Today's Outline

• digital hardware basics:
  • resistors and LEDs
  • Ohm's law
  • transistors and switches
  • voltages as bits
  • magnetic cores
  • punched cards, magnetic tape
• Hexadecimal numbers (Hex)
• Binary-Coded Decimal (BCD)
• ASCII
• Project 1

Mailing List, Homework, Lab

• Be sure you are signed up for the mailing list
• Lab hours:
  • Monday and Wednesday 2:30 to 5:45
  • Friday 10 to 4
• homework 1:
  • due Wednesday, September 3, in class (or email to esb@hawaii.edu before the start of class)
  • single-page answer (don't show calculations)
  • p. 16, exercise 1-8
  • p. 17, exercises 1-12, 1-15, 1-23
  • p. 18, exercises 1-31, 1-34
• Project 1:
  • due Friday, August 29, in the lab
  • http://www2.ics.hawaii.edu/~esb/2003fall.ics331/project1.html

Voltage, Current, and Resistance

• DC (Direct Current) voltage is fixed at a certain level, for example 5V
• some materials are insulators: even with a voltage applied, very little current flows (e.g. plastic, rubber, glass)
• some materials are conductors: with a voltage applied, strong current can flow (e.g. metal, impure water)
• some materials are semiconductors: they normally don't conduct, but an applied voltage can turn them into conductors

Resistors and LEDs

• A resistor is an electrical conductor that:
  • has known resistance (explained later)
  • can convert electrical energy to heat
• A Light-Emitting Diode (LED) is an electrical conductor that:
  • has variable resistance (the resistance depends on the applied voltage)
  • can convert electrical energy to light

Ohm's law

• Ohm's law: a resistor with resistance R and a voltage V applied to it has a current I flowing through it equal to: I = V/R
• Ohm () is the unit of resistance
• Volt (V) is the unit of voltage
• Amp (A) is the unit of current
• there must be a 10V voltage for a 10-mA current to flow through a 1K resistor
• if we have 5V across a 10K resistor, the current is 500uA
• voltage, current, and resistance can all be measured with a multimeter
• power is V I = V²/R = I² R. For example, 5V across 100 uses 0.25W.

In-class exercises

• I have a current of 1mA. How much resistance do I need to achieve a 5V voltage drop?
• a 100W, 110-volt light bulb has how much resistance? how much current does it consume?
• I have a 1K resistor designed to handle up to 1W. How much voltage can I put across it? What is the current at that voltage?

Series and Parallel Connections

• two resistors in series have the same current going through them. Therefore, the voltage across each resistor is proportional to the resistance
• two resistors in series have the same voltage across them. Therefore, the current through each resistor is inversely proportional to the resistance

Transistors

• a bipolar transistor is a component with three terminals:
  • an emitter (positive side -- source in an FET)
  • a collector (negative side -- drain in an FET)
  • a base (control side -- gate in an FET)
  

  a transistor (in saturation mode) is a switch:

  • a zero voltage at the base (or gate) results in no current flowing from the emitter to the collector (source to drain)
  • a high (5V) voltage at the base (or gate) results in lots of current flowing from the emitter to the collector (source to drain)

Transistor gates

• inverter (NOT gate)
• NAND gate
• NOR gate
• AND gate
• OR gate
• driving LEDs

Voltages as bits

• the circuits we will be using,
  • any voltage above 4.5V is a 1 bit
  • any voltage below 0.7V is a 0 bit
  • any other voltage is probably the consequence of a design or wiring error

Storage

• magnetic cores:
  • core is magnetized by a current
  • core retains magnetism after current stops
  • an erase pulse can erase the core
  • the magnetic field only changes if the core was magnetized
  • a change in the core's magnetic field is detected by a sense wire
• magnetic tape or disk:
  • spot on magnetic surface is magnetized
  • motion past head creates current proportional to magnetization
• punched cards

Hexadecimal Numbers

• 16 digits: 0..9 and A..F (or a..f)
• each hex digit corresponds to 4 bits
• conversion to and from decimal
• conversion to and from binary

Binary Coded Decimal

• 4 bits per decimal digit
• binary 0000 (for 0) to 1001 (for 9)
• arithmetic is a lot as for decimal numbers
• take more space than binary numbers

ASCII

• American Standard Code for Information Interchange
• standard encoding for letters, digits, and many symbols
• 7-bit code fits in a byte
• "A" is 0x41 (65), "Z" is 0x5A (90)
• "a" is 0x61 (97), "z" is 0x7A (122)
• "0" is 0x30 (48), "9" is 0x39 (57)
• " " (space) is 0x20 (32)
• man ascii on unix gives the translations