Digital Electronics

CMOS Circuits

"complementary metal oxide semiconductor", can operate at 3-15 volts, consumes far less power than a TTL, very static-sensitive, Soldering a CMOS circuit with an ungrounded soldering iron can destroy the IC

Op-Amp Circuits

"operational amplifier circuits", can be used as a comparator,

TTL Circuits

"transistor transistor logic", used because they are versatile and hard to damage, needs a precisely regulated 5-volt supply

Disadvantages of Pre-Etched Boards

- Changes to the circuit are difficult to make. - The circuit doesn't match the dimensions and layout of the final finished product, as it does when wire-wrapping techniques are used.

A flip-flop can store up to ___ bit(s) of inofmration

1

A clock runs at about 1 pulse per second, or at ____.

1 hertz

Steps to making a circuit board:

1. Hand-Drawn Silkscreen 2. circuit board made from a nonconducting material, such as epoxy-based fiberglass or resin 3. copper covering the entire base of the circuit board 4. silkscreen is laid over the bare copper-coated circuit board. 5. coating is then sprayed over the silkscreen 6. silkscreen is removed so that the pattern of the original artwork is duplicated on the bare board 7. Once the coating on the circuit board is dry, the board is dipped in a chemical etching solution. This solution removes everything not protected by the coating. 8. By using etching, an exact reproduction of the original artwork can be mass-produced.

Crystal-Controlled Oscillator

A crystal-controlled oscillator provides reliable high-speed timing pulses that can run in hundreds of millions of pulses per second.

Digital Mousetrap

A light shining onto an electric eye produces one of the comparator's input voltages. A potentiometer is used to set the point where the shadow, created by a mouse walking through the light beam, will change the comparator's output to high and set off the trap.

Push Button Switch

A single pulse is sometimes required to activate a digital device. One example is the push-button switch you use to turn on your computer. When you push the button, a single pulse connects your computer with electric power. Digital devices are capable of extremely fast operations. Sometimes problems occur because the push button doesn't open or close cleanly with just one pulse. Instead, it bounces and produces many pulses. This confuses the digital circuit. Confused circuits don't perform efficiently.

The 555

A timing circuit that continues to function despite interruptions is the 555. This circuit also can be purchased already made. The 555 integrated circuit can deliver timing pulses as slowly as one pulse every few days, or as frequently as hundreds of thousands of pulses per second. Two resistors and a capacitor determine the oscillation frequency of the 555. The two resistors function as a voltage divider, allowing the circuit to function at a constant frequency despite changes in supply voltage or temperature.

Computer Technology

Advances in computer technology allow information to travel across the world in a matter of seconds.

Up Counter

An up counter might be used in a: Clock Stopwatch Car odometer

pre-etched circuit

Another semi-permanent prototyping technique, designed on a solderless breadboard, transferred to the pre-etched board, and then soldered into place

Debouncing Waves

Computers are much faster at capturing input data than humans. Our eyes can barely detect the flashing of a fluorescent light operating at 60 flashes per second. But modern computers are many millions of times faster. When we flip a simple switch, we hear only one "click", but a computer will "see" the internal switch contacts vibrating many times before the contacts come to rest. This difference between what we are trying to "tell" the computer and what the computer "hears" can cause serious computer processing problems. Your computer keyboard is a perfect example of this problem. When you type the letter "a", for example, you want to input one and only one "a" into the computer. A normal mechanical switch found under the letter "a" on your keyboard will send many "a's" to your computer before it comes to rest after you type it. To solve this problem, switches need to get rid of the extra vibrations every time they are used. This process is called switch "debouncing." A counter will consider each bounce pulse separately and count them. Thus one up-down switch operation can produce a count of anywhere between 1 to perhaps 5 to 10 or more when connected to a flip-flop counter trigger input. Four different switch-debouncing circuits are tested, and you will note that they are equally effective in eliminating switch contact bounce.

Faster clocks must contain a _______________________ to provide such precise high-speeds.

Crystal-controlled oscillator

A NAND gate can be used to make a ______________ logic circuit.

Digital

Down Counter

Down counters are useful in a: TV quiz show Rocket launch Kitchen timer

Early Transistors

Each transistor was a separately etched circuit enclosed in its own metal can. Several transistors were needed to make a logic gate, but at least they required far less power and space.

