Light Intensity Measurement Using Ldr

Light Intensity Measurement Using Ldr – Optical sensors are often used in electronic applications. The most common is the photoresistor or light-dependent resistor. Despite the long response time, this sensor is cheap and useful in many applications.

A photoresistor consists of a zigzag track of light-sensitive semiconductors. It depends on ambient light, but provides pure resistance. If in the dark The sensor has a high resistance — think several thousand ohms or megohms. In light, the resistance of the sensor drops to a few hundred ohms.

Light Intensity Measurement Using Ldr

Practically, Light Dependent Resistors (LDRs) are poor at measuring light intensity. The LDR’s response to light greatly reduces resistance. In addition, its spectral response is tuned to light’s maximum wavelength of 540 nm.

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However, adjusting this green light makes it extra sensitive to light visible to the human eye. An LDR can normally measure light or dark due to its specially tuned spectral response.

A light or dark sensor can be designed by using an LDR connected to a voltage divider circuit.

The output signal from the voltage divider network is analog. A voltage divider can be connected to an operational amplifier to design an ideal light or dark sensor. First, connect the output of the LDR resistor voltage divider to the non-inverting input of the OPAMP. Apply the reference voltage to the inverting input.

Then try connecting the output of the LDR resistor voltage divider to the inverting input of an OPAMP. Apply a reference voltage to the non-inverting input.

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The reference voltage can be adjusted with a pot or a variable resistor. Regardless of which way the OP-AMP and the voltage divider network are connected, the output logic can be used to make a light or dark sensor.

This example uses the LM358 dual op amp IC. According to the above circuit, the output of the LDR resistor network is connected to the non-inverting input of one of the op-amps and the inverting input of the other LM358 op-amp.

The reference voltage can be adjusted by a variable resistor connected to the inverting input of the first op-amp and the non-inverting input of the second. The output of the two op-amps will operate in opposite ways in light or dark conditions. The output signal from one of the op-amps is taken via jumper heads. The user can choose to use the circuit as a light or dark sensor.

Connecting the LDR to the Arduino The photoresistor can be connected to the Arduino with a digital or analog input. If the voltage divider LDR is connected directly to the Arduino (or any microcontroller), the output of the voltage divider network must be connected to the analog input of the Arduino.

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In this case, an Arduino can be programmed to read an analog voltage from the LDR resistor network and compare it to a reference value to make a decision — like automatically turning electronic lights on or off when it’s dark. Turns on automatically when light is detected.

A second way to approach this is to pair the LDR resistor network with an operational amplifier (op-amp) and feed the output of the op-amp as a digital input to the Arduino.

In this method, the output of the op-amp is physically adjusted through a potentiometer or variable resistor. This means that the user does not have to reprogram the Arduino to recalibrate the sensor when or if needed. He or she can simply adjust the pot and the recalibration is complete.

Here, the Arduino reads the digital logic from the LDR op-amp circuit and performs the decision making. This method is easy to connect Arduino and LDR; Easy to use and usually more preferred.

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For this project, Let’s attach an LDR sensor to detect light or dark by placing jumpers. We will use this module to monitor the output of LDR op-amp sensor module using Arduino Serial Monitor.

Circuit Connections Begin by connecting the LDR to the 10K resistor in the voltage divider network. Connect the LDR side of the network to 5V DC and the resistor side of the network to ground (since the voltage drop must occur across the LDR).

Then connect the output of the LDR resistor network to pins 3 and 6 of the LM358 IC. Take a pot and connect its designated terminals to 5V DC and ground. Connect the pot’s variable gate to pins 2 and 5 of the LM358 IC. Pins 8 and 4 of the LM358 IC should be connected to VCC and ground.

To make the circuit work as a light sensor; Connect pin 1 of the LM358 to a digital I/O pin of the Arduino. The circuit will display HIGH when light is detected and LOW when dark.

Schematic Drawing Of The Three Different Positions That Light Intensity…

To use a dark sensor instead; Connect the LM358’s pin 7 to one of the Arduino’s digital I/O pins. As a dark sensor, the circuit is HIGH when it is dark and LOW when it is light.

The output of the LDR op-amp circuit can be used to drive the LED directly or via the Arduino.

In this lesson, Using a jumper connector or a 2-pole shunt, the circuit is taken on a circuit board where the function of light or dark sensor can be selected. An LED is already on the circuit board to indicate light or dark detection.

Therefore, the output of the LDR op-amp circuit is connected to the A0 analog input pin to monitor the change in the output voltage of the op-amp depending on whether it is light or dark.

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How the circuit works The output of the LDR resistor network is connected to the non-inverting input of one of the op-amps and the inverting input of the other LM358 op-amp. The same reference voltage is applied to the opposite inputs of both op-amps. This reference voltage is adjusted by the user.

If it is dark, LDR has high resistance in the circuit. Due to high resistance, there is a high voltage drop across it. As a result, a voltage lower than the reference voltage is output from the voltage divider network. This also means that the output on pin 1 of the LM358 is low while pin 7 is high.

When there is light The resistance of the LDR drops to a few hundred ohms. The voltage drop across the LDR is low due to the resistance drop. As a result, a voltage greater than the reference voltage is output from the voltage divider network. Therefore, the output at pin 1 of LM358 is high while pin 7 is low. In this project we will connect LDR to ATMEGA8 microcontroller, With this you can measure the light intensity in an area. In ATMEGA8 we will use 10bit ADC (Analog to Digital Conversion) function to measure the light intensity.

Am LDR is a sensor that changes its resistance when light falls on its surface. The LDR sensor comes in different sizes and shapes.

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LDRs are made of semiconductor materials to achieve their light-sensitive properties. There are many types of materials used, but the most popular is CADMIUM SULFIDE (CdS). These LDR’s or photo-RESISTORS work on the principle of “Photoconductivity”. Now this principle says that when light falls on the surface of the LDR (in this case) the conductivity of the element increases or in other words the resistance of the LDR decreases when light falls on the surface of the LDR. This resistance drop property of LDR is achieved due to the semiconductor material used on the surface. LDRs are used many times to detect the presence of light or to measure the intensity of light.

As shown in the figure above, there are different types of LDRs and each has different specifications. Typically 1MΩ-2MΩ in total darkness in LDR; 10-20KΩ at 10 LUX; 100 LUX has 2-5KΩ. The LUX graph of an LDR with typical resistance is shown in Fig.

As shown in the image above. The resistance between the two contacts of the sensor decreases when the light intensity or the current between the two contacts of the sensor increases.

Now to change the voltage to change this change in resistance, we will use a voltage divider circuit. In this resistor network we have a constant resistor and another variable resistor. As shown in Fig. Here R1 is a constant resistor and R2 is a FORCE sensor that acts as a resistor.

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The center point of the branch is measured. When the resistor R2 changes; Vout changes linearly with it. So we have a weight and a variable tension.

Now the important thing to note here is that; The input taken by the regulator for ADC conversion is less than 50 µAmp. The voltage divider load effect based on resistance is important because the current drawn from Vout of the voltage divider increases the error percentage.

What we are going to do here is take two resistors and form a divider circuit to get 5Volt Vout for a 25Volt Vin. So what we need to do is multiply the Vout value in the program by “5”.

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