Basic Electronics

2006-05-25T07:55:00.000-07:00

BASIC ELECTRONIC CIRCUITS EXPLAINED

In this section we will discuss what a circuit is. I won't belabor the principles of the atom -- let a physics text handle that (boring) task. Instead let's talk about the facts you will need to know to get started in electronics. Circuit A circuit is a path for electrons to flow through. The path is from a power sources negative terminal, through the various components and on to the positive terminal. Think of it as a circle. The paths may split off here and there but they always for a line from the negative to positive. NOTE: Negatively charged electrons in a conductor are attracted to the positive side of the power source.

Conductor A conductor is a material (usually a metal such as copper) that allows electrical current to pass easily through. The current is made up of electrons. This is opposed to an insulator which prevents the flow of electricity through it.

Simple Circuit If we break a circuit down to it's elementary blocks we get: 1) A Power Source -- eg: battery 2) A Path -- eg: a wire 3) A Load -- eg: a lamp 4) A Control -- eg: switch (Optional) 5) An indicator -- eg: Meter (Optional)

	Series Circuit A series circuit is one with all the loads in a row. Like links in a chain. There is only ONE path for the electricity to flow. If this circuit was a string of light bulbs, and one blew out, the remaining bulbs would turn off. There is specific properties to this circuit that will be described in another section. NOTE: The squiggly lines in the diagram are the symbol for Resistors. The parallel lines are the symbol for a battery.

Parallel Circuit A parallel circuit is one that has two or more paths for the electricity to flow. In other words, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out there is still current flowing to the others as they are still in a direct path from the negative to positive terminals of the battery. There are also specific properties a parallel this circuit that will be described in another section.

	Combination Circuit A combination circuit is one that has a "combination" of series and parallel paths for the electricity to flow. Its properties are a synthesis of the two. In this example, the parallel section of the circuit is like a sub-circuit and actually is part of an over-all series circuit.

VOLTAGE, CURRENT & RESISTANCE EXPLAINED

In electronics we are dealing with voltage, current and resistance in circuits. In the next section well will learn that using Ohm's Law we can determine one of these values by knowing the other two. So it is importance to firmly grasp what these three terms mean first.

We will describe these electrical terms using an analog that closely resembles electronics � HYDRAULICS.

Voltage
Voltage is the electrical force, or "pressure", that causes current to flow in a circuit. It is measured in VOLTS (V or E). Take a look at the diagram. Voltage would be the force that is pushing the water (electrons) forward.

Current
Current is the movement of electrical charge - the flow of electrons through the electronic circuit. Current is measured in AMPERES (AMPS, A or I). Current would be the flow of water moving through the tube (wire).

Resistance
Resistance is anything that causes an opposition to the flow of electricity in a circuit. It is used to control the amount of voltage and/or amperage in a circuit. Everything in the circuit causes a resistance (even wire). It is measured in OHMS (W).
OHM�S LAW EXPLAINED

�The amount of current flowing in a circuit made up of pure resistances is directly proportional to the electromotive forces impressed on the circuit and inversely proportional to the total resistance of the circuit.�

Don�t let that quote scare you. It is not as scholarly as it sounds.

Before going further make sure you understand:
� What composes a circuit.
� What voltage, current and resistance are.

In simpler terms, Ohm�s Law means:
1) A steady increase in voltage, in a circuit with constant resistance,
produces a constant linear rise in current.

2) A steady increase in resistance, in a circuit with constant voltage,
produces a progressively (not a straight-line if graphed) weaker current.

Ohm�s Law is a set of formulas used in electronics to calculate an unknown amount of current, voltage or reistance. It was named after the German physicist Georg Simon Ohm. Born 1787. Died 1854.

Knowledge of this Law is often under-estimated by beginners. I have talked to people that can design complex circuitry and microprocessor systems that have said, �Ohm�s Law? What�s that?�.

Unless you know this basic fundemental building block of electronics, you will never have a strong foundation to hold up the electronics towers you will be constructing in the future. Learn Ohm�s Law. Learn it inside and out!

TECHNICAL DEFINITION ALERT!

Ohm's Law is a formulation of the relationship of voltage, current, and resistance, expressed as:

Where:
V is the Voltage measured in volts
I is the Current measured in amperes
R is the resistance measured in Ohms Therefore: Volts = Amps times Resistance

Ohms Law is used to calculate a missing value in a circuit

In this simple circuit there is a current of 12 amps (12A) and a resistive load of 1 Ohm (1W). Using the first formula from above we determine the Voltage: V = 12 x 1 : V = 12 Volts (12V)

If we knew the battery was suppling 12 volt of pressure (voltage), and there was a resistive load of 1 Ohm placed in series, the current would be: I = 12 / 1 : I = 12 Amps (12A)

If we knew the battery was suppling 12V and the current being generated was 12A, then the Resistance would be: R = 12/12 : R = 1W

Be sure to check out the Ohm's Calculator to help you determine circuit values.

