D.E. Activities
ACtivity 1.1.3 - Scientific And Engineering Notation
In electronics, we frequently work with very small and very large numbers. For example, the propagation delay (i.e., the time it takes for the output to change after the input has changed) for a standard digital logic gate is 0.0000000095 seconds. Moreover, the clock speed of a typical personal computer is 2400000000 Hz. Working with numbers of this magnitude, both large and small, can be cumbersome and prone to error. For this reason we use a power-of-ten notation. With a power-of-ten notation, any number, no matter how large or small, can be expressed as a decimal number multiplied by a power-of-ten.
Scientific and engineering notations are the two most common forms of power-of-ten notation. In the field of electronics, engineering notation is the preferred notation because of the direct mapping between its powers and the International System of Units (the International System of Units is abbreviated SI from the French Système International d'Unités). The SI system is the modern form of the metric system. It is the world's most widely used system of units for science and engineering.
In this activity you will learn how to express numbers in scientific and engineering notation as well as the appropriate SI prefix.
Scientific and engineering notations are the two most common forms of power-of-ten notation. In the field of electronics, engineering notation is the preferred notation because of the direct mapping between its powers and the International System of Units (the International System of Units is abbreviated SI from the French Système International d'Unités). The SI system is the modern form of the metric system. It is the world's most widely used system of units for science and engineering.
In this activity you will learn how to express numbers in scientific and engineering notation as well as the appropriate SI prefix.
Activity 1.1.4 - Component identification
In the field of electronics, there are an endless number of different types of components. The ability to identify these components and to understand how they are labeled is an essential skill for anyone working in the field.
In this activity you will identify and determine the nominal values for a series of resistors and capacitors. We will concentrate on resistors and capacitors because they are part of virtually every electronics design ever made.
In this activity you will identify and determine the nominal values for a series of resistors and capacitors. We will concentrate on resistors and capacitors because they are part of virtually every electronics design ever made.
Activity 1.1.5a - Circuit theory: hand Calculations
Have you ever used a calculator to add some numbers, looked at the answer, and realized that it was wrong? How did you know that the answer was incorrect? The calculator gave you an answer; why did you not trust it? You knew the answer was wrong because you understand the fundamentals of mathematics. Your instinct told you that the answer could not be correct.
The same is true for circuit analysis. Throughout this course you will be using Circuit Design Software (CDS) to test the circuits that you design. This software will always give an answer, whether it is right or wrong. The only way that you will be able to rely on these answers is if you have an understanding of the laws of circuit analysis. You must develop the same instinct for circuit behavior that you have for mathematics.
In this activity you will gain experience applying Ohm’s Law and Kirchhoff’s Voltage and Current Laws to solve simple series and parallel circuits.
The same is true for circuit analysis. Throughout this course you will be using Circuit Design Software (CDS) to test the circuits that you design. This software will always give an answer, whether it is right or wrong. The only way that you will be able to rely on these answers is if you have an understanding of the laws of circuit analysis. You must develop the same instinct for circuit behavior that you have for mathematics.
In this activity you will gain experience applying Ohm’s Law and Kirchhoff’s Voltage and Current Laws to solve simple series and parallel circuits.
Activity 1.1.5b
As much fun as it is to analyze circuits by hand, the process becomes tedious as circuits grow in size and complexity. This is where Circuit Design Software (CDS) comes to the rescue. As the name implies, the CDS is a software tool that can be used to enter and simulate analog and digital circuit designs.
As with most computer applications, the CDS handles the mundane and repetitive tasks associated with analyzing circuits, allowing the designer (you) to concentrate on producing quality and creative designs.
In this activity you will gain experience using the Circuit Design Software to analyze simple analog circuits. In future activities we will use the CDS to analyze digital circuits as well. The circuits analyzed are some of the same circuits that were analyzed by hand in Activity 1.1.5a. Thus, the theoretical and simulation results can be compared.
As with most computer applications, the CDS handles the mundane and repetitive tasks associated with analyzing circuits, allowing the designer (you) to concentrate on producing quality and creative designs.
In this activity you will gain experience using the Circuit Design Software to analyze simple analog circuits. In future activities we will use the CDS to analyze digital circuits as well. The circuits analyzed are some of the same circuits that were analyzed by hand in Activity 1.1.5a. Thus, the theoretical and simulation results can be compared.