Early ICs

Early integrated circuits combined several transistors on a single chip. Logic gates could be manufactured into a single package. At the same time, printed circuit boards were the most popular construction technique.

Flip-Flop Circuit

Flip-flops can be used for computer memory. Flip-flops can also be used to make digital counters. A digital counter is needed for a computer to perform math computations. Counters are also needed to allow a computer to perform tasks in a certain order, or sequence. Counters therefore, in combination with computer memory, form the heart of sequential logic. The flip-flop (or one bit memory) was described in an earlier activity (NAND Flip-Flop). The circuit of the flip-flop using two NAND gates is shown in Figure 1 and it is called a RS Flip-Flop. Also shown is the standard symbol for the RS Flip Flop. A binary 0 fed to S sets the flip-flop, and a 0 fed to R resets it. A flip-flop with R and S inputs requires two input "active low" signals, one for SET (S), the second for RESET (R). This requirement specifies normally "high" inputs with "active low" inputs, and where both inputs are "low" simultaneously, the output is indeterminate. A Triggered flip-flop has a Trigger (T) or clock input. It can also have J-K or D inputs as shown by the various flip-flop symbols in Figure 2. The triggered flip-flop is used for the counters in this activity. When a binary input is applied to the T input of a flip-flop, the outputs, Q and Q, will change states when the T input goes from 1 to 0. This is referred to as "negative edge triggering". The next T input will cause the Q and Q states to reverse again. This is useful in counting as shown in TABLE 1. Refer to Table 1 and observe that the 2-bit changes every time the 1-bit changes from 1 to 0. Also, the 4-bit changes every time the 2-bit changes from 1 to 0. The 8-bit changes every time the 4-bit changes from 1 to 0. These changes are indicated by the arrows. This is the function of the triggered flip-flop. The output changes each time the input changes from 1 to 0. A binary counter, therefore, consists of a series of connected triggered flip-flops, as shown in Figure 3, where the Q from one flip-flop is connected to the T from the next "higher order" flip-flop. The arrow at the T input denotes that the input is edge "triggered" (going from one level to another). The circle at the T input denotes that the input is triggered when the level is going in the negative direction as required for counting.

One Input High

However, if the other output is high, the clock pulses appear at the NAND gate's output. The red arrow shows the pulses. The green arrow shows the output.

Timing Device

If you're designing a simple timing device, you need to think about which basic components are required for the device to perform its function. This is a diagram of a digital stopwatch. To design one, you would need three input switches: One to clear the watch to zero One to start timing One to stop timing

Nonconducting Channel

In order to accommodate ICs, all solderless breadboards have a series of horizontally connected holes (usually five) arranged along each side of a central nonconducting channel. Each pin on the IC is separated by one tenth of an inch. The rows of pins on the right and left are separated by three tenths of an inch.

Breadboard

In the early days of Electronics, electrical engineers would take a wooden breadboard and partially hammer brass nails into it in a grid pattern. They could then wrap wires around the nails and easily build circuits to test. The rest of the circuit is built by placing components and connecting them together with jumper wires. Then when a path is formed by wires and components from the positive supply node to the negative supply node, we can turn on the power and current flows through the path and the circuit comes alive. For chips with many legs (ICs), place them in the middle of the board so that half of the legs are on one side of the middle line and half are on the other side.

Internal Clock Pulses

In this way, the NAND gate controls the pulses from the internal clock.

Two ____________ gates can be used to create one flip-flop.

NAND

You could use a simple ... to control the timing pulses coming from the internal clock.

NAND gate

Computer Speed

Often, the speed of a computer is referred to by how many bytes it can process per second. You've probably heard of kilobytes, megabytes, and gigabytes. This table shows the common prefixes, their abbreviations, and their sizes.

Reliability

People rely on an integrated circuit to function, no matter what kind of interruptions in service may occur. If there is a dramatic weather change, or a brief power outage, the circuit needs to keep functioning normally.

Printed Circuit Boards

Printed circuit boards can be mass produced rapidly and easily using robotics technology. They're inexpensive and extremely durable. In addition, they can be easily tested.

Debouncing

Push-button switches need to be debounced to avoid the problem of bouncing pulses. To debounce a switch, the circuit is attached to a push button, which fires when it detects the first vibration. The circuit remains on while the rest of the vibrations go by. This is called a one-shot circuit because it produces one output pulse despite a lot of input noise.

