Intro to Electronics Week 2 Intro to Electronics, Week 2 Last - PowerPoint PPT Presentation

Intro to Electronics Week 2 Intro to Electronics, Week 2 Last updated Oct. 17, 2012 1

Build a simple power supply TODAY’S P PROJECT Intro to Electronics, Week 2 Last updated Oct. 17, 2012 2

BUT F FIRST: Intro to Electronics, Week 2 Last updated Oct. 17, 2012 3

How to measure what your circuit’s doing TEST E EQUIPMENT Intro to Electronics, Week 2 Last updated Oct. 17, 2012 4

Multimeter • Measures all kinds of things – Voltage – Current – Resistance – Other fancy things • Tests continuity • Some can give diode and transistor properties • etc. Intro to Electronics, Week 2 Last updated Oct. 17, 2012 5

Choosing a measurement Intro to Electronics, Week 2 Last updated Oct. 17, 2012 6

Try it on last week’s project • Measure voltage • Measure resistance of across resistor resistor Intro to Electronics, Week 2 Last updated Oct. 17, 2012 7

Try it on last week’s project • Measure current going into LED Intro to Electronics, Week 2 Last updated Oct. 17, 2012 8

Try it on last week’s project • When getting ready to measure current, look on the meter – Leads often have to be connected to different jacks than for voltage or resistance measurements Intro to Electronics, Week 2 Last updated Oct. 17, 2012 9

On to building new stuff POWER S SUPPLIES Intro to Electronics, Week 2 Last updated Oct. 17, 2012 10

The problem • Some circuits need specific voltages to work • Exact voltage we need isn’t always available • Solution: Convert what we have into what we need Intro to Electronics, Week 2 Last updated Oct. 17, 2012 11

Voltage divider • Easy way to get from one voltage to a lower voltage • Quick and dirty – Not too stable – Need to be able to predict your input voltage and output resistance • But it’s cheap! Intro to Electronics, Week 2 Last updated Oct. 17, 2012 12

The idea I ! !" ! = ! 1 + ! 2 R1 V out V in ! !"# = ! ∗ ! 2 R2 ! 2 ! !"# = ! !" ∗ ! 1 + ! 2 Intro to Electronics, Week 2 Last updated Oct. 17, 2012 13

Try it 1 ! ! Ω !"# = 6 ! ! ∗ ! 360 ! Ω + 1 ! ! Ω ! 360 � ! Out 6 V !"# = 4 . 4 ! ! ! 1 k � Intro to Electronics, Week 2 Last updated Oct. 17, 2012 14

Try it Intro to Electronics, Week 2 Last updated Oct. 17, 2012 15

Two problems • V out directly depends on V in – Unstable input = unstable output • If V out is connected to anything, it could change! – Why is this? Intro to Electronics, Week 2 Last updated Oct. 17, 2012 16

Combining resistances • Remember how batteries could be connected in series or in parallel? • Remember how they added up differently in each case? Intro to Electronics, Week 2 Last updated Oct. 17, 2012 17

Combining resistances • Series • Parallel 1 ! !"!#$ = ! ! + ! ! ! ! !"!#$ = ! ! ∥ ! ! = ! ! ! + 1 1 ! ! Intro to Electronics, Week 2 Last updated Oct. 17, 2012 18

What happens here? 360 � 6 V 1 k � ����� Intro to Electronics, Week 2 Last updated Oct. 17, 2012 19

What happens here? 1 ! ! Ω ! ∥ ! 220 ! Ω ! !"# = 6 ! ! ∗ 360 ! Ω + ( 1 ! ! Ω ! ∥ ! 220 ! Ω ) 1 ! ! Ω ! ∥ ! 220 ! Ω = ! 1 ! ! Ω ∗ 220 ! Ω 1 ! ! Ω + 220 ! Ω = 180 . 3 ! Ω 180 . 3 ! Ω 360 � 6 ! ! ∗ ! 360 ! Ω + 180 . 3 ! Ω = 2 ! ! 6 V 1 k � ����� :( Intro to Electronics, Week 2 Last updated Oct. 17, 2012 20

What else can we do? • Use a voltage regulator – Inexpensive (usually) chip – Handles all of this stuff for you Intro to Electronics, Week 2 Last updated Oct. 17, 2012 21