Activity 1.1.5c
Breadboarding is an essential skill for anyone who plans to design analog and/or digital circuits.
In this activity you will gain experience using a breadboard to build and test simple analog circuits. In future activities we will breadboard digital circuits as well.
The circuits analyzed in this activity are some of the same circuits that were analyzed by hand in Activity 1.1.5a and simulated in Activity 1.1.5b. This will allow you to compare the theoretical, simulated, and measured values.
In this activity you will gain experience using a breadboard to build and test simple analog circuits. In future activities we will breadboard digital circuits as well.
The circuits analyzed in this activity are some of the same circuits that were analyzed by hand in Activity 1.1.5a and simulated in Activity 1.1.5b. This will allow you to compare the theoretical, simulated, and measured values.
Activity 1.1.6
In this activity you will investigate both combinational and sequential logic gates. You will be asked to simulate simple circuits using basic logic gates. You will then complete a truth table for each logic gate based on the outputs generated from your simulation. The name of many of the fundamental logic gates in digital electronics are based on the logic output from the gate. From analysis of a truth table, could you determine the name and understand function of the gate?
You will examine the basic building block of sequential logic: the flip-flop. The investigation will conclude with a look at the 555 IC and how it is used to trigger events in a circuit.
You will examine the basic building block of sequential logic: the flip-flop. The investigation will conclude with a look at the 555 IC and how it is used to trigger events in a circuit.
Activity 1.1.7
Who fought in the Battle of Hastings in 1066? Who invented Silly Putty? Which of the Wright brothers flew first? All very important questions, but it would simply be impossible to keep all of the answers to such questions in your head. This is why we turn to the available resources like the Internet and textbooks to retrieve such information when necessary.
The same information overload is true when it comes to integrated circuits. What is the function of a MAN6760? How many pins does an LM555 Timer have? What is the maximum supply voltage for a 74LS08? All of this information and more is available in the manufacturer datasheet for each of these components.
In this activity you will learn how to obtain and extract information from the manufacturer datasheet for several components commonly used in digital electronics.
The same information overload is true when it comes to integrated circuits. What is the function of a MAN6760? How many pins does an LM555 Timer have? What is the maximum supply voltage for a 74LS08? All of this information and more is available in the manufacturer datasheet for each of these components.
In this activity you will learn how to obtain and extract information from the manufacturer datasheet for several components commonly used in digital electronics.
Activity 1.2.1
Combinational and sequential logic are the fundamental building blocks of digital electronics. Combinational logic, which is sometimes referred to as "combinatorial logic”, is characterized by its output being a function of the current input value.
A variety of different logic gates can be used to implement combinational logic circuits. Many of these gates will be studied in future units of this course. In this introductory unit, we will limit our designs to AND, OR, and INVERTER gates for the sake of simplicity.
In this activity you will use the Circuit Design Software (CDS) to build and test your first combinational logic circuits.
A variety of different logic gates can be used to implement combinational logic circuits. Many of these gates will be studied in future units of this course. In this introductory unit, we will limit our designs to AND, OR, and INVERTER gates for the sake of simplicity.
In this activity you will use the Circuit Design Software (CDS) to build and test your first combinational logic circuits.
Activity 1.2.2
Even though this is a course in digital electronics, it is important to understand that the world around us is analog. Virtually everything that can be designed with digital electronics is used to either control or monitor something in the world around us, and this world is analog. Thus, to be an effective designer of digital electronics, it is important for you to understand the characteristics of both analog and digital signals.
In this activity you will examine several analog and digital signals to determine their amplitude, period, and frequency. Additionally, you will gain experience using the oscilloscope within the Circuit Design Software (CDS).
In this activity you will examine several analog and digital signals to determine their amplitude, period, and frequency. Additionally, you will gain experience using the oscilloscope within the Circuit Design Software (CDS).
Activity 1.2.3
Have you ever wondered why we use the base-ten, or decimal, number system? Of course, we have ten fingers. However, the decimal number system that works so well for us is completely incompatible with digital electronics. Digital electronics only understand two states, ON and OFF. This is why digital electronics use the base-two, or binary, number system. In order for you to be able to design digital electronics, you will need to be proficient at converting numbers between the decimal and binary number systems.
In this activity you will learn how to convert numbers between the decimal and binary number systems.