All of the following are true of Vacuum Tubes, EXCEPT:

Similar function to today's household vacuums

Circuit Testing

Solderless breadboards usually have two vertically connected columns of holes between each regular breadboard section. This makes circuit testing easier, since the positive and ground connections are very accessible. However, solderless breadboards are usually too bulky and expensive for a final design.

One input Low

The NAND gate controls the functions as follows. If the clock pulses are applied to one of the inputs of a NAND gate, and the other input is low, no clock pulses can pass through the NAND gate's output.

All of the following are true of breadboards, EXCEPT:

The ability to handle 1 million or more circuits.

Control Circuit

The control circuit controls the pulses coming from the internal timing clock that are being sent to the counters.

Internal Clock

The simple flip-flop circuit can be modified to vibrate automatically between high and low states. To slow the vibration down, various items can be added, such as: Timing components Resistors Capacitors

SPDT Switches

The start and stop switches need to: - Bring the control input of the NAND gate to "high" to start the counters - Bring the control input of the NAND gate to "low" to stop the count Adding a single pole double throw switch, or SPDT, can do this. The SPDT acts as an on-off toggle switch to start and stop the timing device.

Switches

The type of switches required to start and stop the timing device depends on the control circuit design.

Types of Logic Gates

There are three basic types of logic gates: AND gate OR gate NOT gate

Toggle Switches

Two push-button switches that implement the same toggle function

Wire Wrap

Wire wrapping techniques on perf board are more commonly used for a final design. A special wire wrapping tool is used to connect the pins of the IC together. The ICs are mounted in special wire wrapping sockets.

Speed & Performance

You've learned that internal clocks on digital devices can operate at different speeds to perform a desired function. A clock runs at 1 pulse per second, or 1 Hz (hertz). This is slow compared to a communications satellite that runs in gigahertz, or billions of pulses per second.

Node

a point in a circuit where two components are connected. On the breadboard, a node is the row of holes that are connected by the strip of metal underneath.

Comparator

a simple analog-to-digital converter, can be used in a digital thermostat, can be used to design a digital mousetrap, compares the input voltage at each of its two inputs, If voltage one is less than voltage two, the circuit's output is low, or off. If voltage one becomes greater than voltage two, the output signal is high, or on.

Electrical Technicians

can construct a wire-wrapped circuit to match the schematic produced by an electrical engineer

What controls the pulses of the internal timing clock of a stopwatch?

control circuit

Combining the flip-flop and the NAND control gate allows you to ...

control the clock timing pulses

Electronic Draftsperson

designs circuit board layouts with sophisticated CAD programs used to design circuits

Vacuum Tubes

large and heavy, required tremendous amounts of power to run, the framework parts (chassis), were constructed from heavy-duty aluminum and insulated with point-to-point wiring connectors

Silkscreen

made from the draft person's original artwork in order to transfer the design to the circuit board, silkscreen is laid over the bare copper-coated circuit board. A coating is then sprayed over the silkscreen. The same silkscreen can be used repeatedly.

A(n) ______ is the internal timing device in a computer.

oscillator

Switches are used to...

start and stop the timing count

Etching

the board is dipped in a chemical solution that removes everything not protected by the coating

Prototyping

the building of one or two parts to make sure that everything operates as specified. Once the prototypes are correct, the mass production of the parts can begin.

The type of switch required to start and stop a timing device depends on...

the control circuit design

To design a digital stopwatch, what components do you need?

three input switches

Early integrated circuits combined several __________________ on a single chip.

transistors

555 IC (integrated circuit) belongs to the linear-integrated circuit family.

true

Although the transistor was invented in 1947, it wasn't until the 1950s that semiconductors took over in digital circuit construction.

true

Connections between different components are formed by putting their legs in a common node.

true

Digital circuits now could be assembled on perforated boards with point-to-point wiring, or on printed circuits.

true

For the last 40 years, custom-designed printed circuit boards have been the main construction method for mass-produced items.

true

Holes on the breadboard are located about one tenth of an inch apart to accommodate the spacing of integrated circuit pins.

true

If the control input is set to low, the output of the NAND gate will stay high and will not allow the timing pulses to pass through.

true

In addition, some breadboards are available with built-in power supplies and timing clocks.

true

In the 1940s, in the first digital computers, vacuum tubes were used in logic gates.

