the amount of light falling on its surface.
An LDR and a normal resistor wired in series across a voltage, say 5V DC, can be used to develop a signal. Depending on which is tied to the 5V and which to 0V, the voltage at the point between them, call it the sensor node, will either rise or fall with increasing light. If the LDR is the component tied directly to the 5V, the sensor node will increase in voltage with increasing light. It doesn't really matter which way (rise or fall) because the designer has a choice of several simple circuits to invert the signal as needed for whatever function is to be performed.
This voltage at the sensor node (between the components) will vary gradually with the light level. To use for security light control, it's desired to develop a signal that switches level from one extreme to the other suddenly as light level goes from light to darker and darker. This result could be called a binary signal, a signal with two states (perhaps about 4V and 0.5V), indicating yes/no or 1/0. To develop this, the sensor node voltage can be compared, by an electronic circuit, with some threshold voltage to determine whether the light level is more or less than the threshold. The result of the comparison would give a "DARK? yes/no" determination.
Applications
Photoconductive cells are used in many different types of circuits and
applications.
Analog Applications
Camera Exposure Control
Auto Slide Focus - dual cell
Photocopy Machines - density of toner
Colorimetric Test Equipment
Densitometer
Electronic Scales - dual cell
Automatic Gain Control – modulated light
source
Automated Rear View Mirror
Digital Applications
Automatic Headlight Dimmer
Night Light Control
Oil Burner Flame Out
Street Light Control
Absence / Presence (beam breaker)
Position Sensor
Formula:
This formula is responsible for calculating the output power of LDR
Symbol for LDR
Light sensor circuit
Opposite is a simple light/ dark sensor. This can be connected as an input or switch to another circuit. The sensors has three green wires (1, 2 and 3). Wire 2 should always be connected to one of the inputs. If wire 1 is also connected then the sensor acts as a dark sensor. If wires 2 and 3 are connected to the inputs then sensor operates as a light sensor.
Functions of LDR...
An LDR and a normal resistor wired in series across a voltage, say 5V DC, can be used to develop a signal. Depending on which is tied to the 5V and which to 0V, the voltage at the point between them, call it the sensor node, will either rise or fall with increasing light. If the LDR is the component tied directly to the 5V, the sensor node will increase in voltage with increasing light. It doesn't really matter which way (rise or fall) because the designer has a choice of several simple circuits to invert the signal as needed for whatever function is to be performed.
This voltage at the sensor node (between the components) will vary gradually with the light level. To use for security light control, it's desired to develop a signal that switches level from one extreme to the other suddenly as light level goes from light to darker and darker. This result could be called a binary signal, a signal with two states (perhaps about 4V and 0.5V), indicating yes/no or 1/0. To develop this, the sensor node voltage can be compared, by an electronic circuit, with some threshold voltage to determine whether the light level is more or less than the threshold. The result of the comparison would give a "DARK? yes/no" determination.
Working of LDR:-
Applications
Photoconductive cells are used in many different types of circuits and
applications.
Analog Applications
Camera Exposure Control
Auto Slide Focus - dual cell
Photocopy Machines - density of toner
Colorimetric Test Equipment
Densitometer
Electronic Scales - dual cell
Automatic Gain Control – modulated light
source
Automated Rear View Mirror
Digital Applications
Automatic Headlight Dimmer
Night Light Control
Oil Burner Flame Out
Street Light Control
Absence / Presence (beam breaker)
Position Sensor
Formula:
This formula is responsible for calculating the output power of LDR
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