In this activity you will learn how to convert numbers between the decimal and binary number systems.
Activity 1.2.4 Introduction to Sequential Logic Design
Along with combinational logic, sequential logic is a fundamental building block of digital electronics. The output values of sequential logic depend not only on the current input values (i.e., combinational logic), but also on previous output values. Thus, sequential logic requires a clock signal to control sequencing and memory and to retain previous outputs.
In this activity we will use the D flip-flop introduced in the previous lesson. We are limiting our use to this type of flip-flop in this introductory unit because of its simplicity and ease of use. The D flip-flop is just one of many different types of flip-flops that can be used to implement sequential logic circuits.
In this activity we will use the D flip-flop introduced in the previous lesson. We are limiting our use to this type of flip-flop in this introductory unit because of its simplicity and ease of use. The D flip-flop is just one of many different types of flip-flops that can be used to implement sequential logic circuits.
Activity 1.2.5 Clock Signals
Almost all development tools used today in digital electronics have an internal clock that can be integrated into your circuit design. There are times however, when you may want to generate your own simple clock signal and not depend on the internal clock of your development board or equipment like a function generator or digital writer.
The 555 Timer oscillator is one of the most common circuits used in introductory electronics. It is a favorite among beginners because of its low cost and ease of design. These are precisely the same reasons the 555 Timer is used in the Random Number Generator design.
In this activity you will simulate and create a 555 Timer oscillator. You will observe the effect that varying the value of its resistor and capacitor values has on the oscillation frequency and duty cycle.
The 555 Timer oscillator is one of the most common circuits used in introductory electronics. It is a favorite among beginners because of its low cost and ease of design. These are precisely the same reasons the 555 Timer is used in the Random Number Generator design.
In this activity you will simulate and create a 555 Timer oscillator. You will observe the effect that varying the value of its resistor and capacitor values has on the oscillation frequency and duty cycle.
Activity 1.2.6 Understanding Analog Design
The field of analog electronics is a unique discipline, distinct from the study of digital electronics. We have only scratched the surface of what you would learn if you continued your studies in this area. This project will be the last activity in our brief journey into the world of analog electronics.
In this activity you will use the Circuit Design Software (CDS) to build and test the complete analog section of the Random Number Generator design.
In this activity you will use the Circuit Design Software (CDS) to build and test the complete analog section of the Random Number Generator design.
Activity 2.1.1 AOI Design
The first step in designing a new product is clearly defining the design requirements or design specifications. These design specifications detail all of the features and limitations of the new product.
In digital electronics, the process of translating these design specifications into a functioning circuit starts with the creation of a truth table. A truth table is simply a list of all possible binary input combinations that could be applied to a circuit and the corresponding binary outputs that the circuit produces. Once the truth table is complete, a Boolean expression can easily be written directly from the truth table.
In this activity you will learn how to translate design specifications into truth tables and, in turn, write un-simplified logic expressions from these truth tables.
In future activities we will learn how to use Boolean algebra as well as a graphical technique called Karnaugh mapping to simplify these logic expressions.
In digital electronics, the process of translating these design specifications into a functioning circuit starts with the creation of a truth table. A truth table is simply a list of all possible binary input combinations that could be applied to a circuit and the corresponding binary outputs that the circuit produces. Once the truth table is complete, a Boolean expression can easily be written directly from the truth table.
In this activity you will learn how to translate design specifications into truth tables and, in turn, write un-simplified logic expressions from these truth tables.
In future activities we will learn how to use Boolean algebra as well as a graphical technique called Karnaugh mapping to simplify these logic expressions.
Activity 2.1.2 AOI Logic Analysis
What does this circuit do? Does the circuit that I designed work? If you are able to analyze AOI logic circuits, you will be able to answer these questions. The first question frequently comes up when you need to determine the functionality of a previously designed circuit. The second question will always need to be answered whenever you design a new logic circuit.
When you analyze an AOI logic circuit, you can use one of two techniques. With the first technique, you determine the circuit’s truth table from which the output logic expression is derived. With the second technique, the order is reversed. The circuit’s logic expression is determined. The truth table is then derived using this expression.
In this activity you will learn how to analyze AOI logic circuits to determine the circuit truth table and output logic expression.
