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Introduction to Electronics

Introduction to Electronics | Current, Voltage, and Resistance | Magnitude, Frequency, and Measurements | Duty Cycle | Laboratory Equipment | Engineering Math | Tutorials | Study Tools | Practice Exercises

Introduction to Electronics

Electricity is the result of electrons moving through matter. Electrons, protons, and neutrons make up an atom. In the standard model, electrons orbit the nucleus (made up of protons and neutrons) at defined distances, called shells. In certain materials, such as metals, the attraction of the nucleus to the electron is weak, so electrons randomly move from atom to atom when one or more electrons are missing in the atom's outer shell (valence). An illustration of this electron movement is displayed below.

Electricity can be generated in various ways. It can be generated using nonrenewable sources such as fossil fuels (e.g., oil) or renewable sources, such as water, wind, and the sun. We use chemical processes (e.g., batteries), solar energy (e.g., wind turbines), water (e.g., waterwheels and turbines), and mechanical sources (e.g., manual- and mechanical-driven dynamo) to generate electricity. An electrical source is needed to make electrons move; a load is needed to convert the electric source to a useful form; a path is needed to convey the electrons to the load; the source connected to the load, via the path, completes the circuit.

Electrons can only move freely through certain types of material. Physical items are categorized as one of three types of material with respect to how they respond to electricity: (a) conductor, (b) semiconductor, or(c) insulator. Electrons can move freely through conductive material, and under certain conditions, through semiconductive material. Electrons are generally not able to move through insulators.

Conductors are normally made of metal (e.g., copper, silver, and gold are good conductors). In electrical circuits, conductors, also called wires, are the path between the source and the load or loads. Semiconductors are made of material such as silicon and germanium. Semiconductor material makes up most of the integrated circuits that are used in the digital devices (e.g., transistors, microprocessors, and memory).

Semiconductive material that is used to make electronic devices, such as transistors, integrated circuits (ICs), and diodes, is illustrated below.

Insulators, through which no electrons are supposed to move, are made of material such as glass, rubber, or wood. These and other insulators can be made conductive by formulation (i.e., adding something in the manufacturing process to make conductive rubber) or by depositing a thin metal film on the surface, such as a mirror or metalized plastic balloon. An illustration of a conductor with insulation is shown below.

This AC wall plug looks similar to power cords that are on washing machines, dryers, refrigerators, or many other devices. This device has metallic conductors for the prongs (three connectors) that plug into your wall outlet and it has insulation (the yellow material) to protect you from being exposed to the power when you plug it into the wall.

The study of electronics requires you to familiarize yourself with many different concepts and devices. We'll use ICs in this class, and you will begin using transistors in a later course. As you begin using these components, it will be less confusing to you if you've seen some of them beforehand. Some components you use or will be using are illustrated below.

Electronic components, such as those pictured above, will be used in many of the circuits that you will build and test. Batteries offer you a source of power, switches allow you to control the power with an on or off function on a circuit, and LEDs can be used as indicators (loads) for various circuit conditions.

Current, Voltage, and Resistance

Voltage is the electrical pressure that causes a current flow (movement of electrons) through a completed electrical circuit. Connecting a voltage source, such as a power supply, to an electrical load, such as a resistor, will cause current to flow through a circuit. Voltage can be defined as the energy per unit of charge and is measured in volts, represented by the symbol V.

Current is the electrical flow of electrons responding to voltage being applied to an electrical circuit. Current is the movement of electrons through a completed circuit. Current can be defined as the rate of flow for a charge and is represented by the symbol I. Current is measured in amperes or amps (A is the symbol for amp.)

Resistance is the electrical limit to the amount of current flowing through an electrical circuit. Resistance establishes the amount of current flow in a circuit based on the amount of voltage being applied. Resistance can be defined as the opposition to current flow and is represented by the symbol R. Resistance is measured in ohms, represented by the Greek letter omega ().

Magnitude, Frequency, and Measurements

Electrical signals have several characteristics related to time and quantity. An electrical signal may be nonchanging (direct current, called DC), or change at a repetitive rate (alternating current, called AC). For signals that change at a repetitive rate, the rate at which the signal repeats is called its frequency. Frequency can be defined as the number of occurrences within a given period.

