Introductory Electronics Pete Beens Westlane Secondary School Niagara Falls pete@beens.org teach Computer Engineering and Electronics

Why is this useful? You can do the extra credit lab for pts You may want to add a circuit to your final project You can do additional circuit labs as an alternate project (analog, digital) Electricity is mysterious, learning to understand it could come in handy some day!

Three Main Invisible Quantities Voltage, V, Volts Provides the “push” Current, I, Amperes (Amps) Flow of Electrons Amount of Current is dependent on Voltage and Resistance Resistance, R, Ohms (W) Limits the amount of current water tower analogy; height of tower is voltage, flow of water is current, tap is resistance

Safe Levels Voltage: 30 V Current: 5 mA (0.005 Amperes) Voltages inside a computer do not exceed 12 V, except at the power supply and power switch, which are at 120 V. Be careful in these areas! Current: 5 mA (0.005 Amperes)

Voltage Can Be Provided From… A battery

Voltage Can Be Provided From… Breadboard (trainer) See credits -- http://www.classictech.on.ca/ (London)

Current …is simply the flow of electrons Direction depends on convention Electron flow is from (-) to (+) (flow of electrons) Conventional flow is from (+) to (-) (hole flow) check start of chapter in textbook to check for current convention; this is important and must be defined when talking about direction of current flow refer to http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elecur.html for an excellent description

Resistors – Basic Specs Can be rated by… Resistance (Ohms, W) Tolerance (% of nominal value) Power Rating (Watts) Schematic Symbol…

Resistors – Types Variable (Potentiometer, Rheostat) Fixed variable resistors used to vary voltage (volume control) or current (LED intensity)

Resistors – Colour Code colour bands normally start towards one end Reproduced by permission of Tony van Roon, 2002 http://www.uoguelph.ca/~antoon

Resistors –Colour Code Example 3 102 5% (gold) 1st band: orange = 3 2nd band: orange = 3 3rd band: red = 2 (i.e. 102) 4th band: gold = 5% 33 x 102 = 3300 W = 3.3 k W

Resistors – Typical Power Ratings

Ohm’s Law “Current (I) is proportional to Voltage (V) and inversely proportional to Resistance (R)” UNITS: 1 Volt across 1 Ohm produces 1 Amp of current

Calculate the current in this circuit using Ohm’s Law 6V

Calculate the current in this circuit using Ohm’s Law 6V

Calculate the current in this circuit using Ohm’s Law 3V

Calculate the current in this circuit using Ohm’s Law 6V

How Many Volts across Resistor?

Ohm’s Law, Including Power Note that Power is also included in this chart Reproduced by permission of Tony van Roon, 2002 http://www.uoguelph.ca/~antoon

How Many Watts dissipated by Resistor? P=I2R

Kirchhoff’s Law’s Kirchhoff’s Voltage Law Kirchhoff’s Current Law “The sum of the voltage drops equals the applied voltage”, or… “The sum of the voltage drops around a closed loop equals zero” Used in series circuits Kirchhoff’s Current Law “The current entering a junction must equal the current leaving the junction” Use in parallel circuits.

Series Circuits One current path, therefore the current is the same everywhere Total resistance is the sum of the individual resistances

VOLTAGE DIVIDER I

Calculate RT and the current in this circuit, and v1 4 W 8 W v1 6V

Parallel Circuits More than one current path Total current is the sum of the individual currents

Parallel Circuits (2)

Calculate RT and the current in each branch of this circuit i1 i2 6 W 6 W 6V

Calculate RT and the current in each branch of this circuit i1 i2 6 W 3 W 6V

Calculate RT and the current in each branch of this circuit 3 W IT i1 i2 6V 6 W 6 W

CAPACITORS – DC I The capacitor charges linearly till the voltage across it reaches the applied voltage after which the driving force is lost and the capacitor ‘blocks’ DC.

RC CIRCUIT – DC - VC + This is similar but the capacitor charges non-linearly till the voltage across it reaches the applied voltage after which the driving force is lost. Time constant τ=1/RC is the time in which the capacitor is charged to 63% τ

RC CIRCUIT – DC After removing the battery, it discharges if there is a resistance in the external circuit (otherwise it retains the charge : use in DRAMs). The discharge is non-linear - VC(t) + I

DIODES If V > VON of diode, I I Forward bias, conducting Reverse bias, non conducting

N-Type Semiconductor P-Type Semiconductor

E E

Light Emitting Diodes A type of diode designed to emit light Can be visible or IR 2 V voltage drop Typically draws 20 mA (0.020 A) Schematic Symbol…

A Simple LED Circuit

Analyzing a LED Circuit with KVL and Ohm’s Law

The “Fuel Tank” Circuit 1) Charge the Fuel Tank

The “Fuel Tank” Circuit 2) Dis-Charge the Fuel Tank

Lab--The Breadboard Vin (6 V) Vss (Ground) Each row is Connected

Lab--A Simple Circuit Vin (6 V) Vss (Ground) Each row is Connected

Wire the following parallel circuit on the breadboard i1 i2 6 W 3 W 6V

The Parallel circuit from previous Vin (6 V) Vss (Ground)

A Series Circuit Vin (6 V) Vss (Ground)

Lab--Measure Volts in Parallel Because the voltmeter is placed in parallel with the circuit element, you do not need to physically alter your circuit in order to measure voltage.

Measure Voltage in Parallel Vin (6 V) Vss (Ground) V

Measure Current in Series You must physically modify your circuit: 1.Create a gap in the segment where you want to measure current. 2. Reconnect the gap using your ammeter as a jumper wire

Measure Current in Series Vin (6 V) Vss (Ground) A

Caution!!! If you measure Amps in parallel, you can damage the meter

Measure Resistance out of circuit Select the ohms mode, remove the resistor to be measured from your circuit, and place the ohmmeter leads across the resistor leads. It is not OK to use your fingers to do this (your body resistance will change result!)

Web References Learn Electronics Tutorials and Information Pages http://www.twysted-pair.com/ Electronics Tutorials http://www.electronics-tutorials.com/ Tutorials for Learning about Electronics http://www.iguanalabs.com/maintut.htm AC Electricity and Electronics http://www.sweethaven.com/acee/default.htm

Web References Jones on Stepper Motors Holt Software Tony’s Website http://www.cs.uiowa.edu/~jones/step/ Holt Software http://www.holtsoft.com/ Turing, Computer Engineering textbooks Tony’s Website http://www.uoguelph.ca/~antoon/ Many excellent tutorials, example circuits - and many others…