When you analyze an AOI logic circuit, you can use one of two techniques. With the first technique, you determine the circuit’s truth table from which the output logic expression is derived. With the second technique, the order is reversed. The circuit’s logic expression is determined. The truth table is then derived using this expression.
In this activity you will learn how to analyze AOI logic circuits to determine the circuit truth table and output logic expression.
Activity 2.1.3 AOI Logic Implementation
Would you pay $199 for a written specification for an MP3 player? Would you pay $299 for the schematics for a cell phone? Of course not. You don’t pay for the specifications or the schematics; you pay for the product itself.
You are not quite to the point where you can design an MP3 player or a cell phone, but you can design AOI logic circuits. In this activity you will learn how to implement AOI logic circuits from logic expressions. The logic expressions will be in either Sum-Of-Products (SOP) or Product-Of-Sums (POS) form.
You are not quite to the point where you can design an MP3 player or a cell phone, but you can design AOI logic circuits. In this activity you will learn how to implement AOI logic circuits from logic expressions. The logic expressions will be in either Sum-Of-Products (SOP) or Product-Of-Sums (POS) form.
Activity 2.1.4: Boolean Algebra
Have you ever had an idea that you thought was so unique that when you told someone else about it, you simply could not believe they thought you were wasting your time with it? If so, you know how the mathematician George Boole felt in the 1800s when he designed a math system that, at the time, had no practical application. Today, however, his math system is the most important mathematical tool used in the design of digital logic circuits. Boole introduced the world to Boolean algebra when he published his work called “An Investigation of the Laws of Thought, on Which Are Founded the Mathematical Theories of Logic and Probabilities.”
In the same way that normal algebra has rules that allow you to simplify algebraic expressions, Boolean algebra has theorems and laws that allow you to simplify expressions used to create logic circuits.
By simplifying the logic expression, we can convert a logic circuit into a simpler version that performs the same function. The advantage of a simpler circuit is that it will contain fewer gates, will be easier to build, and will cost less to manufacture.
In this activity you will learn how to apply the theorems and laws of Boolean algebra to simplify logic expressions and digital logic circuits.
The moral of the story is to keep dreaming. Someday your grandchildren may be using something that you’re thinking about right now. When your grandparents were kids, do you think that they imagined someday that we would all have 10,000 songs in our pockets or a telephone in our backpacks?
In the same way that normal algebra has rules that allow you to simplify algebraic expressions, Boolean algebra has theorems and laws that allow you to simplify expressions used to create logic circuits.
By simplifying the logic expression, we can convert a logic circuit into a simpler version that performs the same function. The advantage of a simpler circuit is that it will contain fewer gates, will be easier to build, and will cost less to manufacture.
In this activity you will learn how to apply the theorems and laws of Boolean algebra to simplify logic expressions and digital logic circuits.
The moral of the story is to keep dreaming. Someday your grandchildren may be using something that you’re thinking about right now. When your grandparents were kids, do you think that they imagined someday that we would all have 10,000 songs in our pockets or a telephone in our backpacks?
Activity 2.1.5: DeMorgan's Theorem
Despite all of the work done by George Boole, there was still more work to be done. Expanding on Boole’s studies, Augustus DeMorgan (1806-1871) developed two additional theorems that now bear his name. Without DeMorgan’s Theorems, the complete simplification of logic expression would not be possible.
As we will seen in later activities, DeMorgan’s Theorems are the foundation for the NAND and NOR logic gates. In this activity you will learn how to simplify logic expressions and digital logic circuits using DeMorgan’s two theorems along with the other laws of Boolean algebra.
As we will seen in later activities, DeMorgan’s Theorems are the foundation for the NAND and NOR logic gates. In this activity you will learn how to simplify logic expressions and digital logic circuits using DeMorgan’s two theorems along with the other laws of Boolean algebra.
Activity 2.2.1: K-Mapping
At this point you have the ability to apply the theorems and laws of Boolean algebra to simplify logic expressions in order to produce simpler and more cost effective digital logic circuits. You may have also realized that simplifying a logic expression using Boolean algebra, though not terribly complicated, is not always the most straightforward process. There isn’t always a clear starting point for applying the various theorems and laws, nor is there a definitive end in the process.
