introduction to digital electronics welcome to mit! instructor: alex hanson
TRANSCRIPT
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Introduction to Digital ElectronicsWelcome to MIT!
Instructor: Alex Hanson
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About the Instructor
Alex HansonFrom: Salt Lake City, UTCollege: Dartmouth College – Electrical Engineering, Engineering Sciences, and PhysicsNow: Graduate student in Electrical Engineering and Computer Science at [email protected]
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About the Class
Professions
Engineering
Mechanical
Chemical
Civil
Electrical
Analog Circuits
Digital Circuits
Power Electronics
Signal Processing
…
…
Medicine
Law
Business
…
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About the Class
• Before this class: Prerequisites– Algebra I is required – if you feel that you do not
meet this requirement, don’t worry. Talk to me after class.
• After this class: Majors and Careers– All electrical engineers know digital electronics– Digital integrated circuits, embedded systems– Medical devices are almost all electronic– Med schools, law schools, and finance industry love
engineering majors
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Syllabus
• Required participation– Attendance, good-faith effort, good behavior
• Homework– Will give for practice, will evaluate if desired– Optional Textbook: • Digital Design by Frank Vahid
• Lab-based class…– 30-60 min “class time” – 60+ min “lab time”
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Labs – Respect and Safety
• Don’t break things• Don’t stab yourself• Don’t shock yourself• Don’t “short” batteries
• Clean up
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Course Objectives
• By the end of this course, you will be able to:– Build a breadboard prototype from a schematic– Install integrated circuits from info on datasheets– Design combinational logic blocks (decision
making)– Design sequential logic blocks (sequential
thinking)– Implement an idea into a custom digital circuit
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Today
• Introduction to Analog/Digital Information• Introduction to Electricity • Introduction to Lab Practice• Lab – Analog to Digital Converter
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Today
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Electricity – Information and Energy
• We encode information in the form of electrical signals and use those signals to communicate
• We transfer energy in the form of electricity to do useful work
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Analog and Digital Codes
• Information that uses an analog code is one which can represent any value
• “An analog signal is continuous”– Example – we want to communicate information about a
force, so we make an electrical “code” where the voltage is a constant times the force
– Just like the “real-world” value , the coded value can take on any value
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Analog and Digital Codes
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Analog and Digital Codes
• Information that uses a digital code is one which can only represent values in steps
• “A digital signal is discrete”– Example – we want to have information about a force, so
we make a code where “1” means 1 Newton, “2” means 2 Newtons, etc.
– If the real force is 5.8 Newtons, that information is encoded as “6” (depending on the conversion)
– Unlike the “real-world” value , the coded value can only take discrete values.
– We “throw away” information when digitizing, always an approximation
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Analog and Digital Codes
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What is voltage anyway?
• The amount of potential energy per charge in a configuration is the configuration’s voltage
• Since voltage and energy are so closely related, people often refer to places in a circuit with high voltage as being “energized”
• “Electric Potential” = “Voltage”
• Like charges (++ or --) repel each other, so it takes energy to push them together
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What is voltage anyway?• In a conductor (metal) electrons can move about
freely, and will spread out on the surface.• It turns out that this configuration causes the
voltage to be the same everywhere on the metal.• We can sensibly talk about “the voltage on a wire”
without specifying where on the wire.
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Voltage
• How many voltages are in this circuit?
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Voltage
• There are 4 voltages
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Voltage, Force, and Current
• An electron experiences a force which will try to move the electron toward higher voltage. In metals, there very little “friction.”
• Some things “get in the way” and slow down the flow of electrons, like resistors
• The flow of electrons is called “current”
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A note on signs
• Electrons (negative charges) flow in a circuit, and they flow “backward” from low voltage to high voltage
• To avoid confusion with the double negative, we usually think about positive charges moving from high voltage to low voltage (“conventional current”).
• We know this isn’t true, but it’s a convention that helps us keep everyone on the same page.
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Current• What direction will electrons flow?• What direction does “conventional current” flow?
𝟓𝑽 3
20
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Current• What direction will electrons flow?• What direction does “conventional current” flow?
𝟓𝑽 3
20
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Current• Conventional current follows purple arrows• Electrons move the opposite direction
𝟓𝑽 3
20
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Voltage and Current
• Electric potential (voltage) is a property of a location. We talk about voltage at a node.
• The voltage difference between two points is the voltage across a component.
• Electric current is a property that goes through a path. We talk about current through a component.
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Today’s ProjectA “Flash” Analog to Digital Converter
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Today’s ProjectA “Flash” Analog to Digital Converter
Components
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Analog to Digital Conversion
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Unary or “Thermometer” Code
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Component 1 – Resistor String
Current is same through all resistors => so is the voltage drop across each resistor.
4.8 V
3.6 V
2.4 V
1.2 V
6.0 V
0.0 V
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Component 2 - Comparator
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Component 3 – Light Emitting Diode• Diodes allow current in only one direction• Diodes will only turn on with at least 0.5 V
across them
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Current Limiting in LEDs
• What would the current be without the resistor?
