Chapter 4

1. Chapter 4 The Electronic Computer Age

2. Electronics • The use of electronics has completely changed our world in the last hundred years. • The electric light has extended our day. • Electric appliances in the kitchen allow us to keep our food longer and prepare it more quickly. • Other electric appliances have reduced the amount of time we spend on work, giving us more free time. • Electronic entertainment has changed the way we spend our free time.

3. The smallest pieces of our world • All materials are made up of tiny particles called atoms. Materials made up of only one kind are called elements. • Iron and carbon are examples of elements. • Only 103 elements are known to exist. • An atom is the smallest part of an element that can exist and still have all the properties of that element. • Atoms are so small that you cannot see them, even with the most powerful optical microscope.

4. The smallest pieces of our world… • Atoms of different kinds may be combined to make materials called compounds. • When a compound is formed from two or more elements, it has properties all its own. • It may be nothing like the elements it is made of. • For example, sodium, a poisonous metal that reacts violently when it touches water, makes a compound with chlorine, a poisonous gas. The compound sodium chloride, or common table salt.

5. Atoms… • Atoms are made up of even smaller particles. These particles do not have the properties of the element. • They have their own properties. Atoms have a center part called a nucleus. • The nucleus is made up of protons and neutrons. Smaller particles called electrons circle the nucleus very rapidly.

6. What does that mean? • The number of protons in an atom determines the kind of element it is. • For example, atoms with 13 protons are aluminum atoms. • Atoms with 29 protons are copper. • Protons and electrons have electric charges. • Protons are positive and electrons are negative. • Neutrons have no charge. • In most natural atoms, the number of protons equals the number of electrons. • The positive charges equal the negative charges. The atom, therefore, has no charge.

7. Electric current • In some atoms, the electrons are held tightly to the atom. In other atoms, some of the electrons are easily pulled away. They move from one atom to another. • Materials whose atoms give up some electrons easily are called conductors. • Materials that hold tightly to their electrons are called insulators. • In a conductor, electrons can move from one atom to another. • In an insulator, each atom’s electrons are tightly held, and electrons are not free to move between atoms.

8. electrons • Electrons can flow through a thin wire or a piece of solid material, or even through the air, as in a lightning bolt. • The flow of electrons is called current. • The measure of current flow is ampere or amp. • One amp is equal to about six billion electrons flowing past a point in one second.

9. electromotive • Electric current is the flow of electrons through a conductor. • When you want to move a chair, you have to push on it. You have to exert a force. In the same way, to get a current to flow, a force has to be applied. • This force, called an electromotive force, is measured in volts. • Without voltage, no current will flow.

10. battery • A battery provides electromotive force. • A battery has a positive terminal an a negative terminal. When the terminals are connected to the opposite ends of a wire, electrons start moving. • They are attracted to the positive terminal and repelled from the negative one. • This sets up a current, or flow of electrons.

11. Electrical current flow • Ohm’s Law is an equation that describes the flow of electrical current. • Current (amps) = Voltage _______________ Resistance (ohms) • If voltage gets larger, current gets larger. If resistance gets larger, current gets smaller.

12. resistance • Some conductors are better than others. • For a given voltage (force), more current flows through a good conductor than a poor one. • Resistance is the opposition to a flow of current. • It is the measure of how good a conductor is. • A material with high resistance is a poor conductor. • A material with low resistance is a good conductor. The unit of resistance is the ohm.

13. Electronic components and circuits • Electronic components, or parts, control the flow of electricity (electrical current). They carry out many useful tasks. • Components are connected together in different ways to form circuits. • A circuit is a group of components connected together to do a specific job. • Designers show plans for circuits using drawings called schematics. In these drawings, each component has its own symbol.

14. resistor • One of the simplest components is the resistor. • A resistor has a known resistance value. • It is used to control current flow. • Resistors come in a wide range of values, from less than one ohm to tens of millions of ohm. • On many resistors, color-coded bands indicate the resistance in ohms.

15. semiconductors • Semiconductors are materials that are neither good insulators or good conductors. • The most common semiconductor material is silicon. • One kind of component made using semiconductors is the diode. • A diode lets current flow in one direction but not the other.

16. transistor • One of the most important electronic components today is the transistor, which was invented in 1947. • A transistor is a resistor that lets a small amount of current control the flow of a much larger amount of current. • Transistors are used to control electric motors. They can also be used to control the storage of a small electric charge used to represent information, as in a computer. • The transistor is very small.