Wouldn’t it be nice to have a process for simplifying logic expressions that was more straightforward, had a clearly defined beginning, middle, and end, and didn’t require you to memorize all of the Boolean theorems and laws? Well there is, and it’s called Karnaugh mapping. Karnaugh mapping, or K-Mapping, is a graphical technique for simplifying logic expressions containing up to four variables.
In this activity you will learn how to utilize the Karnaugh mapping technique to simplify two, three, and four variable logic expressions. Additionally, logic expressions containing don’t care conditions will be simplified using the K-Mapping process.
Wouldn’t it be nice to have a process for simplifying logic expressions that was more straightforward, had a clearly defined beginning, middle, and end, and didn’t require you to memorize all of the Boolean theorems and laws? Well there is, and it’s called Karnaugh mapping. Karnaugh mapping, or K-Mapping, is a graphical technique for simplifying logic expressions containing up to four variables.
In this activity you will learn how to utilize the Karnaugh mapping technique to simplify two, three, and four variable logic expressions. Additionally, logic expressions containing don’t care conditions will be simplified using the K-Mapping process.
Activity 2.2.2 Universal Gates: NAND Only
The block diagram shown below represents a voting booth monitoring system. For privacy reasons, a voting booth can only be used if the booth on either side is unoccupied. The monitoring system has four inputs and two outputs. Whenever a voting booth is occupied, the corresponding input (A, B, C, & D) is a (1). The first output, Booth, is a (1) whenever a voting booth is available. The second output, Alarm, is a (1) whenever the privacy rule is violated.
In this activity you will implement NAND only combinational logic circuits for the two outputs Booth and Alarm. These NAND only designs will be compared with the original AOI implementations in terms of efficiency and gate/IC utilization. In a future activity, these NAND only designs will be compared to the circuits implemented using only NOR gates.
In this activity you will implement NAND only combinational logic circuits for the two outputs Booth and Alarm. These NAND only designs will be compared with the original AOI implementations in terms of efficiency and gate/IC utilization. In a future activity, these NAND only designs will be compared to the circuits implemented using only NOR gates.
Activity 2.2.3 Universal Gates: NOR Only
In this activity you will revisit the voting booth monitoring system introduced in Activity 2.2.2 NAND Logic Design. Specifically, you will be implementing the NOR only combinational logic circuits for the two outputs Booth and Alarm. In terms of efficiency and gate/IC utilization, these NOR only designs will be compared with the previously designed AOI and NAND implementations.
Activity 2.2.4 Design Tool: Logic Converter
![Picture](/uploads/2/2/4/2/22423118/6602219_orig.png)
Now that you are all experts at logic simplification using Boolean algebra and K-Mapping and can implement virtually any combinational design using AOI, NAND, and NOR gates, it’s time to let you in on a little secret. A tool located within the Multisim Circuit Design Software, called the Logic Converter, can do much of this work for you. You might be asking yourself why you weren’t given this tool sooner. As an engineer you need to know how to design these types of circuits with and without the aid of such tools. Besides, who do you think designs tools like the Logic Converter? That’s right, an engineer.
In this activity you will complete a brief tutorial and use the Logic Converter to create and simulate both an AOI and NAND circuit design.
In this activity you will complete a brief tutorial and use the Logic Converter to create and simulate both an AOI and NAND circuit design.
Activity 2.3.1
We all know that digital electronics use the binary number system. However, with new computers containing 32, 64, and even 128 bit data busses, displaying numbers in binary is quite cumbersome. For example, a single piece of data on a 64-bit data bus would look like this:
0110100101110001001101001100101001101001011100010011010011001010
Obviously, presenting data in this form would invite error. For this reason we use the hexadecimal (base 16) and, to a lesser extent, the octal (base 8) number systems. In this activity you will learn how to convert numbers between the decimal, binary, octal, and hexadecimal number systems.
0110100101110001001101001100101001101001011100010011010011001010
Obviously, presenting data in this form would invite error. For this reason we use the hexadecimal (base 16) and, to a lesser extent, the octal (base 8) number systems. In this activity you will learn how to convert numbers between the decimal, binary, octal, and hexadecimal number systems.
Activity 2.3.2
What do alarm clocks, cable TV converter boxes, home answering machines, and inexpensive calculators all have in common? In addition to being built from electronics, many also include seven-segment displays as part of their design.