• What would happen if we made this circuit in real life?
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Current Limiting in LEDs
• ALWAYS use a resistor in series with an LED• Always use a resistor that’s BIG ENOUGH to
limit the current– How big is big enough? Depends on the current
limit of the LED. Usually 330 Ohm is sufficient.
OTHERWISE YOU WILL DESTROY YOUR LED, OR WORSE, YOUR BATTERY
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Component 4:Force Sensing Resistor (FSR)
“Piezoresistance”
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Component 5 – Op Amp• An Op-Amp amplifies the difference between two inputs,
usually operated in feedback (an advanced topic). We will use an op-amp in our force-measurement circuit.
“Unity Gain Buffer” Configuration
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Today’s ProjectA “Flash” Analog to Digital Converter
Sub-Systems
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Sub-System 1: Transduction• “Transduction” is the conversion of real-world
information (force, altitude, speed, etc.) into an electrical signal, usually analog
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Sub-System 2: “Flash” ADC
Digital code representing the analog input
Real-world information encoded as an analog signal
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Sub-System 3: Display• We would like an easy way to see the output
of our converter. For this project, we will use an LED bar.
• The output of each comparator will turn on/off an LED
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System 3 Modification• Our comparators can’t push current; they can
pull or turn off (“open circuit”)
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System 3 Modification• Our comparators can’t push current; they can
pull or turn off (“open circuit”)
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System 3: Option 1
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System 3: Option 2
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Final Diagram
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Today’s ProjectA “Flash” Analog to Digital Converter
Assembly
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BreadBoards
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Integrated Circuits
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Integrated Circuits
• Always remember to connect all power pins and ground pins, in addition to inputs/outputs
• Align integrated circuits in the same way (usually notch to the left)
• Pins can be sharp – be careful!• You may have to bend the pins in slightly to
get them to fit in the breadboard – be gentle
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Resistors
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LEDs
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Have at it!
• Teams of 3-6 (limited supplies)• EVERYTHING is to be kept. THROW NOTHING
AWAY.• Keep your breadboard neat, try to color code
your signals, USE RED FOR +6V and BLACK FOR GROUND.
• See my example project as a reference.• The room must be SPOTLESS before we leave.
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Image References• http://www.1epoxyflooring.com/wp-content/gallery/flooring-salt-lake-city/saltlakecityflooring.jpg• http://m-static.flikie.com/ImageData/WallPapers/1a351f9b3c0244bdafbf54c4cc3cb2f6.jpg• http://drleonardcoldwell.com/wp-content/uploads/2014/03/cell-phones.jpg• http://hacks.mit.edu/by_year/1991/fire_hydrant/full_large.gif• https://upload.wikimedia.org/wikipedia/commons/d/d4/Electric_car_charging_Amsterdam.jpg• http://screaminfx.com/images/tech-images/what-is-analog-verse-digital-explanation.jpg• https://learn.sparkfun.com/tutorials/what-is-electricity• http://www.physicsclassroom.com/Class/estatics/u8l1d1.gif• http://wikieducator.org/images/c/c3/Simple_circuit.gif• "CPT-Sound-ADC-DAC" by A-D-A_Flow.svg: Teeks99derivative work: Pluke (talk) - This file was derived from: A-D-A Flow.svg:. Licensed under CC BY-SA 3.0 via Wikimedia
Commons - https://commons.wikimedia.org/wiki/File:CPT-Sound-ADC-DAC.svg#/media/File:CPT-Sound-ADC-DAC.svg• http://cdn.instructables.com/F15/4TZ5/HQKY9IMI/F154TZ5HQKY9IMI.LARGE.jpg• http://www.piclist.com/images/www/hobby_elec/gif/dance2321.gif• http://www.electro-labs.com/wp-content/uploads/LED-circuit-symbol.jpg• https://cdn.sparkfun.com/assets/4/6/2/1/4/515f3293ce395f4a25000000.png• https://ccrma.stanford.edu/wiki/Images/e/e4/FSR_diagram.gif• http://learn.parallax.com/sites/default/files/content/shield/Bargraph-Arduino-Demo/Bargraph4.png• http://www.adafruit.com/images/1200x900/1815-04.jpg• http://www.ibiblio.org/kuphaldt/electricCircuits/Semi/03033.png• http://i.stack.imgur.com/C0ztU.png• http://obrazki.elektroda.pl/4858974200_1353737433.png• http://www.electronicshub.org/wp-content/uploads/2013/06/Breadboard-Connections.png• http://www.crazybutable.com/stella/images/full/full_stella-8663.jpg• http://cdn.instructables.com/FU0/11AZ/GYGF8IV4/FU011AZGYGF8IV4.LARGE.jpg• http://www.sci-spot.com/images/Accel/resistorboard.jpg• http://wyxs.net/web/wiimote/digital_whiteboard/symbol_led.jpg