Chapter 3. Project 2 – Remote Controlled TV Backlight

In the previous chapter, Project 1 – LED Night Lamp, we dived into the amazing world of LEDs. We created some cool projects using different types of LEDs. Now, we will use another type of LED – an IR (Infrared) LED. In this chapter, we will start by learning the basics of IR LEDs and the basics of IR communication. Once you have learned about programming the IR sensor, we will use it to control a TV backlight using a remote. In this chapter, you will learn about the following:

• Introduction to and the workings of an IR LED

• Programming an IR sensor

• How to control an LED array

• Developing a remote controlled TV backlight

Introduction to IR LEDs

In the world of wireless technology, IR (infrared) is one of the most common, inexpensive, and easy to use modes of communication. You might have always wondered how a TV remote works. A TV remote uses IR LEDs to send out the signal. As the wavelength of light emitted from the IR LED is longer than the visible light, one can't see it with the naked eye. But, if you look through the camera of your mobile or any other camera, you can see the light beaming when you press any key on the remote. Let's first understand what an IR LED is and what the different applications of an IR LED are.

What is IR LED?

An IR (infrared) LED, also known as an IR (infrared) transmitter, transmits infrared waves in the range of 875 nm to 950 nm. Usually, IR LEDs are made up of gallium arsenide or aluminum gallium arsenide. The working principle of an IR LED is the same as we mentioned in the previous chapters. The longer lead of the LED is the anode and the shorter one is the cathode, as shown...

IR sensors

We have learned the basics of IR communication and IR LEDs, so now we will move on to making our own IR sensor.

There are various types of IR sensors, depending upon the application. Proximity sensors, obstruction sensors, and contrast sensors (used in line follower robot) are a few examples which use IR sensors.

Working mechanism

An IR sensor consists of an IR LED (which works as a transmitter) and a photodiode (which works as a receiver) pair. The IR LED emits IR radiation, which, on receiving at the photodiode dictates the output of the sensor.

There are different types of use cases for an IR sensor. For example, if we held an IR LED directly in front of the photodiode, such that almost all the radiation reaches the photodiode, this can be used as burglar alarm. So, when anyone interrupts the line of sight between the IR LED and the photodiode, this will break the continuous radiation coming from the IR LED, and we can program it to raise an alarm. This type of mechanism is also...

LED strips

LED strips are flexible circuit boards with full color LEDs soldered on them. There are two basic types of LED strip: the "analog" and "digital" kinds. Analog strips have all the LEDs connected in parallel. So, they act as one huge tri-color LED. In case of an analog LED strip, we can't set the color/brightness of each LED. So, they are easy to use and inexpensive. Digital LED strips work in a different way. To use the LED, we have to send digital code corresponding to each LED in the case of a digital LED strip. As they provide more modularity, they are quite expensive. Also, digital LED strips are difficult to use compared to analog LED strips:

Internally, RGB LEDs are connected to each other in parallel. One section of the strip contains all three LEDs, connected in parallel. A complete LED strip is made up of a number of parallel RGB LEDs connected in series. Connection in one block/section is as shown in the following figure:

As one section contains multiple LEDs, it requires...

Summary

In this chapter, we started with the basics of IR LEDs and IR communication. After that, we learnt about programming IR sensors and their applications. By the end of this chapter, we learnt about controlling an LED strip, and we completed our chapter by developing a remote controlled TV backlight.

In the coming chapters, we will start into the more advanced stuff of developing an LED cube, sound visualization, and persistence of vision.