true

Lightweight construction practices led to digital circuits that required just a few square inches of space.

true

Linear circuits ONLY process analog signals.

true

Linear ciruits DON'T process a digital signal.

true

Solderless breadboards come in a variety of sizes that will handle anywhere from a few to hundreds of integrated circuits.

true

The flip-flop arrangement is ideal for controlling the timing pulses in a digital stopwatch.

true

The push buttons need to be connected to the set and reset inputs of the simple flip-flop

true

The system clock controls the speed.

true

The timing pulses can be added to one of the NAND gate's inputs.

true

Today, hundreds and millions of transistors can be manufactured in a single IC.

true

Transistors today are made at the molecular level. Circuits are still mass produced on printed circuit boards.

true

NAND gates can ...

turn a stream of pulses on or off.

Which number represents a switch's on position?

1

Versatility

Flip-flops are quite versatile. You can add a trigger or clock input to divide incoming clock pulses. If you combine these flip-flops in a series, the incoming clock pulses can be divided into any number you choose. Flip-flops used in this way can make digital counters.

IBM Corporation

IBM Corporation delivered its first computer in 1953. Even by 1956, fewer than 150 of these large mainframe computers existed. However, during the 1950s several items were being developed that would allow the next great leap in computer technology.

Water Clock

Sir Isaac Newton invented a water clock to measure the speed and acceleration of objects in his experiments. The clock counted the number of drops that dripped into a container.

BCD

Unfortunately, most common integrated circuits used to make visual displays, like those on a watch or calculator, are limited to 4 bits and can't handle a 7-bit number. Therefore, you need to encode each decimal place value separately as a 4-bit binary number. This is called binary-coded decimal encoding, or BCD for short.

A logic gate is the internal timing device of a computer.

false

A Computer Repair Technician takes care of hardware problems.

true

A flip-flop circuit is one of the simplest kinds of memory.

true

A floppy disc is a peripheral device.

true

A truth table shows how inputs and outputs relate to each other.

true

The most common integrated circuits (ICs) contain up to four inputs

true

The most commonly used output device is the printer.

true

The Maya in southern Mexico created an extremely accurate calendar that divided the year into ... periods of ... days each. They added ... more days at the end of the year to total 365 days.

18 periods, 20 days, 5 more days

Charles Babbage

A British mathematician and inventor named Charles Babbage first envisioned the programmable calculator. In the mid-1800s, the only power available to Babbage was steam. He spent years trying to develop a working model without ever succeeding.

Flip-Flop Memory

A flip-flop circuit remembers whether something is supposed to be on or off. The circuit has two inputs and can keep its output stable, in either a high or a low state. Momentarily forcing one of the inputs low, while keeping the other input high, causes the flip-flop to output a steady high signal.

NAND Gate

Another type of useful logic gate that you can buy combines the functions of an AND gate and an inverter. It's called a NAND (for NOT + AND). You can use this single type of logic gate to make any kind of digital logic circuit you need. See how its schematic symbol combines the AND symbol and the small circle that represents the NOT gate function. A NAND gate might be used inside the circuitry of a rocket launching system. Let's say that a certain level of wind conditions, temperature, fuel pressure, and electric current all need to be present for the automatic launch to take place. If any of these parameters are outside the correct limits, the NAND gate will stop the launch. Therefore, the wind can't be too strong, the temperature can't be too low, and the fuel pressure or the electric current can't deviate from the set levels.

Computers contain four types of hardware components:

Computer processor Input devices Output devices Secondary storage devices

____ are stored using on and off pulses within a code.

Digital signals

Digital Signals

Digital signals differ from analog signals; they do not change smoothly. The accuracy of a digital device depends on how fast the signal is changing and how often sample measurements are made. The frequency of measurement depends on the information needed. If you sampled the temperature outside with a thermometer every five minutes, the reading would be much more accurate than if you sampled it every three hours. Yet, obviously, you wouldn't need to sample the temperature 10,000 times a second. Digital signals are stored using a series of on and off pulses within a code.

Hardware

Electromechanical devices contain electronic and mechanical parts known as hardware. Hardware refers to devices that enter, process, store, and retrieve information.

