DE Unit 2: Digital Logic

Understanding and implementing the Circuit Design Process

CIRCUIT DESIGN OVERVIEW

Our study of circuits will build to more complicated ideas in this unit.  Last unit we followed some tutorials to build and investigate some fairly simple circuits and measure some of their properties.  In this unit we get to look at the different logical ways circuits can be put together, as well as introduce some of the basic logic gates that get used. While this is still an introductory unit, we’ll still cover some essential topics in electronics that start with the Circuit Design Process:

  • Define a problem situation – usually through a written description
  • Create a truth-table or some other mathematical representation of the logic
  • Write a logic expression
  • Simplify the logic expression – there are a variety of ways to do this
  • Create a circuit using And/Or/Inverter (AOI) Logic

Certainly, this process is more complicated than the simpler circuits we’ve looked at so far might suggest.  As our units continue, we’ll get more detailed information about each of these steps until we can do the whole thing ourselves!  In this second unit, we’ll introduce three major ideas:

  1. STEP 1: Investigate combinational logic as it is used in the development of digital circuits
  2. STEP 2: Explore sequential logic in circuits, and understand how a “555 Timer” works
  3. STEP 3: Apply this knowledge in the Random Number Generator and understand how it works

When you’re done, you will have seen the full mix of things that the rest of our class will talk about.  You will have built some pre-designed circuits, considered the role of IC chips, and analyzed working systems.  

PART 1: COMBINATIONAL LOGIC

(20 pts) About 3 days

This part of the unit revolves around the idea of a car’s seat belt alert buzzer.  Here you’ll implement a circuit that simulates that system and investigate how it works in detail.  You’ll also get to apply some of your math knowledge as we look at analog and digital signals.

PART 2: SEQUENTIAL LOGIC

(30 pts) About 3 days

Sequential logic is used often to create counters of various kinds. In this part of the unit you’ll create and investigate a sequential counter that counts in binary. Then, you’ll use an oscilloscope to explore how it counts.  We’ll also look at our first IC chip: the 555 Timer.

PART 3: UNDERSTANDING DESIGN

(20 pts) About 3 days

In this last part of the unit, we’ll look back to random number generators like the one used in our Digital Dice.  Random number generators can be made using either analog or digital systems, and here we’ll get to simulate both and think more about how they work.

Part 1: Combinatorial Logic

Building circuits using logic gates and exploring wave signals

Circuit Basics Overview

Digital circuits can do a wide variety of things for us, and they rely heavily on digital signals to do so.  Whenever we have a mechanical device with logical on/off inputs, a digital circuit can be used to model and control that system. In this first unit, we’ll look at how a digital circuit can be used to simulate the buzzer in a car that is triggered by a combination of driver seatbelt, ignition key, and driver door states.  Each of these can be further described using digital signals that are a combination of simple on-off cycles.

GRADING & PROCESS

 Watch the video on Circuit Design and take some careful notes.  Be sure to compare this process to the Engineering Design Process we’ve used in other engineering classes.

 Watch the presentation on the Seat Belt Circuit and add to your notes.

 Build the seat belt circuit in Multisim and explore the different states of the inputs by completing the activity.

 Watch the presentation on Analog and Digital Signals.  Make sure to take careful notes on the different calculations we can make from the graph of the waves!

 Complete the Analog & Digital Signals Assignment

 Have Mr. Benshoof approve your notes and completed Assignments

Circuit Design

Seat Belt Circuit Overview

Analog & Digital Signals

What’s Due In Digital Logic Part 1: Wiring

  • Circuit Design Notes
  • Seat Belt Circuit Notes
  • Seat Belt Circuit Simulation
  • Signals Notes
  • Analog & Digital Signals Assignment
  • Mr. Benshoof’s Approval

 

Part 2: Sequential Logic

Designing digital counters with sequential logic and the 555 Timer
IC Chip Reference

When creating digital circuits, electrical engineers often have a choice between combinational logic (like the Seat Belt Circuit), and sequential logic.  Sequential Logic works in sequence, where the output of one part of the circuit is actually triggering the functions of the later parts of the circuit. In this unit we’ll look at a relatively simple sequential circuit and see how it can be used to create a binary counter.  We’ll also look at our first Integrated Circuit (IC) chip, the 555 Timer!

GRADING & PROCESS

 Watch the video on Sequential Counters and take a page of careful notes including a nice labeled diagram of the D-Flip-Flop.

