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

Intro to Electronics

Week 2

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

TODAY’S P PROJECT

Build a simple power supply

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

BUT F FIRST:

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 3

TEST E EQUIPMENT

How to measure what your circuit’s doing

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Multimeter

• Measures all kinds of things

– Voltage – Current – Resistance – Other fancy things

• Tests continuity
• Some can give diode and transistor properties
• etc.

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Choosing a measurement

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Try it on last week’s project

• Measure voltage

across resistor

• Measure resistance of

resistor

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Try it on last week’s project

• Measure current going into LED

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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

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POWER S SUPPLIES

On to building new stuff

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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

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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!

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! = !

!"

!1 + !2 !

!"# = ! ∗ !2

!

!"# = ! !" ∗

!2 !1 + !2

The idea

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 13

Vin Vout R1 R2 I

!"# = 6!! ∗! 1!!Ω 360!Ω + 1!!Ω! ! !"# = 4.4!!!

Try it

6 V 360 1 k

Out

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Try it

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Two problems

• Vout directly depends on Vin

– Unstable input = unstable output

• If Vout is connected to anything, it could

change!

– Why is this?

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Combining resistances

• Remember how batteries could be

connected in series or in parallel?

• Remember how they added up differently in

each case?

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Combining resistances

• Series
• Parallel

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!!"!#$ = !! + !!!

!!"!#$ = !! ∥ !! = 1 1 !! + 1 !! !

What happens here?

6 V 360 1 k

• Last updated Oct. 17, 2012

Intro to Electronics, Week 2 19

!

!"# = 6!! ∗

1!!Ω! ∥ !220!Ω 360!Ω + (1!!Ω! ∥ !220!Ω) 1!!Ω! ∥ !220!Ω =! 1!!Ω ∗ 220!Ω 1!!Ω + 220!Ω = 180.3!Ω 6!! ∗! 180.3!Ω 360!Ω + 180.3!Ω = 2!!

What happens here?

6 V 360 1 k

• Last updated Oct. 17, 2012

Intro to Electronics, Week 2 20

:(

What else can we do?

• Use a voltage regulator

– Inexpensive (usually) chip – Handles all of this stuff for you

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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

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How do they work?

• Details? Outside the scope of this class
• But let’s find out how to use one!

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Integrated circuits (ICs)

• What people generally mean by “chip”
• Usually black plastic with some metal pins

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 24 http://en.wikipedia.org/wiki/ File:Three_IC_circuit_chips.JPG http://www.flickr.com/photos/

• skay/6328929468/

http://en.wikipedia.org/wiki/File:TO-220_ Package_Four_Different_Projections.jpg

Problem

• They can sort of look the same

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 25 http://www.flickr.com/photos/ ronybc/1713396200/

Datasheet

• Manufacturer’s instructions on how to use it
• Can be a page or hundreds

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Example

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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

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LM317 adjustable regulator

• Not very efficient

– Good chance you’ll need a heatsink (We won’t in this class)

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In the datasheet…

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http://www.ti.com/lit/ds/ symlink/lm117.pdf

!

!"# = 1.25!! ∗ 1 + !2

!1 + 0.0001!! ∗ !2!

In other words…

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 31

• Vout doesn’t depend
• n Vin!

Try it

6 V 360 1 k

Adj Vin Vout Out LM317

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 32

!

!"# = 1.25!! ∗ 1 + 1!!Ω

360!Ω + 0.0001!! ∗ 1!!Ω = 4.82!V!

Try it

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

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Capacitors

• Some can be used in

either direction

– These generally look like discs

• Others blow up if you

put them in backward

– These generally look like cans

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 35 http:// www.flickr.com/ photos/ dj-dwayne/ 5584102517/ http:// www.flickr.com/ photos/ zero-waste/ 4117130831/

Let’s add one

6 V 360 1 k

Adj Vin Vout Out LM317

0.1 µF

Last updated Oct. 17, 2012 Intro to Electronics, Week 2 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
• n the output

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Oscilloscope

• What if we want to look at the difference?
• Oscilloscope shows voltage waveforms
• ver time

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Time me Volt ltage

Oscilloscope

• Sort of expensive

– Hundreds of dollars to tens of thousands

• Really handy, though

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That’s it for tonight

• Next week

– Lights (both making and detecting) – Transistors – Maybe some digital logic

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