Examples of peripherals are:

External hard drives to store information Ethernet routers to transmit information between computers Printers to produce legible hard copies

Flip Flops

Flip-Flop is the unusual name given to a two-state device which offers basic memory for a sequential logic circuit. Flip flops are used for the storage of binary numerical data. The circuit can be made to change state by signals applied to J and/or K inputs and will have one or two outputs. A common type of flip flop is the "jk flip flop". It is the most versatile of the basic flip flops. It operates under the principal that if both J and K are different, then Q takes on the value of J. If J and K are both low, then no change occurs. Escalators are among the many applications for flip-flops. One of the inputs can be connected to a push button labeled "on." The other input can be connected to a push button labeled "off." When the on switch is pushed, the flip-flop will output an on, or high, signal. The escalator will run until the button connected to the off input is pushed. The flip-flop will then assume a low state, and the escalator will remain off until someone pushes the on switch. You can construct a simple flip-flop by wiring two inverters together, as shown in this diagram. You learned how NAND gates can be used as inverters. So now you can make a flip-flop using two NAND gates. A flip-flop remembers, or stores, one bit of information. If you combine flip-flops, you can store more bits. Because these circuits are so useful, you can buy them already made in an integrated circuit. Flip-flops are also called shift registers, memory registers, or latches.

Herman Hollerith

In 1896, the American inventor Herman Hollerith created a company that expanded on Babbage's invention. The company tabulated results and information on punch cards. By this time, electricity had appeared in U.S. cities. Therefore, Hollerith's machines could run on electric motors and relays.

Squaring Values

In binary numbers, each number place, or bit, is worth twice as much as the one before it. For example, the first place is worth either 0 or 1. The second place is worth twice as much, either 0 (2 x 0 = 0) or 2 (2 x 1 =2). The third bit is worth twice as much as the second bit, either 0 (2 x 0 = 0) or 4 (2 x 2 = 4). The process of adding bits can be repeated as often as you wish to create the numbers to suit your application. Study this 4-bit binary table so that you can write your own codes.

ENIAC (Electronic Numerical Integrator And Computer)

In the 1920s, the development of the vacuum tube led to the creation of the first true digital computer. In the mid-1940s, ENIAC was built at the University of Pennsylvania as part of a secret military project called Project X. The computer was 150 feet wide and was made from 17,468 vacuum tubes. It used enough power to run 2,000 of todays computers, could do 5,000 addition computations in a second, but is 100,000 times slower than the modern pc.

Input & Output

Input and output devices move data into and out of memory. The computer terminal keyboard is the most common input device. Disc drives are also input devices.

Integrated Circuts

Integrated circuits led to the creation of the first minicomputers. These computers were small enough to install almost anywhere, including in the average home. Minicomputers paved the way for the personal computer. Advances in the design and construction of integrated circuits allowed more components to be placed on a single chip.

Microprocessors

Intel Corporation invented the first microprocessor in the early 1970s. Many other companies used this technology to produce personal computers. Over the next 10 years, 25 million personal computers were sold in the United States alone!

Combinational Logic

Logic gates can be combined to solve more complex problems and to create new types of digital logic gates. This important process is called combinational logic, or equivalent logic, because the combination of logic gates equals the function of other logic gates. For example, engineers examining a circuit diagram might determine that they can use equivalent logic to simplify a circuit by using fewer parts to perform the same function.

Memory & Feedback

Memory relies on feedback. This means that the output of a gate is fed back into the input. The simplest type of circuit memory is a flip-flop circuit. A flip-flop is a circuit constructed using gates and, typically, two inverters.

Analog Signals

Microprocessors use two types of signals: analog and digital. In an analog signal, the information can vary over a continuous range of values. A mercury thermometer is a good example of an analog device. As the temperature rises and falls, the mercury moves smoothly up and down the tube.

Computational Devices

More than 2,000 years ago, ancient people manipulated beads on an abacus to perform basic arithmetical functions.

A(n) ___ gate's output is high if any or all of its inputs are high.

OR

Transistor

Prior to the 1950s, computers used vacuum tubes. Then Bell Laboratories invented the transistor. Transistors were smaller, lighter, and used far less power than vacuum tubes. They also cost less to produce. By the end of the century, entire circuits containing transistors, resistors, and capacitors could be manufactured on a single chip called an integrated circuit.

