Lecture 13: Basic Circuit Theory I

EEN 112: Introduction to Electrical and Computer Engineering

Professor Eric Rozier, 4/1/13

QUIZ GRADES AND RESULTS

Quiz III Grade Distribution

Grade Distribution

REVIEW

Identify the Architecture

CPU

ProgramMemory

DataMemory

Bus

Identify the Architecture

CPU

ProgramMemoryBus

Bus DataMemory

Memory

• Nonvolatile memory? • Volatile memory?

Memory

• Nonvolatile memory?– Retains stored

information even when unpowered

– Long-term or persistent storage

• Volatile memory?– Requires constant power

for storage– Information is lost when

the power supply is off or interrupted

– Temporary memory

What is a Microprocessor?

What is a Microprocessor?

• Single chip that contains the whole CPU– Fetches, decodes, and executes instructions stored

in memory– Can access memory, I/O, and peripherals

What is a Microcontroller?

What is a Microcontroller?

• Microprocessor + on-chip memories and I/O devices

• “Computer-on-a-chip”– Contains the CPU– Memory– Some I/O and peripherals

What is an Embedded System?

What is an Embedded System?

• Special purpose computer system, usually completely inside a device it is designed to control

• Works to help solve specific problems, and perform pre-defined tasks

• Usually contains inputs (sensors), a microcontroller, and outputs (actuators and indicators)

MIDTERM II

Midterm II

• Midterm II, this Wednesday!• Covered topics

– Signal Processing (Quiz II, and lectures online)– Microprocessors/Microcontrollers (Quiz III, and

lectures online)– PBASIC Programming (last lecture, online)

BASIC CIRCUIT THEORY

Atoms

Atoms

• Smallest part of an element.

• Nucleus surrounded by “orbiting” electrons– Protons – positive charge– Neutrons – no charge– Electrons – negative

charge

Electron Configurations

• Electrons move independently in an orbital, an average field wave function

Electron Configurations

• Arranged in electron shells– Shells contain fixed numbers of electrons

• 1st shell – 2 electrons• 2nd shell – 8 electrons• 3rd shell – 18 electrons• 4th shell – 32 electrons• etc

Electron Configurations

• 14 protons, 14 neutrons, 14 electrons

• 1st shell – 2/2 electrons• 2nd shell – 8/8 electrons• 3rd shell – 2/18

electrons

Electron Configurations

• Electrons in the outermost shell are known as valence electrons

• When valence electrons gain sufficient energy, they can break away and become free electrons.– Free electrons can drift from one atom to another– Free electrons make electrical current possible

Free Electrons

• The number of free electrons in a material allow it to be classified– Conductors

• allow current to flow easily• large numbers of free electrons• Examples: silver, copper, gold

Free Electrons

• The number of free electrons in a material allow it to be classified– Conductors– Semiconductors

• less free electrons• unique characteristics, basis for modern electronics• Examples: silicon, germanium

Free Electrons

• The number of free electrons in a material allow it to be classified– Conductors– Semiconductors– Insulators

• very small number of free electrons• poor conductors• Examples: ceramics, rubber, air, dry paper

Electric Charge (Q)

• Two types of charges, positive and negative• Q – the electrical charge

– Units in Coulombs (C)• One electron has a charge of 1.6*10^(-19) C• In 1 Coluomb there are 6.25*10^18 electrons

Current

• Rate of flow of electrons through a circuit• Symbol is I, measured in Amperes (or Amps)• The flow of on coulomb/second is one Amp

Voltage

• Related to potential energy

• Measured between two points– One of those points is “ground”, a reference level

to which all voltages are compared– If a pin is at 5V, it is measured at 5V with respect

to ground

Resistance

• Voltage and current related by resistance

• When voltage is applied to an electrical system, current begins to flow– Level of current is

determined by resistance of the system

Types of Resistors

Resistors• Resistance value in an electrical circuit is given

in Ohms, and represented by R

Resistors

Ohm’s Law

• Ohm’s Law – The amountof current (I) that will flow isproportional to the voltage(V) applied, and inverselyproportional to theresistance (R) of the circuit

• I = V/RAs resistance increases, current decreases

Hydraulic Analogy

• Consider the diagram, when the valve is released, what will happen?

Hydraulic Analogy

• Flow rate (I) dependent on:• (V) pressure of the

tanks• Restriction (R) of

flow from the valve

Batteries

• Batteries feature surplus electrons on one side, and a deficiency of electrons on the other side (holes)

Flow of electrons

Power (P)

• Power measures the rate of energy conversion• For a simple direct current (DC) system, it

measures the rate at which electrical energy is converted into heat by power-dissipating resistive elements

Power (P)

• Lightbulbs convert electrical energy into heat and light– Unit for electrical power is familiar in this context– The Watt– P = V I

• Using Ohm’s law and the power equation…– P = V I = V^2/R = I^2 R

WRAP UP

Wrap Up

• Exam next class• Quiz III corrections due next

Monday