Note: Remember a battery is not measured in amperage as is commonly believed with beginners to electronics. The battery supplies the pressure that creates the flow (current) in a given circuit. The amperage rating on a battery is "How long the battery will last for one hour while driving a circuit of that amperage". It is measured in Amperage-Hours. So a 1000mAh would last for 1 hour in a one amp circuit. (1000mAh is 1A for one hour)

An easy way to remember the formulas is by using this diagram.

To determine a missing value, cover it with your finger. The horizontal line in the middle means to divide the two remaining values. The "X" in the bottom section of the circle means to multiply the remaining values.

� If you are calculating voltage, cover it and you have I X R left (V= I times R).

� If you are calculating amperage, cover it, and you have V divided by R left (I=V/R).

� If you are calculating resistance, cover it, and you have V divide by I left (R=V/I).
Note: The letter E is sometimes used instead of V for voltage.

Resistor Color Codes & Primer

Common Resistor

Resistors are color coded for easy reading. Imagine how many blind technicians there would be otherwise.

To determine the value of a given resistor look for the gold or silver tolorance band and rotate the resistor as in the photo above.(Tolerance band to the right). Look at the 1st color band and determine its color. This maybe difficult on small or oddly colored resistors. Now look at the chart and match the "1st & 2nd color band" color to the "Digit it represents". Write this number down.

Example:

First color is red which is 2
Second color is black which is 0
third color is yellow which is 10,000
Torerance is silver which is 10%

Therefore the equation is:

2 0 x 10,000 = 200,000 Ohms
Tolerances
Gold= 5%
Silver=10%
None=20%

Resistor Color Code Chart

1st. & 2nd Color Band Digit it Represents
-----Multiplier-----

BLACK
0

X1

BROWN
1

X10

RED
2

X100

ORANGE
3

X1,000 or 1K

YELLOW
4

X10,000 or 10K

GREEN
5
X100,000 or 100K

BLUE
6

X1,000,000 or 1M

VIOLET
7
Silver is divide by 100

GRAY
8
Gold is divide by 10

WHITE

Now look at the 2nd color band and match that color to the same chart. Write this number next to the 1st Digit.

The Last color band is the number you will multiply the result by. Match the 3rd color band with the chart under multiplier. This is the number you will mulitple the other 2 numbers by. Write it next to the other 2 numbers with a multiplication sign before it. Example : 2 2 x 1,000.

To pull it all together now, simply multiply the first 2 numbers (1st number in the tens column and 2nd in the ones column) by the Multiplier.

Tolerance Explanation

Resistors are never the exact value that the color codes indicate.Therefore manufacturers place a tolerance color band on the resistor to tell you just how accurate this resistor is made. It is simply a measurment of the imperfections. Gold means the resistor is within 5% of being dead-on accurate. Silver being within 10% and no color band being within 20%. To determine the exact range that the resistor may be, take the value of the resistor and mutiply it by 5,10, 0r 20%. That is the number that the resistor may go either way.

Example: A 1,000 Ohm resistor with a gold band maybe any value between 950 to 1050 Ohms.

Example: A 22,000 Ohm resistor with a silver band maybe any value between 19,800 and 24,200 Ohms.

FAQ

Just a few common questions to help you out.
1) Which side of the resistor do I read from?
The Gold or Silver band is always set to the right, then you read from left to right. Sometimes there will be no tolerance band -- Simply find the side that has a band closest to a lead and make that the first band.
2) Sometimes the colors are hard to make out. How do I make certain what the value of the resistor really is?
Occasionally the colors are jumbled or burnt off. The only way to read it then is with a multimeter across the leads
3) How do I remember this sequence of colors?
Remember the color codes with this sentence: Big Brown Rabbits Often Yield Great Big Vocal Groans When Gingerly Slapped.

SCHEMATIC SYMBOLS

These are common schematic symbols used in electronics.

SEMICONDUCTOR SYMBOLS

IDENTIFYING ELECTRONIC COMPONENTS - PASSIVE

When a beginner to electronics first looks at a circuit board full of components he/she is often overwhelmed by the diversity of do-dads. In these next few sections we will help you to identify some of the simple components and their schematical symbol. Then you should be able to call them resistors and transistors instead of "Whatchamacallits". In later sections we will go into the workings of each component. Just try to familiarize yourself with the basics for now.

Electronic component are classed into either being Passive devices or Active devices.