There are two types of seven-segment displays: common cathode and common anode. Understanding how these displays work and the differences between them is fundamental to designing many different types of electronic devices. In this activity you will learn how to use seven-segment displays to display both alpha and numeric characters. You will also be introduced to the Seven-Segment Display Driver.
There are two types of seven-segment displays: common cathode and common anode. Understanding how these displays work and the differences between them is fundamental to designing many different types of electronic devices. In this activity you will learn how to use seven-segment displays to display both alpha and numeric characters. You will also be introduced to the Seven-Segment Display Driver.
Activity 2.3.3
Though it may be hard for you to believe, there was once a day when not everyone had a cell phone. Every house had one phone. That’s right, just one. How was this phone connected to all of the other phones in your town or country? Obviously it isn’t practical to have a wire from your phone connected directly to all other phones individually. This would require an unimaginable amount of wire traveling to and from every home in America. The solution to this problem is for a group of homes to share one wire with another group of homes. This is sharing of a resource and, in this case, the wire is a classic application of a multiplexer/de-multiplexer circuit.
Another classic application of multiplexing/demultiplexing is the way that seven-segment display signs are wired. In this activity you will implement two simple display signs. The first will not take advantage of multiplexing and the second will.
Another classic application of multiplexing/demultiplexing is the way that seven-segment display signs are wired. In this activity you will implement two simple display signs. The first will not take advantage of multiplexing and the second will.
2.3.5
Do negative numbers exist? Did you know that great mathematicians throughout history argued about the very existence of negative numbers? William Frend, a 16th century European mathematician, refused to accept the existence of negative numbers.
In his book The Principles of Algebra (1796), he wrote:
"to attempt to take [a number] away from a number less than itself is ridiculous."
Even Augustus DeMorgan, author of the famed DeMorgan Theorems, thought that numbers less than zero were unimaginable.
We all know now that negative numbers do exist. We learned about them in the third grade, and we use them every day. A golfer who scores a 67 on a par 72 course would describe her score as 5 under par, or -5. Likewise, in the northern climate of the United States, the winter temperatures can drop to 10° below zero, or -10° Fahrenheit.
If negative decimal numbers exist and you can convert a decimal number into its binary equivalent, then there must be a way to represent negative binary numbers. In this activity you will learn how to express numbers in their 8-bit - 2’s complement binary equivalent. You will use these equivalencies to perform simple addition and subtraction.
In his book The Principles of Algebra (1796), he wrote:
"to attempt to take [a number] away from a number less than itself is ridiculous."
Even Augustus DeMorgan, author of the famed DeMorgan Theorems, thought that numbers less than zero were unimaginable.
We all know now that negative numbers do exist. We learned about them in the third grade, and we use them every day. A golfer who scores a 67 on a par 72 course would describe her score as 5 under par, or -5. Likewise, in the northern climate of the United States, the winter temperatures can drop to 10° below zero, or -10° Fahrenheit.
If negative decimal numbers exist and you can convert a decimal number into its binary equivalent, then there must be a way to represent negative binary numbers. In this activity you will learn how to express numbers in their 8-bit - 2’s complement binary equivalent. You will use these equivalencies to perform simple addition and subtraction.
3.1.1
Flip-flops are the fundamental building blocks of sequential logic. There are a variety of different flip-flop types and configurations. In this activity (and this course) we will only be studying two types of flip-flop. The D flip-flop which was introduced in Unit 1 and the J/K flip-flop. After reviewing the basic operation of the 74LS74 D and the 74LS76 J/K flip-flops, this activity will examine two applications of flip-flops.
Note: Where did these flip-flops get their name? The D in the D flip-flop stands for data. No one is absolutely sure where the J/K name originated, but one theory is that it is named after Jack Kilby, the inventor of the integrated circuit.
Note: Where did these flip-flops get their name? The D in the D flip-flop stands for data. No one is absolutely sure where the J/K name originated, but one theory is that it is named after Jack Kilby, the inventor of the integrated circuit.
3.1.2
In this activity you will simulate an event detector circuit using a D flip-flop. This design will sound an alarm if a beam of light is disrupted on its photosensitive detector input.
The circuit shown below is a photosensitive event detector. This circuit sounds an alarm if the beam of light between the 12-volt incandescent bulb and phototransistor is disrupted.