What else can we do? • Use a voltage regulator – Some are more complicated than others – Some let you set the output voltage you want – Some just lower voltage; others raise it Intro to Electronics, Week 2 Last updated Oct. 17, 2012 22

How do they work? • Details? Outside the scope of this class • But let’s find out how to use one! Intro to Electronics, Week 2 Last updated Oct. 17, 2012 23

Integrated circuits (ICs) • What people generally mean by “chip” • Usually black plastic with some metal pins http://en.wikipedia.org/wiki/ http://www.flickr.com/photos/ http://en.wikipedia.org/wiki/File:TO-220_ File:Three_IC_circuit_chips.JPG oskay/6328929468/ Package_Four_Different_Projections.jpg Intro to Electronics, Week 2 Last updated Oct. 17, 2012 24

Problem • They can sort of look the same http://www.flickr.com/photos/ ronybc/1713396200/ Intro to Electronics, Week 2 Last updated Oct. 17, 2012 25

Datasheet • Manufacturer’s instructions on how to use it • Can be a page or hundreds Intro to Electronics, Week 2 Last updated Oct. 17, 2012 26

Example Intro to Electronics, Week 2 Last updated Oct. 17, 2012 27

LM317 adjustable regulator • Adjustable – Easy to set — just add two resistors • Cheap (maybe $0.50) • Can regulate either voltage or current • Can take anywhere from 1.2 V to 37 V Intro to Electronics, Week 2 Last updated Oct. 17, 2012 28

LM317 adjustable regulator • Not very efficient – Good chance you’ll need a heatsink (We won’t in this class) Intro to Electronics, Week 2 Last updated Oct. 17, 2012 29

In the datasheet… http://www.ti.com/lit/ds/ symlink/lm117.pdf Intro to Electronics, Week 2 Last updated Oct. 17, 2012 30

In other words… !"# = 1 . 25 ! ! ∗ 1 + ! 2 ! ! 1 + 0 . 0001 ! ! ∗ ! 2 ! • V out doesn’t depend on V in ! Intro to Electronics, Week 2 Last updated Oct. 17, 2012 31

Try it Adj V in LM317 V out Out 360 � 6 V 1 k � !"# = 1 . 25 ! ! ∗ 1 + 1 ! ! Ω ! 360 ! Ω + 0 . 0001 ! ! ∗ 1 ! ! Ω = 4 . 82 ! V ! Intro to Electronics, Week 2 Last updated Oct. 17, 2012 32

Try it Intro to Electronics, Week 2 Last updated Oct. 17, 2012 33

Capacitors • Store energy in an electric field • Can be used to smooth out noisy signals • Also useful for: – Filters for audio and RF – Reaching high voltages Intro to Electronics, Week 2 Last updated Oct. 17, 2012 34

Capacitors • Some can be used in • Others blow up if you either direction put them in backward – These generally look – These generally look like discs like cans http:// http:// www.flickr.com/ www.flickr.com/ photos/ photos/ zero-waste/ dj-dwayne/ 4117130831/ 5584102517/ Intro to Electronics, Week 2 Last updated Oct. 17, 2012 35

Let’s add one Adj V in LM317 V out Out 360 � 6 V 0.1 µF 1 k � Intro to Electronics, Week 2 Last updated Oct. 17, 2012 36

The difference • Probably won’t notice one here – Battery powered, no load • Generally good practice – Helps keep things a bit more predictable – Datasheets can help provide guidance • LM317 said it’s useful on the input but unnecessary on the output Intro to Electronics, Week 2 Last updated Oct. 17, 2012 37

Oscilloscope • What if we want to look at the difference? • Oscilloscope shows voltage waveforms over time Volt ltage Time me Intro to Electronics, Week 2 Last updated Oct. 17, 2012 38

Oscilloscope • Sort of expensive – Hundreds of dollars to tens of thousands • Really handy, though Intro to Electronics, Week 2 Last updated Oct. 17, 2012 39

That’s it for tonight • Next week – Lights (both making and detecting) – Transistors – Maybe some digital logic Intro to Electronics, Week 2 Last updated Oct. 17, 2012 40