10 LED Projects for Geeks: Build Light-Up Costumes, Sci-Fi Gadgets, and Other Clever Inventions
intrO ductiOn by m attheW b ecKler Welcome to 10 LED Projects for Geeks featuring 10 projects of varying complexity that you can build using electronics You’ll be using the Raspberry Pi and Arduino to create all kinds of gadgets and inventions in this book In this introduction you’ll learn how to get started with both boards including installing the necessary software and you’ll meet the simple electronic component that is the focus of this book the LED At the end of this introduction you’ll also find a list of popular suppliers for parts you’ll need in the projects All About lEDs Before you start building cool projects using LEDs let’s take a moment to define them An LED is a circuit component that converts electricity into light LEDs come in all colors shapes and sizes and are useful in a variety of projects Most LEDs are used for indication meaning they indicate the status of something to a nearby human such as door is open radio is on or security system is armed Nowadays larger and brighter LEDs are available that can provide illumination of an object or region Figure 1 shows some basic LEDs used for indication LED stands for light-emitting diode There are a few words here to unpack but let’s start with the word diode In a circuit a diode works like a one-way valve permitting electricity to flow in only one predefined direction If you try to send electricity in the other direc tion it won’t flow Diodes convert alternating current AC electricity 2 i n t rO d u c t i O n Figure 1 A variety of single LEDs
into direct current DC a process called rectification Diodes were originally designed for use in AM radio receivers to rectify radio frequency signals but are now used in many different applications where electrical current must flow in only one direction For example diodes in many consumer electronics help protect the circuitry against batteries inserted backward Most of the time however the diode aspect of an LED is not important The rest of the name light-emitting simply means that this type of diode is designed to light up when electricity passes through How lEDs Work An LED is a semiconductor device built with crystalline metals like silicon and germanium plus small amounts of impurities that change the characteristics of the material These impurities are added to the semiconductor in a process called doping The added element called the dopant changes the base material into either a p-type or n-type semiconductor The distinction between p-type and n-type depends on whether the dopant adds excess free electrons or causes a deficit of free electrons The place where these two types of doped semiconductor meet is called the P-N junction and this is where light is created Electrical energy passing through the junction excites some of the charge carriers which emit light when they return to their nonexcited state in a process called electroluminescence The exact chemical composition of the semiconductor mate rial determines the band gap of the materials involved which in turn determines the color of light produced The first LEDs developed in the 1960s emitted light in the infrared end of the color spectrum which is invisible to the human eye but still useful for scientific experi ments Later developments of other semiconductors and dopants introduced new visible colors resulting in mass production of red LEDs in the late 1960s and yellow LEDs in the early 1970s A high-brightness blue LED was very difficult to develop and was considered the Holy Grail of the LED world until 1994 when three Japanese scientists finally figured out the secret to a blue LED They received the 2014 Nobel Prize in physics for this accomplishment 3 i n t rO d u c t i O n
A briEf History of ArtifiCiAl ligHting Throughout human history the development of artificial lighting has been incredibly important in the advancement of technology Without artificial lighting it’s almost impossible to do much produc tive work after sunset whether that involves crafting entertainment or education For a long time the only way to produce artificial light was to burn some sort of fuel such as wood beeswax oil coal gas or kerosene This changed with the development of electric ity distribution networks in the late 1800s when electric lighting became widespread Early electric lighting consisted of incandescent light bulbs which produce light by heating a thin filament wire until it glows white-hot typically in a bulb filled with inert gas to extend the fila ment life These bulbs convert only a small percentage of the input energy into light wasting the rest as heat Incandescent light bulbs eventually gave way to gas-discharge bulbs including fluorescent lights neon signs and high-intensity discharge HID lamps such as streetlights which pass an electric arc through a tube of sealed gas to produce light more efficiently Gas-discharge bulbs typically require a high voltage so they are inconvenient for portable and low-power applications With a light-emitting diode nothing gets white-hot and no gas arcs are involved just highly efficient light production lED Configurations LEDs are very popular for all types of artificial light and come in many configurations Let’s explore some of the most common types you’ll encounter single and bicolor lEDs The basic single LED configuration has two connections the anode and cathode If sufficient voltage is applied the LED lights up Pretty simple Single LEDs come in all different shapes sizes and colors and some such as the second and fourth ones shown in Figure 1 have extra plastic to help direct the generated light through an open ing in the side of an electronics case 4 i n t rO d u c t i O n