Punch Cards

Punch cards stored and calculated information that could be read and sorted by a machine, rather than by humans. For the first time, people could write programs on punch cards, which allowed customized machines to perform specific tasks. Thanks to punch cards, machines could now be programmed to perform tasks that previously had to be done by humans. Punch cards ruled the information and computation industries for more than 50 years. They led the way to modern computers.

Binary Encoding

Remember that the sum of the bit values equals the decimal number. We would need 7 bits to encode the number 80 for our thermostat. Look at the chart to help you understand why. You can see that the binary number for 80 is 1010000, or 64 + 16. This is called binary encoding. The amplitude of signals on a music CD are encoded this way.

Polarity

Reversing the polarity of the input signals causes the flip-flop to output a steady low signal.

Common Circuits

Some circuits are so commonly used that you can buy them already made. This saves you the time of having to build them from separate logic gates. An example is an EXCLUSIVE OR logic gate.

Secondary Storage

Storing data in primary memory is expensive. In addition, data stored here is easily lost when the computer's power source is turned off. Most data and software programs are kept in secondary storage until needed, even though it may be slower to retrieve. A common secondary storage media remote hard drives located in a central location. This is often referred to as CLOUD STORAGE

OR Gate

The basic concept is that if A or B, or both A and B, are 1, then the output will be 1. Like an AND gate, an OR gate can have two or more inputs. The important difference is that an AND gate's output is high only if all inputs are high. An OR gate's output is high if any or all of its inputs are high.

Binary Number System

The binary number system is effectively used with digital devices, since all possible numbers can be represented as a series of zeroes and ones. Zero means that the circuit is off (also called low). One means that the circuit is on (also called high). Computers use binary digits in place of decimal digits. Where decimals have ten possible values ranging from 0 to 9, bits have only two values: 0 or 1. This makes computer operations much easier to design. The size of the binary number required to do a particular job depends on the range of values of the information to be digitized. Each 0 or 1 is called a bit, which stands for "Binary digIT."

1st Calculator

The first calculator appeared about 300 years ago. Since it required precision gears, it couldn't be manufactured in large quantities. In the 1800s, however, the Industrial Revolution ushered in mass production.

Digital Signal Factors

The first factor is how often the sample is taken. The number of readings depends on what you wish to measure. A thermometer gives an accurate reading if the temperature is sampled every five minutes. The second factor that affects the accuracy of the digital signal is how carefully the value of the signal is measured. Let's review the example of the digital thermometer again.

XOR Gate

The idea behind the EXCLUSIVE OR or XOR gate is that if input A or input B, but not both, are 1, then the output is 1. Interestingly, if all the inputs are 1, or if all the inputs are 0, then, and only then, will the output be low. Here's an example. To make a unanimous vote detector that will indicate when all voters agree to vote for or against some issue, an XOR gate can be used, followed by a NOT gate. This combinational logic gate is called an Exclusive NOR gate (for Exclusive OR and NOT). Like other useful combinational logic circuits, this circuit can be purchased already made in integrated circuit form.

Music Sampling

The issue lies in the fact that analog music is recorded as a steady stream where all the highs and lows are captured. In a digital recording, samples are taken that may exclude a particular high or low. Audiophiles (people who live and breath music) feel that digital recording does not truly reflect the music that the artist is trying to make. While digital music may sound "cleaner" than analog, it may be that the artist was going for more of a "grittier"effect.

Precision Timing

The timing device of any internal clock must be carefully controlled. The last seven minutes of the successful landing of the Mars Rover Curiousity highlight the importance of very precise timing. For the last seven minutes of the flight computers controlled each step of the landing.

AND Gate

This is a diagram of the AND logic gate. It has two or more inputs and one output. The idea is that if both input A and input B are the same--1, let's say--then the output will be 1. Remember that this logic gate is named AND because the output is only "on," or 1, when each and every input is "on," or 1. The information goes into the inputs. The logic gate sends the processed result to the output.

Decimal to Binary

This situation could be written mathematically as ON = > 80 degrees. Of course, digital circuits can deal only with ones and zeroes. Therefore, we need to change the decimal 80 degrees to its binary equivalent.

Circuit Speed

Today's machines are much faster than machines created 10 years ago. An early 8-bit (per byte) machine running at 8 megahertz (8 million bytes per second) could process 2,048,000,000 different values per second. Common 32-bit machines can handle over 2 quadrillion different values per second. Today's more advanced 64-bit machines are capable of processing far more data at a faster, more efficient rate.