An electrical signal contains a certain amount of potential to cause electron flow. This potential is called the signal's magnitude. The use of engineering notation is valuable when describing a time and potential-related characteristic of a signal. The very large and very small numeric values required to express the different electrical characteristics that we measure, calculate, and report are expressed in engineering and/or scientific notation. Examples of the two most common forms used in engineering technology, scientific and engineering notation, are explained below.

DC and AC signals both have time- and potential-related characteristics. DC signals do not change with time (they remain constant), in contrast to an AC signal that changes at a periodic rate. An electrical signal's potential is described in terms of its voltage.

An example of a voltage source is a battery. We use them to power our cell phones, laptops, remote controls, cars, and numerous other devices that require electrical energy. Batteries are DC sources, but there are many AC sources that you use as well.

DC voltages are constant. If a battery for your remote control is a 1.5 V battery, that voltage is a constant value. The voltage will appear constant if you measure it with a signal-measuring instrument such as a digital multimeter (DMM). An illustration of a DC voltage being read by a DMM is shown below.

The value 4.48 represents DC Voltage, as indicated in the top right-hand corner of the meter's display. It is always measured in Volts Direct Current (VDC).

Another measuring tool, the oscilloscope, displays voltage as a function of time. In the case of a DC voltage, the oscilloscope shows a constant value as a straight line on its display. Here's an illustration of this value:

Oscilloscopes only display voltages versus time, and this one, being a straight line from left to right, is nonchanging, so it must be DC. The value of the reading is determined by counting how many small and large horizontal lines the measured value is away from the reference point (in this case, Ground or 0 VDC), and how many volts each horizontal line represents (in this case, 1 V for each large horizontal line). In this example, there are three large horizontal lines between the signal and ground and two small horizontal lines. The value of the measurement is (3 divisions x 1 volt/division) + (2 small divisions x 0.2 volts/small division) = 3.4 V. As you can see, the oscilloscope is generally not as accurate as the DMM for measuring voltage. The oscilloscope is advantageous for measuring signals that change with time.

An example of an AC voltage source is the wall socket in your apartment, home, or office. The operating voltage in the U.S. is 110 Vac at a frequency of 60 Hz (Hz is the abbreviation for Hertz, or repetitions per second). You use this AC voltage when you charge your cell phone, turn on the lights in your apartment or home, and turn on a washing machine or dryer. An AC voltage is always changing with respect to time. When you see an AC signal displayed on an oscilloscope, it would look like the following reading:

This AC signal above is moving up and down over time, and the voltage is always changing as the signal moves from one point to the next. If you notice, the wave looks the same as you go from the far left-hand side to the middle of the display as it does when you go from the middle of the display to the far right-hand side. This is one cycle of the waveform (how long it takes before it begins to repeat). The voltage displayed on an oscilloscope depends on the scale of the vertical axis; the time elapsed depends on the scale of the horizontal axis.

AC voltages can be measured in several ways: peak-to-peak (pk-pk), top to bottom; peak (pk), from middle to top or middle to bottom; root mean squared (rms), a calculated value; and average (avg), a calculated value.

The AC voltage measurement of the signal shown above, if the horizontal lines represent 1V per major line (division), could be:

The waveform goes 1.5 divisions above the center horizontal line and 1.5 divisions below the center horizontal line. That is a total of three major divisions, and if each one represents 1V/division, then you multiply 3 by 1 V/division = 3 Vacpk-pk.

The peak voltage is found by how far the AC signal goes above or below the center line. In this case, that's 1.5 divisions. If each major division represents 1V/division, the value is 1.5 Vacpk.

The rms voltage is calculated by multiplying the peak voltage by 0.707. In this case, the result of 1.5 Vpk x 0.707 = 1.0605 Vacrms. Finally, the average voltage is calculated by multiplying the peak voltage by 0.636. In this case, the result of 1.5 Vpk x 0.636 = 0.954 Vacavg. RMS and average AC voltage readings are used to describe AC signals and will be fully explained in a later course.

The amount of time it takes a repetitive signal to return to its starting point is the time to move one cycle. This time is measured in seconds (or portions of seconds) and is the AC signal's Time Period, or simply, inverse of the signal's frequency.