This circuit would be used as part of a larger burglar alarm system. As the name implies, a phototransistor is a transistor that is sensitive to light. In the event detection circuit, the phototransistor acts as a switch. As long as the phototransistor is in the proximity of the incandescent bulb, the transistor will be on. This, in turn, will hold the CLK input of the flip-flop at a logic zero. If the beam of light is disrupted, the phototransistor will be turned off. When the transistor is off, the CLK input of the flip-flop will be pulled high through the 5.6 kW resistor. This zero-to-one transition will toggle the Q output to a one, which will turn the buzzer on. The buzzer will remain on until the reset button is pressed.
The circuit shown below is a photosensitive event detector. This circuit sounds an alarm if the beam of light between the 12-volt incandescent bulb and phototransistor is disrupted.
This circuit would be used as part of a larger burglar alarm system. As the name implies, a phototransistor is a transistor that is sensitive to light. In the event detection circuit, the phototransistor acts as a switch. As long as the phototransistor is in the proximity of the incandescent bulb, the transistor will be on. This, in turn, will hold the CLK input of the flip-flop at a logic zero. If the beam of light is disrupted, the phototransistor will be turned off. When the transistor is off, the CLK input of the flip-flop will be pulled high through the 5.6 kW resistor. This zero-to-one transition will toggle the Q output to a one, which will turn the buzzer on. The buzzer will remain on until the reset button is pressed.
3.2.1
Asynchronous counters can be designed to count up or count down using Small-Scale Integration (SSI). The small-scale design can utilize almost any flip-flop type. To observe this process, we will simulate and analyze multiple 3-bit counters based on both D and J/K flip-flops. For both the D flip-flop and J/K flip-flop, we will modify circuits so that they will count up or count down. Remember, for up counters, connect the CLK to the Q output of the opposite polarity. For down counters, connect the CLK to the Q output of the same polarity.
Activity 3.2.2
In the last activity we saw how easy it was to design asynchronous counters using either the D or J/K flip-flop. However, these designs had two big limitations.
First, the count limit had to be a power of two (e.g., 2, 4, 8, 16, 32, etc.).
All counts also started or ended at a count of zero. In the real world, we frequently need to set the count limit to some arbitrary value (10, 25, 85, etc.). More often than not, the starting or ending value will not be zero. For this reason we must design asynchronous modulus counters.
An asynchronous modulus counter, or mod-counter, uses the addition of simple combinational logic to a standard asynchronous counter to set the count limit and starting point. In this activity we will simulate and build a mod-5 counter that has a starting count of one.
This activity will also introduce using a clock signal with a PLD.
First, the count limit had to be a power of two (e.g., 2, 4, 8, 16, 32, etc.).
All counts also started or ended at a count of zero. In the real world, we frequently need to set the count limit to some arbitrary value (10, 25, 85, etc.). More often than not, the starting or ending value will not be zero. For this reason we must design asynchronous modulus counters.
An asynchronous modulus counter, or mod-counter, uses the addition of simple combinational logic to a standard asynchronous counter to set the count limit and starting point. In this activity we will simulate and build a mod-5 counter that has a starting count of one.
This activity will also introduce using a clock signal with a PLD.
Activity 3.2.3
Manufactures of integrated circuits frequently take digital circuit designs, which are commonly implemented with SSI gates, and create equivalent Medium Scale Integrated (MSI) circuits. The 74LS93 4-Bit Counter is an example of a Medium Scale Integrated (MSI) circuit.
In this activity, we will simulate and analyze a 4-Bit asynchronous counter using a 74LS93 4-Bit Counter. We will also explore how to suspend a count and reset a count.
In this activity, we will simulate and analyze a 4-Bit asynchronous counter using a 74LS93 4-Bit Counter. We will also explore how to suspend a count and reset a count.
Activity 3.2.4
In this design project, you will have the opportunity to draw together all of the concepts and skills that you have developed pertaining to the topic of asynchronous counter design. You will design, simulate, and build a Now Serving Display. This is the type of display that you would commonly see at a deli counter.
Activity 4.1.1
Up until this point in the course, almost all of your designs have utilized push buttons or switches as inputs and LEDs or seven-segment displays as outputs. In this design project, you will have the opportunity to incorporate motors and input sensors other than the ones you are familiar with on the Digital Logic Board (DLB). You will design, simulate, and create a Copier Jam Detector.