Thermometer Range of Values

We could devise a thermometer that measures only every 10 degrees. Let's say that the range of temperatures falls within 0 and 120 degrees Fahrenheit. This thermometer would have 13 values. The problem is that we wouldn't know if the temperature were 81 or 89 degrees. So the reading wouldn't be a very accurate. To produce a more accurate thermometer requires more values. To make the thermometer accurate to 1 degree requires 121 values, from 0 to 120. The more carefully a digital device measures a signal, the more accurate the result is.

Digital Signal Advantages

When signals change at fast rates, the advantage of digital equipment is obvious. Our eyes can sense changes up to 30 times per second. Our ears can detect changes up to 20,000 times per second. Our eyes and ears can't decipher changes in signals that are faster than either of these. Instead, such signals must be recorded and played back in slow motion--or else sampled at a rate slow enough for us to keep up.

Truth Table

When you perform an experiment, you need to record your data in an orderly way. Similarly, a truth table shows the true relationships between the inputs and their resulting outputs. This example shows that when there are two inputs, there are four possible combinations of input switch positions. For the two-input AND logic gate shown here, the output is 1 only when both inputs are 1.

Control Timing

You can control the timing device to perform the desired function by using a flip-flop and a NAND control gate. Look at the diagrams to see how this works.

Common Integrated Circuits (ICs)

You can increase the number of available inputs by placing the logic gates in a series. The diagram shows a seven-input AND gate configuration. You can see that there are two logic gates, one with four inputs in a series and one with three, to make a total of seven. All seven inputs would need to be 1 to make an output of 1.

Digital Clock Voltage

You can make a digital clock by using counters. These counters can divide the 60 cycles per second present in the AC line voltage available from a regular wall outlet. You can start by dividing the 60 cycles per second by 60, which will yield one pulse per second. If the one pulse per second that we just created were divided by 60 again, we would produce one pulse per minute. By dividing the one pulse per minute by 60, we could produce one pulse per hour. By counting and displaying the second, minute, and hour pulses, you would create a clock! This is the premise on which digital clocks are designed.

Internal Timing

You learned how digital counters can be used to create a timing device, or clock, that runs from the 60 Hz time base found on normal line voltage. Since computers need to run at frequencies much faster than 60 Hz, they need their own internal frequency-generating device, called a clock or oscillator. Computer clocks run at hundreds of millions of pulses per second.

Clock Rate

You learned that the binary sequence 0001 references the number 1 and that 0010 references the number 2 and so on. We also know that zeros (0) and ones (1) form the basis for all computer operations. The speed of a computer processor, or CPU (central processing units), is determined by the clock cycle or rate which is the frequency of one cycle of the clock. In general terms the higher number of cycles per second, the faster the computer microprocessor will be able to process information. The clock speed is measured in Hz, typically megahertz (MHz) or gigahertz (GHz). For example, a 4GHz processor performs 4,000,000,000 clock cycles per second. That means that for every second, 4 billion changes between 1 and 0 can occur. In the late 1970s CPU clock speeds for early Apple, Atari and Commodore computers were at 1 MHz (1,000,000 cycles per second). In 2015 President Obama signed an executive order for the US to build the world's fastest supercomputer by 2025. It will be capable of making one quintillion (a billion billion) calculations per second - a figure which is known as one exaflop.

Flip-Flops are also called

all the answers

A(n) ______ would use BCD encoding.

computer programmer

Ergonometric engineers mostly write code for digital circuits.

false

IBM invented the transistor, revolutionizing digital electronics.

false

UNIVAC was the name of the first digital computer.

false

Which of the following examples best describes the workings of a NOT logic gate?

garages

Inverters

it is best used in combination with other logic gates. A NOT logic gate is inserted into a circuit to prevent an action from taking place. A good example is the safety circuit on a garage door. If the door encounters an obstacle while being lowered, an increase in the electric current is detected. The NOT gate then prevents the door from closing.