A Passive Device is one that contributes no power gain (amplification) to a circuit or system. It has not control action and does not require any input other than a signal to perform its function. In other words, "A components with no brains!" Examples are Resistors, Capactitors and Inductors

Active Devices are components that are capable of controlling voltages or currents and can create a switching action in the circuit. In other words, "Devices with smarts!" Examples are Diodes, Transistors and Integrated circuits.

Resistors:
This is the most common component in electronics. It is used mainly to control current and voltage within the circuit. You can identify a simple resistor by its simple cigar shape with a wire lead coming out of each end. It uses a system of color coded bands to identify the value of the component (measured in Ohms) *A surface mount resistor is in fact mere millimeters in size but performs the same function as its bigger brother, the simple resistor. A potentiometer is a variable resistor. It lets you vary the resistance with a dial or sliding control in order to alter current or voltage on the fly. This is opposed to the "fixed" simple resistors.

Capacitors:
Capacitors, or "caps", vary in size and shape - from a small surface mount model up to a huge electric motor cap the size of a paint can. Whatever the size or shape, the purpose is the same - It storages electrical energy in the form of electrostatic charge. We will get into the mechanics and further properties of this later. The size of a capacitor generally determines how much charge it can store. A small surface mount or ceramic cap will only hold a minuscule charge. A cylindrical electrolytic cap will store a much larger charge. Some of the large electrolytic caps can store enough charge to kill a person. Another type, called Tantalum Capacitors, store a larger charge in a smaller package.

Inductors:
You may remember from science class that adding electrical current to a coil of wire produces a magnetic field around itself. This is how the inductor works. It is charged with a magnetic field and when that field collapses it produces current in the opposite direction. Inductors are used in Alternating Current circuits to oppose changes in the existing current. The mechanics of this will be described later. Most inductors can be identified by the "coil" appearance. Others actually look like a resistor but are usually green in color.
A. Air Core, B. Iron Core, C. Powered Metal Core.

IDENTIFYING ELECTRONIC COMPONENTS - ACTIVE

When a beginner to electronics first looks at a circuit board full of components he/she is often overwhelmed by the diversity of do-dads. In these next few sections we will help you to identify some of the simple components and their schematical symbol. Then you should be able to call them resistors and transistors instead of "Whatchamacallits". In later sections we will go into the workings of each component. Just try to familiarize yourself with the basics for now.

Electronic component are classed into either being Passive devices or Active devices.

Active Devices are components that are capable of controlling voltages or currents and can create a switching action in the circuit. In other words, "Devices with smarts!" Examples are Diodes, Transistors and Integrated circuits.

NOTE: Most Active components are semiconductors. More on this in later sections.

A Passive Device is one that contributes no power gain (amplification) to a circuit or system. It has not control action and does not require any input other than a signal to perform its function. In other words, "A components with no brains!" Examples are Resistors, Capactitors and Inductors

Diodes:
Diodes are basically a one-way valve for electrical current. They let it flow in one direction (from positive to negative) and not in the other direction. Most diodes are similar in appearance to a resistor and will have a painted line on one end showing the direction or flow (white side is negative). If the negative side is on the negative end of the circuit, current will flow. If the negative is on the positive side of the circuit no current will flow. More on diodes in later sections.

LEDs: Light Emitting Diodes:
LEDs are simply diodes that emit light of one form or another. They are used as indicator devices. Example: LED lit equals machine on. They come in several sizes and colors. Some even emit Infrared Light which cannot be seen by the human eye.

Transistors:
The transistor is possibly the most important invention of this decade. I performs two basic functions. 1) It acts as a switch turning current on and off. 2) It acts as a amplifier. This makes an output signal that is a magnified version of the input signal. More on transistors in later sections.
Transistors come in several sizes depending on their application. It can be a big power transistor such as is used in power applifiers in your stereo, down to a surface mount (SMT) and even down to .5 microns wide( I.E.: Mucho Small!) such as in a microprocessor or Integrated Circuit.

ICs -Integrated Circuits:
Integrated Circuits, or ICs, are complex circuits inside one simple package. Silicon and metals are used to simulate resistors, capacitors, transistors, etc. It is a space saving miracle. These components come in a wide variety of packages and sizes. You can tell them by their "monolithic shape" that has a ton of "pins" coming out of them. Their applications are as varied as their packages. It can be a simple timer, to a complex logic circuit, or even a microcontroller (microprocessor with a few added functions) with erasable memory built inside.

Microprocessors (MPUs):
Microprocessors and other large scale ICs are very complex ICs. At their core is the transistor which provides the logic for computers, cars, TVs and just about everything else electronic. Packages are becoming smaller and smaller as companies are learning new tricks to make the transistors ever tinier.