Light Dependent Resistors Circuit Diagram

LDRs or lightweight Dependent Resistors are terribly helpful particularly in light/dark sensor circuits. Normally the resistance of an LDR is incredibly high, typically as high as a thousand 000 ohms, however once they are illuminated with lightweight resistance drops dramatically.

 The animation opposite shows that when the torch is turned on, the resistance of the LDR falls, permitting current to have it.Circuit Wizard software has been used to show, the vary of values of a ORP12, LDR .
When a light-weight level of a thousand lux (bright light) is directed towards it, the resistance is 400R (ohms).

When a light-weight level of ten lux (very low light level) is directed towards it, the resistance has risen dramatically to ten.43M (10430000 ohms).

This is an example of a light-weight sensor circuit :

When the sunshine level is low the resistance of the LDR is high. This prevents current from flowing to the bottom of the transistors. Consequently the LED doesn't lightweight. However, when lightweight shines onto the LDR its resistance falls and current flows into the bottom of the primary transistor and then the second transistor. The LED lights.

The preset resistor will be turned up or right down to increase or decrease resistance, during this means it will build the circuit additional or less sensitive.

Source by : Streampowers

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Morning Alarm Circuit Diagram Using LDR

Description

 Circuit showing a morning alarm.Here we have used a switching transistor.When the sun rise up ldr is low resistance so the ldr is conduct and a positive volt coming to the base of the Q1 there for the transistor will switch.This time  the buzzer is ON . Adjust the preset control the intensity of light.Manually cut off the power.Are you interested please comment and join this site


Component Required

                Resistor  4.7k preset  , LDR

                Transistor   BC 548

                Buzzer

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Dark Sensitive Power Switch Circuit Diagram Using LDR

Description

Circuit showing a Dark Sensitive Power Switch .Here we have used a ldr and a ordinary transistor for making this circuit


.Connect any 230 volt equipment at the load .You need a 9 volt power supply
Components Required

         Resistor

                     10 k , 680 R

          Transistor

                        BC 548

          Diode

                   IN 4007

         Relay

         LDR

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Morning Alarm Circuit Diagram based LDR

This LDR based alarm can be used as get up alarm. The Alarm turns on in the morning automatically and turns off only when manually switched off ,so you will have to get up. It is a simple LDR based light sensor circuit.

Morning Alarm Circuit Diagram based LDR
 

LDR or Light Dependent Resistor is a kind of variable resistor and its resistance depends on the intensity of light falling on it. In complete dark, its resistance is as high as 1 Meg Ohm, but it reduces to 100 ohms or less in full light. So it is an ideal device to use as light switch. Sensitivity of LDR depends on its size also. Commonly available sizes are 3mm, 5mm, 10mm etc. But costly types with greater sensitivity are also available.

When the circuit is place in dark, near the window, LDR fails to conduct and T1 will not get base bias. So it remains off and buzzer will be silent. When the sunlight falls on LDR, IN the morning, LDR conducts and provides base bias to T1. T1 then conducts to activate the buzzer. Capacitor C1 is provided for the clean switching of T1. T1 will conduct only when C1 is charged fully. This prevents chirping sound during light transition.You can use an easily available Music buzzer to get melody tone.

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Optical Theremin Circuit Diagram

Normally, Theremin works by detecting hand proximity using capacitive coupling method. A Theremin circuit shown in the schematic diagram below use different method to control the pitch. The oscillator of this tone generator, both the volume and frequency  are controlled using LDRs, a light sensitive electronic component, so we can call this circuit an optical Theremin.  Look at the following schematic diagram.

 Simple Optical Theremin Circuit Diagram

LDR1 control the frequency of this Theremin, while LDR2 control the volume level. We can place the LDR in two boxes where we can use our hand to control the aperture of the box, allowing smooth control of light amount that expose the LDR. 

This light is expected to come from ambient light, entering the box through the hand controlled aperture. This optical Theremin assume a stable ambient light to produce smooth control. The output will be heard on a small loudspeaker, but will be in very low volume. You can just amplify this output with a standard audio power amplifier to get better loudness.

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