Frequency is the rate at which a changing, repetitive waveform repeats itself in one second. Frequency is measured in hertz (Hz) and is the reciprocal of time. One hertz has a rate of one cycle per second. As mentioned earlier, AC wall outlets in the U.S. generate a 110 Vacrms voltage at 60 Hz. That means the amount of time it takes an AC waveform to travel one cycle is 1/60 Hz = 0.0167 seconds.

The horizontal dimensions on the oscilloscope represent time. If each major division shown on the illustration of our AC waveform represents 0.001 seconds, we can determine the Time Period of this waveform and its frequency. Its time period is found by moving across, from the left-hand side, until we find where the AC signal is in the same location: In this example, that's five major divisions (in the middle of the display).

To calculate the time period and the frequency of this AC signal, we begin by finding the period. We do this by multiplying the number of major divisions it takes the signal to repeat by the amount of time each division represents. In our example, this is 0.001 seconds/division x 5 divisions = 0.005 seconds or 5 msec. We find the frequency (f) by taking the reciprocal the period. In this case, the calculation 1/0.005 seconds = 200 Hz provides the frequency of this waveform.

The equations for this reciprocal relationship are f(Hz) = 1/T(sec) or T(sec) = 1/f(Hz).

Repetitive signals can have various shapes. The three most widely used shapes are sine wave, square wave, and triangular wave. Each one of these wave shapes is used to perform unique functions in electronic circuitry. Here are brief descriptions and some illustrations of three basic AC waveforms.

A sine wave is shown below:

The sine wave illustrated above has traveled one cycle between the points shown by the arrow B. These particular points in the waveform are called the positive peak points.

An illustration of a square wave is shown below:

In the square wave above, the waveform travels one cycle from points A to E.

A third general shape, the triangular wave, is shown below.

Duty Cycle

A periodic, or repetitive waveform, does not have to be symmetrical in shape, which means that we can take a square wave and modify its shape to make it rectangular. This change affects the duty cycle of the waveform (amount of time a pulsating DC signal is high divided by the period ). We use rectangular waves in various electronic control and communication systems. A rectangular waveform could look like the one illustrated below:

In this example, one cycle can be defined either as starting at Point 1 and ending at Point 3, or starting at Point 2 and ending at Point 4. Since the amount of time the signal is high is not equal to the amount of time the signal is low, this wave shape is rectangular.

In this example, the amount of time to go from Point 1 to 2 is twice the amount of time to go from Point 2 to 3. The amount of time between Points 1 and 2 is when the signal is high; the amount of time between Points 2 and 3 is when the signal is low. The sum of these two values is the Time Period. The duty cycle can be calculated in the following way:

Varying the duty cycle can be useful in motor control, sequencing a digital system, and charging batteries and many other applications that you will use. You can generate these signals via software (write a program to output a waveform) or in hardware (design an electronic circuit that will create a waveform).

Laboratory Equipment

All electrical signals need to be created and observed using standard electronic lab equipment. This equipment allows you to apply voltages (DC or AC) to an electrical circuit, causing it to be activated. The various characteristics of an electrical circuit can be measured to determine if it's working properly by using equipment such as a DMM and an oscilloscope. The specific equipments you will be using are described in detail in the LabPrep section of the Course Home Tab.

MultiSim Simulations

Validation of signal measurements or calculations is accomplished with computer simulation of electrical signal and/or circuit behavior as a part of the analysis process in the study of electronics. Simulation helps confirm our calculations for a particular circuit's component values and the interaction of these devices. The proper use and understanding of simulators can save us a great bit of time and money when we are designing or analyzing electrical circuits. A simulation package that allows us to evaluate both digital and analog signals is MultiSim. It is an easy tool to use and very powerful in functionality.

MultiSim will be covered in your lab assignment and will be used throughout the semester. You will be given detailed instructions on how to use it and the functionality it offers.

Engineering Math

Numbers and Units

Numbers can be represented in multiple ways and still have the same meaning. To better understand how a numeric value can be represented in different forms but remain the same value, let us begin with the number system with which we are most familiar: the decimal system. To simplify further matters, we will evaluate a decimal system application with which you are also familiar: money (or currency).

