Video working with LDR and P IR sensors. In this video we will learn about the working principle behind popular sensors like LDR NPR. Later, we will learn how to interface them to the Raspberry Pi and create some simple projects. An LDR also known as a light dependent resistor, is a passive electronic component, basically, a resistor that has a resistance that varies depending on the light intensity. So how does an LDR work? It has two wire leads which terminate in the face of the light detector.

At the two metal dots you'll see on its face. The main body of the light detector component is made of an insulator called ceramic on the face of the ceramic attend strip of cadmium sulfide is coated on a zigzag pattern to maximize the length of this trip, while keeping the components small, this is connected at each end to an electrode. The front face is then coated in clear plastic epoxy glass are similar for protection. cadmium sulfide is a photo conductive material, which means that photons of light hitting it with sufficient energy will release electrons from their atomic bonds. The higher the light intensity, the more photons of light are hitting the cadmium sulphide strip, the more electrons are freed, the more electricity can flow through the light detector. This is the working principle of an LDR.

If we want to use analog sensors like the LDR with the Raspberry Pi four, we would need to be able to measure the resistance of the sensor. Unlike the Arduino, the Raspberry Pi's GPIO pins are unable to measure resistance and can only sense is the voltage source Apply to them is about two volts. To overcome this issue, you could use an analog to digital converter that is ADC or you could use a relatively cheap capacitor instead. Yeah, we will be using a one micro farad electrolytic capacitor. We will build a simple project using an LDR and an LED. When the LDR detects that it has duck, the LED should beyond does.

Let's continue from our last circuit. You just have to remote any extra LED. Only the red LED connected to the GPIO 17 shall remain. Now fixed TLDR on the breadboard in such a way that one of its legs is connected to a three volts pin on the PI. Just like a resistor LDR doesn't have any polarity that you can use any legs. Next, take the one micro farad electrode capacitor and fix the longer leg or the positive leg to the other leg of the LDR.

The negative leg of the capacitor should go to the ground. Finally, connect a jumper from the junction point between the LDR and the capacitor and wire it up to the GPIO 18 pin. You can find the circuit diagram in the resources. In the Tawny ID open the LDR led dot p y script from the repository and run the script. Now you block the face of the LDR and you can see that the LED is on. There are three key differences in the code as opposed to the button led dot p y code.

One is that we have imported the light sensor class from the GPIO zero library. The second is the input arguments of the class when the object is created. The first one is obviously the GPIO pin. The second is the threshold Which can be set from zero to one. Basically, the Pisces the LDR values as floating numbers from anywhere between zero to one. Yeah, if the average of the LDR values within a default time limit is about 0.2, then it's detected as light.

If it's below, it's detected as dark. The detection part comes with the light underscore detected method, which is used in a conditional branching kept inside an infinite loop to detect and respond. Please check out the resources section to find all the methods available for the light sensor class. Now, let us look at the PIR sensor. The term p AR is the short form for passive infrared. The term passive indicates that the sensor does not emit the reffered ir signals itself, rather, passively detects the infrared radiation Coming from the human body in the surrounding area.

P AR are basically made up of a piezo electric sensor and a Fresnel lens. The Pyro electric sensor in a motion detector is actually split into two halves, the two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low. So, when a human body or any animal passes by, it intercepts one slot of the PIR sensor. This causes a positive differential change in between the two halves. When the subject leaves the sensing area, the sensor generates a negative differential change between the two halves.

The Fresnel lens is used, so that the two halves of the sensor can detect motion from longer distances. Next, we will interface the PIR sensor and detect Motion. The PIR sensor is a self contained sensor, with all the necessary circuitry inbuilt on the PCB. Thus, we need to wire it up directly. A p IR sensor will have three pins for interfacing Vcc ground and D out. D out means digital out.

Unlike the LDR sensor, pay our sensor will only written either as one or zero as the pins of the PIR sensor, our main data types, we need a female to female jumper cables to interface First, connect the VCC pin to a three v three pin on the PI. Next connect the ground pin to any of the ground pins of the PI. Finally, connect the D or pen to GPIO pin four of the PI now open the P AR led dot p by code in Tony Ida and run the script, move your hand in front of the P IR sensor. And you can see the LED lighting up. The code is almost similar to the LDR led dot p y code. The only difference is that we have imported the motion sensor class, used it to create an object name, VR, and finally detected the motion with the motion underscore detected method.

We have added a half second delay to avoid the LED to flicker on false positive detections summary. In this video we have covered the following working principle of an LDR interfacing of an LDR with the PI working principle of a PR interfacing of a PR with the PI. In the next video, we will learn to interface and work with relays