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Wednesday, October 29, 2014

On 4:05 PM by Richard St-Pierre


Overview

This tutorial is a very simple introduction to some common components used in electronic circuits.
It is intended to help with component identification and understanding the basic functions of these devices. As with many things, the more you learn, the more questions you're likely to have, so feel free to explore our other tutorials and ask any questions here in the comments.

We've found it's sometimes helpful to use analogies to help visualize new concepts. Throughout this walkthrough we'll use water to explain the meaning terms and the electrical behavior of some of these devices.

Voltage

The voltage of a circuit is the 'pressure' that pushes the electrons around. You can think of it as the pressure from a faucet or garden hose. Voltage is measured in Volts.

Current

Current is the measure of the amount of electrons flowing through a circuit. You can think of it as the amount of water coming out of a garden hose. Current is measured in Amperes. Current flows when a complete circuit is formed. To complete a circuit, a return path to the energy source (often referred to as ground or GND for short) is required.

Electronic Components

Here is a short list of some of the common electrical components you're likely to come across in our tutorials and various other electrical projects.
  • Resistor
  • Capacitor
  • Inductor
  • Diode
  • LED
  • Transistor
  • IC- Chips
Below we'll first present the 'schematic' symbol used in electronic drawings, followed by examples of physical components with leads (wires) as well as the now more common 'surface mount' version of the devices. As you can imagine, there are many variations, and technology is always changing, so we will look at only a sampling of devices found in common projects and component packages.

Resistor




Symbol
With leads
Surface Mount

Resistors 'resist' the flow of electrical current. You may want to think of resistance as the diameter of a pipe or hose. The bigger the hose, the lower the resistance to water flowing in it (a fire hose). A drinking straw would have higher resistance.

Resistors are used to limit the current in a circuit. A voltage divider is often constructed using two resistors. The ratio of the resistors 'split' or divide the voltage.

A battery 'E' provides the voltage, which is divided down by resistor R1 and R2.

Vout = E x R1/(R1+R2)

Resistors dissipate energy and can get warm/hot such as those in hair-dryers, heaters and powered electronics. The resistance value in Ohms and it's power rating are important. Color bands are printed on resistors to identify their value. A table is provided above to show how to decode the value.

Capacitor



Symbol
With leads
Surface Mount

A capacitor is a storage device. It is made from two metal plates separated by air or other non-conducting materials. You can think of a capacitor as a tiny battery, (or a glass of water). A capacitor stores electric charge by creating an electric field. It is used to make the output of a power supply smooth, for timing circuits (oscillators) and filters. The capacitor value in Farads and it's voltage rating are important. A capacitor tries to keep the voltage constant across its terminal.

Inductor



Symbol
With leads
Surface Mount

An inductor (coil or choke) is also an energy storage device. It is made by winding wire in a coil with air or other (core) materials. An inductor stores energy in a magnetic field. Inductors are used in power supplies, and Radio Frequency equipment. The inductor value in Henrys and it's current rating are important. An inductor tries to keep the current constant across it's terminal. Rapidly disconnecting an inductor can produce large voltage spikes. These spikes can damage components if the energy released in not managed with other devices. Coils are the base of many other components such as transformers, relays, speakers and motors.

Diode



Symbol
With leads
Surface Mount

Diodes are semiconductor devices, that allow current to flow in only one-direction. You can think of them as one-way streets. Diodes are used to convert AC (Alternating Current) into DC (Direct Current). Diodes are used in power supplies, simple AM radios and as protection devices. The voltage and current ratings are important. Since diodes are one-way street, it matters which way they are installed in a circuit.

LED



Symbol
With leads
Surface Mount

LED (Light Emitting Diodes) are special diodes that emit light of different wavelengths (color) based on their chemistry and construction. Since LEDs are diodes, they must be installed to allow current to flow (one-way). The LED will not light if it is installed backwards in the circuit. LEDs are current driven devices (not voltage).  An LED requires about 10 mA (milliamperes) to produce light. (5-20mA range). When current flows through an LED the voltage present across its terminal will depend on the LED color (chemistry): red, yellow, green LEDs flow at about 2V. Infrared LEDs flow at about 1.7V and blue or white LEDs flow at around 3.2V. In order to limit the current of an LED we need to use a resistor.

Here is how to calculate the resistor value required.

For E=5V and a RED LED (2V), we have:

R= (5V-2V)/10mA = 3/0.01 = 300 Ohms
The closest common value is 330 ohms so we would use this value.

For E=9V, this would be 680 or 1,000 Ohms.

Note: There are many models of LEDs (some brighter than others). The brightness can be 'adjusted' a bit by choosing resistor values above or below to suit the light level needed.  Do not exceed 25mA for common LEDs. Also note that the battery or power source must be greater than the LED voltage.
A 1.5V AA battery will not light an LED directly. Use 2 x AA for 3V.

Transistor



Symbol
With leads
Surface Mount

Transistor are semiconductor devices that are used as electronic switches or signal amplifiers. There are three pins. A small control signal on the "B" (base) pin allows a larger current to flow in the "C" (collector) and "E" (emitter) terminals.  This allows a transistor to 'boost' the signal at "B" coming from an IC to drive other circuits that require more current than the IC can provide.

There are two complementary versions: NPN and PNP,  they operate in opposite fashion (polarity) from each other. A current limiting resistor is required for the "B" terminal. A transistor will act as an amplifier if the base signal is changed slightly from a set operating (bias) point.

IC-Intergrated Circuit - 'Chips'




Symbol
With leads
Surface Mount

An IC (chip) is an Integrated Circuit. Using microelectronic technology many components are 'printed' on a silicon wafer and packaged with an epoxy body to protect it. Many components (millions) can be packed into a single package to make complex functions such as computers.
ICs can performs a large variety of functions.

Going Further

This is just a very brief introduction. Manufacturer product datasheets are a good place to learn about electronic components.