 Use Multisim to build the binary counters and complete the Counters Activity

 Watch the presentations on Clock Signals and on the 555 Timer.  Be sure and take a page of careful notes, including a labeled diagram of the 555 Timer.

 Build the 555 Timer in Multisim and investigate the different Periods, Frequencies, and Duty Cycles for different resistor/capacitor combinations.  Record your results in your engineering notebook.

 Have Mr. Benshoof check-off each simulation and activity answers.

Sequential Circuits Overview

Clock Signals

555 Timer

What’s Due In Part 2: Sequential Logic

  • Sequential Logic Notes
  • Counters Activity
  • Clock Signal Notes
  • 555 Timer Investigation
  • Benshoof’s Check-off

Here’s what’s due in Part 1: Wiring

  1.  Take a full page of notes on Sequential Counters and the D-Flip Flop
  2. Complete the Counters Activity by working in Multisim
  3. Take a full page of notes on Clock Signals and the 555 Timer
  4.  Build the 555 Timer in Multisim and investigate various parameters
  5. Have Mr. Benshoof check-off your simulations, notes, and results

Part 3: Understanding Design

Revisiting the Random Number Generator with Analog & Digital design

Random Number Generators

The last part of this unit has you build two more simulated circuits in Multisim.  The first of these circuits demonstrates how an analog circuit – using an analog signal/wave – is used in to help generate random numbers. The second circuit finished the job, turning the random number into the LED display. Since our class is about digital electronics, the ideas from this circuit will resurface and be explained further throughout the year.  In this part of the unit, our job is to try and understand how the 555 Timer works and how complex circuits can combine ideas for complicated outputs!

GRADING & PROCESS

 Take a full page of notes on Analog Design, including a sketch of the analog block of the Random Number Generator that will be built in this section.

 Build the modified analog random number generator in Multisim and answer the corresponding questions.

 Take a full page of notes on Digital Design, including a sketch of the two digital components: the Sequential Logic Section and the Combinational Logic Section that will be built.

 Build the digital random number generator parts in Multisim and answer the corresponding questions.

 Have Mr. Benshoof check-off your notes, simulations, and question answers.

Understanding Design Overview
Understanding Analog Design
Understanding Digital Design

What’s Due In Part 3: Understanding Design

  • Analog RNG Notes
  • Analog RNG in Multisim
  • Digital RNG Notes
  • Digital RNG in Multisim
  • Mr. Benshoof’s Check-Off

Here’s what’s due in Part 3: Build a Project!

  1. A full page of notes on Analog Design including picture of Analog Random Number Generator
  2. Build Analog Random Number Generator in Multisim and answer questions
  3.  A full page of notes on Digital Design including picture of Digital Random Number Generator
  4.  Build Digital Random Number Generator in Multisim and answer questions
  5. Have Mr. Benshoof check-off your notes, simulations, and question answers.

Double Check: Unit Expectations

Check what you need to have completed by the unit deadline
The purpose of this unit is to illustrate how large circuits come together to do complicated things. The analog random number generator takes advantage of capacitors to create random results; here we investigate this circuit, but we’ll spend the rest of our class on digital designs.  The digital random number generator uses clock signals and timers to create random numbers, and this circuit does a good job of demonstrating both sequential logic and combinational logic: two topics that our class will focus on at great length.  In the end, you will have had exposure to all the topics coming up in our class.

Engineering Notebook:

(Part 1) You should have taken a full page of notes on the Circuit Design Process and the Seat Belt Circuit

(Part 1) You should have taken a full page of notes on Analog & Digital Signals

(Part 2) You should have taken a full page of notes on both Sequential COunters & D Flip-Flops as well as on Clock Signals & 555 Timers

(Part 3) You should have taken a full page of notes on both Analog Design and Digital Design.

Building & Making:

(Part 1) You should have built the Seat Belt Circuit and completed the activity.

 (Part 1) You should have completed the Analog & Digital Signals Assignment

(Part 2) You should have completed the Counters Activity including the work in Multisim

(Part 2) You should have built the 555 Timer in Multisim and used it to investigate its mathematical properties.

 (Part 3) You should have built your Analog Random Number Generator and answered the corresponding questions about it.

 (Part 3) You should have built your DIgital Random Number Generator and answered the corresponding questions about it.

Checkpoints & Quizzes:

(Part 1) Benshoof should have checked-off your notes and completed assignments.

(Part 2) Benshoof should have checked-off your notes, simulations, and results from the simulation.

(Part 3) Benshoof should have confirmed your notes, RNG simulations, and question answers.