How many outputs will be produced if only one input goes into one OR gate?

one

_____ were Herman Hollerith's technological breakthrough. They allowed programs to be written to control a machine.

punch cards

The accuracy of _________________ may affect how carefully the value of a digital signal is measured.

sampling

The number of functions that a digital circuit can perform in one second depends mostly on the ____.

system clock

A kitchen timer is an example of a down counter.

true

Agricultural societies needed to plant and harvest crops, hunt for food, and keep track of changes in weather.

true

Analog signals are measured over a smooth, continuous range of values.

true

Charles Babbage tried to make programmable calculators that ran on steam.

true

Digital circuits use logic to compare values and make decisions.

true

Digital signals are NOT exact copies of the original signal.

true

Each zero or one in a digital signal is a bit.

true

If the input is 1, the output will be 0. If the input is 0, the output will be 1.

true

In the binary number system, either 1 or 2 represents all numbers.

true

In the last 50 years, the lives of average people have changed dramatically due to rapid advances in technology.

true

The number of functions that a digital circuit can perform depends on the speed at which the circuit is running.

true

The purpose of some of the first devices invented was to keep track of time.

true

Today, microprocessors are found in many everyday consumer products, such as TVs, digital cameras, cell phones, cash registers, cars and trucks, and musical instruments. Many new jobs, such as Network Technician and Systems Engineer, have been created to support these devices.

true

Bits & Bytes

1 byte = 8 bits 8-bit bytes can handle 256 values. 16-bit bytes can handle 65,536 values. 32-bit bytes can handle 4,294,967,296 values. Early personal computers handled only 8-bit bytes.

The computer processor has two main parts:

1. Primary memory provides temporary storage for the data being processed, as well as software programs. 2. The central processing unit (CPU) contains the electronic circuits that process all the data in the computer. A key component of the CPU is the internal clock inside the CPU which controls how software programs operate. You will learn more about clocks and clock speed later in this module.

Memory Device

A MEMORY device or circuit "remembers" a previous input (switch position) even after the input has been changed. A simple memory circuit consists of two NOTs or INVERTERS wired as shown in Figure 1. A memory device remembers a switch position even after the input has been changed. If you arrange the gates in the correct way, they will remember an input value and allow you to create a variety of useful circuits.

Analog to Digital Conversion

Analog-to-digital conversion is the process of changing analog information into a binary number for use by a digital device. Integrated circuits can be designed to function as an analog-to-digital converter, or A-to-D converter for short. The size of the A-to-D converter is equal to the number of bits required for the job. A 4-bit binary number would need a 4-bit A-to-D converter.

Logic gates can be used to create?

memory

UNIVAC (Universal Automatic Computer)

In the mid-1950s, the creators of ENIAC built a general-purpose computer for science and industry called the UNIVAC. UNIVAC cost about one million dollars to build.

Logic Gate

A logic gate is a device that processes information in a circuit. Logic gates take information from the input and send the processed result to the output. Logic gates can compare values, perform arithmetic, or sequence and store information. These symbols assist Electrical Engineers who design digital circuits. Logic gates are used to make decisions and solve problems. The number of combinations of inputs depends on the number of input gates, as shown in this table. No matter how many inputs an AND logic gate has, there is only one combination of inputs that allows the output to be a 1, or "on".

Computer Programmers

Computer Programmers code and decode information as a primary part of their job. To encode the number 80, you would first encode the one position. (This is 0 for the number 80.) You then encode the ten position. (This is 8 for the number 80.) This requires two 4-bit binary numbers. The result is the number 1000 0000.

Binary Coding

Computers process numbers much more easily than words. For this reason, coding consists of simple commands and binary numbers. For example, suppose you need to design a thermostat to turn on the air conditioner when the room temperature rises above 80 degrees.

Digital to Analog

Digital circuits can change digital signals back into analog signals using a digital-to-analog converter. These devices are used in CD players. Digital circuits can also use logic to compare values and make decisions, calculate computations, or sequence events. Not long ago, only humans could do these tasks.

Potentionmeter

Digital circuits can change digital signals back into analog signals using a digital-to-analog converter. These devices are used in CD players. Digital circuits can also use logic to compare values and make decisions, calculate computations, or sequence events. Not long ago, only humans could do these tasks.

Digital Counter

Digital counters also can be purchased already made in an integrated circuit. Many can be preprogrammed to count either up or down. You can buy the counters to count in binary mode or in binary-coded decimal mode.

NOT Gate

It takes one bit as input and produces the opposite as output. This type of logic gate was named NOT because the output is not equal to the input. The NOT logic gate is also called an inverter. The inverter has only one input and one output. Whatever the state of the inverter's input, the output will be opposite.