17. Other components • Other components are like transistors and resistors. • A thermistor has a resistance that changes with the temperature. • Thermistors can be used to make electronic thermometers. • They can also be used as part of the control system of refrigerators or ovens. • A photoresistor has a resistance that changes with the amount of light hitting it. • Photoresistors can be used to turn on lights when it gets dark. They also can be used to measure light.

18. Printed circuits, p. 96 • Circuits are groups of components connected together to do a specific job. • Components are often connected by wires. • Soldering is a method of joining two wires together. • A metal solder is melted on them, forming a connection. • Solder has low resistance and therefore makes a good connection.

19. Wires can’t touch! • Care is taken to make sure wires in a circuit do not accidentally touch. • This would set up an unintended flow of current (a short circuit). To prevent this, wires often have a covering of insulation. The insulation prevents short circuits. • Early circuits used large components that were connected to each other by several wires. • Each wire was soldered by hand. • Components became smaller over the years, and hard to solder. • Also, a way was needed to make the same circuit over again without mistakes…

20. Printed circuit board • The printed circuit board solved both problems. • A printed circuit board is a thin board made of an insulating material, such as fiberglass. • On one or both sides, a thin layer of a good conductor, often copper, is plated right on the board. • Patterns etched in the copper form paths for electricity. • Holes for mounting components are drilled in the board.

21. Cont’d… • The components are then soldered to the conducting paths on the board. • The conducting paths are photographically placed on the board, so many boards can be made with exactly the same circuit. • Once the components are mounted on the board, they can all be soldered at once by an automatic soldering machine.

22. Integrated circuits • One of the most important inventions of the twentieth century is the integrated circuit. • An integrated circuit provides a complete circuit on a tiny bit of semiconductor. • Integrated circuits are often less than one-tenth of an inch long by one-tenth of an inch wide. • This chip contains components and conducting paths.

23. Chip p. 97 • A chip is designed by an engineer, who makes a drawing of it several hundred times larger than it will be. • The drawing is photographically reduced, forming a mask. • The mask is used to put patterns on a wafer of semiconductor material. • Many identical circuits are made at once on a round wafer several inches across.

24. Computers… • Computers are built using large integrated circuits. • Computers that took up rooms of space twenty years ago now fit on a desk top or on a cell phone because of integrated circuits. • Chips have replaced large, bulky circuits in many other systems as well.

25. Analog and digital circuits • Information can be represented by electricity in several ways. • One way is to have a voltage change based on the information it represents. • A voltage could represent a person’s speech. • It would get larger as the person talked louder. • In this case, the voltage is the analog of, or similar to, the person’s speech. • It is called an analog special.

26. Analog circuit • An electronic circuit that works with analog signals is called an analog circuit. • Voltages in such a circuit change smoothly, as do the things they represent, such as a person’s voice. • Sometimes information must be very accurate or must be sent over long distances. • Under these conditions, analog circuits are not good enough… • In these cases, digital technology is used.

27. Digital circuits • In digital circuits, information is first coded into a series of 0s and 1s. • A voltage above a certain value is coded as a 1. • A voltage below that value is coded as a 0. • Each 1 or 0 is called a bit, short for binary digit. • Binary refers to the number system that has only two numbers, 0 and 1.

28. What is a computer system? • A computer does its work according to a list of instructions, called a program. • The program can be changed at any time. • A computer is therefore a general-purpose tool. • A programmer makes it do a given job by providing instructions, but can change the instructions to make it do a different job – this is called program control.

29. Computers today • Most of today’s computers are digital, using 1s and 0s to represent information. • Any number can be represented by a binary number, a group of 1s and 0s. • Bits are organized into groups of 8 to make them easier to work with. • These groups of 8 bits are called bytes. • Each byte can represent one of 256 different characters (numbers, letters, punctuation, or other information)

30. Data • Data can be represented by bytes, kilobytes (one kByte = one thousand bytes), or megabytes (one Mbyte = one million bytes) • So how many bytes would 4 kBytes represent?

31. The computer processor • All computers have some parts in common. • The first is the processor. • The processor controls the flow of data, its storage, and what the computer does with the data. • The processor reads the program and changes the instructions into actions. • The actions might be able to add two numbers or store a number or letter.

32. processor • The power of a processor refers to how fast it is. • Personal computers can carry out hundreds of thousands of instructions in a second. • Large business computers can carry out millions of instructions per second (MIPS). Very fast computers can handle hundreds of millions of instructions per second.

33. Memory p. 102 • The place where the program is stored is called the memory. • The memory also stores the information being worked on. • Most computers use integrated circuit memory circuits. • A tiny chip can store more than one million characters.