Problem 4.1.3
Now that you have seen examples of state machines and how they work, it is time for you to create your own. The state machine you will be designing is based on the tollbooth gate example. If you are a former Gateway to Technology student you might remember creating a similar design using the VEX® Cortex Controller and programming it with RobotC.
In this design you are required to use a PLD to create a functioning prototype. Can you think of any advantages to creating this design in simulation and exporting it to a PLD rather than using the VEX Cortex Controller?
The tollbooth gate state machine has four inputs and four outputs.
Inputs
OS - Open Switch Pushbutton
This input is activated by the user. When the button is pressed, it outputs a logic one and causes the gate to open.
This input button is a pushbutton switch located on the DLB.
CS - Close Switch Pushbutton
This input is activated by the user. When this button is pressed, it outputs a logic one and causes the gate to close.
This input button is also a pushbutton switch located on the DLB.
OL - Open Limit Switch
This input is activated by the gate mechanism when it is fully open. When this input switch is pressed, it outputs a logic one.
This limit switch is located on the test fixture.
CL - Close Limit Switch
This input is activated by the gate mechanism when it is fully closed. When this input switch is pressed, it outputs a logic one.
This limit switch is located on the test fixture.
Outputs
MO - Motor Open
This output is a logic one.
It will cause the tollbooth gate to open.
MC - Motor Close
This output is a logic one.
It will cause the tollbooth gate to close.
GO - Gate Open
This output is connected to an LED on the DLB.
It is ON when the gate is fully open.
GC - Gate Closed
This output is connected to an LED on the DLB.
It is ON when the gate is fully closed.
In this design you are required to use a PLD to create a functioning prototype. Can you think of any advantages to creating this design in simulation and exporting it to a PLD rather than using the VEX Cortex Controller?
The tollbooth gate state machine has four inputs and four outputs.
Inputs
OS - Open Switch Pushbutton
This input is activated by the user. When the button is pressed, it outputs a logic one and causes the gate to open.
This input button is a pushbutton switch located on the DLB.
CS - Close Switch Pushbutton
This input is activated by the user. When this button is pressed, it outputs a logic one and causes the gate to close.
This input button is also a pushbutton switch located on the DLB.
OL - Open Limit Switch
This input is activated by the gate mechanism when it is fully open. When this input switch is pressed, it outputs a logic one.
This limit switch is located on the test fixture.
CL - Close Limit Switch
This input is activated by the gate mechanism when it is fully closed. When this input switch is pressed, it outputs a logic one.
This limit switch is located on the test fixture.
Outputs
MO - Motor Open
This output is a logic one.
It will cause the tollbooth gate to open.
MC - Motor Close
This output is a logic one.
It will cause the tollbooth gate to close.
GO - Gate Open
This output is connected to an LED on the DLB.
It is ON when the gate is fully open.
GC - Gate Closed
This output is connected to an LED on the DLB.
It is ON when the gate is fully closed.
Activity 4.1.2
The block diagram shown below is for a simple state machine that counts out the last four digits of a phone number. This design has two inputs and seven outputs.
In addition to the clock input required for all state machines, this design’s second input is called Enable (EN). Whenever the EN input is a logic (1), the outputs will continuously cycle through the four digits of the phone number. Whenever the EN input is a logic (0), the outputs will hold at their current values.
The three (or four) outputs from the state machine are the binary encoding of the phone number digits. You will only need the fourth output if the phone number contains an 8 (1000) or a 9 (1001). The binary output of the state machine connects to a decoder and a seven-segment display, which will display the decimal equivalent of each binary number.In this activity you will design, simulate, and program (to the FPGA chip on the Cmod-S6) a state machine that counts out the last four digits of your phone number.
In addition to the clock input required for all state machines, this design’s second input is called Enable (EN). Whenever the EN input is a logic (1), the outputs will continuously cycle through the four digits of the phone number. Whenever the EN input is a logic (0), the outputs will hold at their current values.
The three (or four) outputs from the state machine are the binary encoding of the phone number digits. You will only need the fourth output if the phone number contains an 8 (1000) or a 9 (1001). The binary output of the state machine connects to a decoder and a seven-segment display, which will display the decimal equivalent of each binary number.In this activity you will design, simulate, and program (to the FPGA chip on the Cmod-S6) a state machine that counts out the last four digits of your phone number.