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 Program Memory Data Memory Program Memory Data Memory Bus

Identify the Architecture CPU Program Memory Bus Data Memory Data 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?

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?

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?

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

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

Electron Configurations 14 protons, 14 neutrons, 14 electrons 1 st shell – 2/2 electrons 2 nd shell – 8/8 electrons 3 rd 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 amount of current (I) that will flow is proportional to the voltage (V) applied, and inversely proportional to the resistance (R) of the circuit I = V/R As 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