We can have a specific amount of money, but it can be described in different ways, depending on our reference for the amount. For example, $100.00 means one hundred dollars in reference to dollars. When we describe it in terms of thousand dollar units, it is 1/10th of a thousand dollars. The amount of money did not change; only the reference changed.

If we want to refer to it differently, $100.00 is also 1000 dimes. This reference may make us think that we have more money, but the amount remains the same, unfortunately. Again, only the reference (from dollar to dime) changed. We will need to become very familiar with this concept as we learn new references and revisit others.

You will develop a good understanding of ways to represent different numbers, as well as ways to convert numbers from one form to another. Remember, however, that the number will still be the same, but you may need to express it in another manner (different base, different unit of measure, etc.).

An example of a digit in a positional number system having different meanings can be illustrated by starting with the number 4 in the decimal system (a positional number system). The number 4 represents four units of ones. When we evaluate the decimal number 240, however, the 4 now represents four units of tens (because of its position in the number 240).

Another example of this could be the number 0.34. In this case, the digit 4 represents four-one hundredths of a unit. Again, the placement of the digit 4 has everything to do with what value it has.

Powers of Ten Math

As mentioned earlier, many of the values used in Engineering Technology range from very large to very small. To handle these values, and to avoid excessive use of digits, we rely extensively on the use of exponential notation. To perform basic arithmetic functions on decimal numbers (or other positional number systems) using exponents, the following rules need to be followed, as demonstrated by the examples of five basic math operations:

• Addition

3x10+3 + 2x10+3 = 5x10+3

Make the numbers have the same exponential values (in this example, both already have 3 as their exponent, so there is no need to change the exponent's value), add the numbers without their powers of ten (2 + 3 = 5), and then multiply the sum by the power of ten (10⁺³). Pay attention to the sign of each exponent's value, making sure that you perform signed mathematical operations properly.

• Subtraction

3x10+4 - 2x10+3 = 30x10+3 - 2x10+3 = 28x10+3

Make the numbers have the same exponential values by changing either exponent (in this example, +4 is changed to +3), subtract the numbers without their powers of ten (30 - 2 = 28), and then multiply the difference by the same power of ten (10⁺³). Pay attention to the sign of each exponent's value, making sure that you perform signed mathematical operations properly.

• Multiplication

300x10+5 x 2x10+3 = 600x10<(+5) + (+3)> = 600x10+8

Multiply the numbers (300 x 2 = 600), add the exponential powers together {<(+5) + (+3)> = (+8)}, and then multiply the product by the new power of ten (10⁺⁸). Notice that for multiplication, there is no need to make the exponents the same before performing the operation. Pay attention to the sign of each exponent's value, making sure that you perform signed mathematical operations properly.

• Division

3000x10+3 / 2x10+2 = 1500x10<(+3) - (+2)> = 1500x10+1

Divide the numerator (3000) by the denominator (2) without the powers of ten (1500), subtract the exponential power of the denominator from the numerator {<(+3) - (+2)> = (+1)}, and then multiply the result of your division (3000/2 = 1500) by the power of ten (1500x10⁺¹). Notice that, in the case of division, there is no need to make the exponents the same before performing the operation. Pay attention to the sign of each exponent's value, making sure that you perform signed mathematical operations properly.

• Reciprocation

1/(2x10+3)= 0.5x10-3

Divide the numerator by the denominator without the power of ten (1/2 = 0.5), change the sign of the denominator's exponent (+3 to -3), then multiply the new power of ten (10^-3) by the result of the division.

Engineering Notation

Engineering notation is used extensively in electronics. Your lab equipment, component values, and electrical properties all use engineering notation to express values. Engineering notation is similar to, but slightly different from scientific notation.

Engineering notation is simply a way to express a numeric value in a different form. The value of the number does not change, it is just represented differently.

In engineering notation, the process to create the value must meet two requirements: to find out where the decimal point needs to go so that you can have one to three digits to the left of the decimal point; and to create an exponent that is a multiple of 3 (0 is considered a multiple of 3). Below is an example of engineering notation.

The process to convert this number to engineering notation is as listed:

1. Find out what multiple of 3 you need in order to make the number have one to three digits to the left of the decimal point (34, in the case above) and ensure that the exponential power of 10 is a power of 3 (+3, in this case).
2. Add or subtract powers of 10 based on how many digits the decimal point needs to be moved, so that your number has the same value. (In this case, the decimal point is moved three places to the left, meaning the exponential power of 10 is increased once per numeric position, beginning at 0; thus 0 + 3 = 3 ). When both of these (exponential and numeric values) have been determined, they are multiplied to create the final term (34.536x10⁺³).

Below is an example of engineering notation.

The decimal point would need to go between the 1 and 7 so that both criteria are met (exponent multiple of 3 and one to three digits for number). The decimal point, in this example, was moved to the right three times and the number will have three digits (one to three digits). The sign of the exponent is found based on the direction that the decimal point moves and how many digit locations it moves. In this case, the decimal point moved three places to the right, causing the exponential value to decrease by one for every position it is moved. This is how we went from 0 to -3.

Engineering notation has its own naming convention (metric prefixes) to represent the various multiples of exponential powers of three. Here are some of them:

These symbols are used as shorthand to help us represent larger and smaller electrical values. If we are trying to represent a large voltage (potential energy, measured in volts, abbreviated V), we can express 120,000 V as 120 kV. This was determined using the same rules we saw above for creating a term in engineering notation (120,000 V = 120x10⁺³ V= 120 kV).

Scientific Notation

Scientific notation is another method used to express a numeric value in a different form. In scientific notation, the numeric value must have two parts: a power of ten value (exponential power of ten) and a single digit value (one decimal digit) to the left of the decimal point. Below is an example of scientific notation.

The process to create this scientific value is listed in the following steps:

1. Find out where the decimal point would need to go (in this case, between the 3 and the 4 in order to give you one digit to the left of the decimal point) and place it between the single digit and the other digits.
2. Add or subtract powers of 10 based on how many digits the decimal point needs to be moved so that your number has the same value. (In this case, the decimal point is moved four places to the left, meaning that the exponential power of 10 is increased once per numeric position, beginning at 0; thus 0 + 4 = 4).
3. Once the exponential value is known (+4) and the decimal point has been placed properly in the number (3.4536), these values are multiplied (3.4536 x 10⁺⁴).

To find the exponent's value, remember this rule: The exponent increases by one every time it moves one place to the left and decrease by one every time it moves one place to the right.

Another example of creating the scientific notation for a number is illustrated below. In this case, we've got a value less than 1 to begin with, so pay close attention to its scientifically notated form.

The scientific notation for this fraction is created the same way we created the first one. First, we placed the decimal point in the numeric position that would give us only one digit to the left of the decimal point (between 7 and 8). Then, we counted how many positions the decimal point moved (5 positions) and determined what direction it moved (right). The number of positions (5) yielded the exponent value (5), and the direction it moved gave us the exponent's sign (negative).

Rounding

Rounding off numbers allows you to work with numbers that have meaning to you without dealing with their long fractional portions. The basic rule for rounding off numbers is straightforward: given a certain number of significant digits following the decimal point (for the fractional portion of a number), go one digit past that position and evaluate the digit's value. If the value is 5 or larger, then add one to the digit to the left of it (rounding up). If the value is 4 or smaller, then do not change the value of the digit to the left of the number (rounding down). The remaining digits following the significant digit are eliminated from the final value.

An example is 0.0056 rounded off to two significant digits past the decimal point (to the right of it). Move two digits to the right and you find the value 0, followed by the digit 5 (the third digit in numeric value after the decimal point). Since the number is to be rounded off to two significant digits, we evaluate the third digit and find that its value is 5. Since 5 is 5 or greater, we add 1 to the value to the left of it, which is currently 0. This number, rounded off to two significant digits past the decimal point, becomes 0.01.

Another example is 3567.234 rounded off to one significant digit past the decimal point (to the right of the decimal point). In this case, the digit following the first digit (one significant digit) after the decimal point is 3 (the second digit after decimal point one past significant digit location). In this case, 3 is less than 5, so no change would occur to the first digit past the decimal point. The final value, rounded properly to one significant digit past the decimal point, is 3567.2.

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Scientific Notation

Rules of Significance

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