Practical Electronics - Lecture 3

00:52:11
https://www.youtube.com/watch?v=VoPoZn7ThkA

摘要

TLDRLa classe comença amb anuncis sobre les assignatures properes, incloent-hi la primera tasca i el primer laboratori. Els estudiants formaran parelles per al laboratori, on començaran a dissenyar i construir una estructura de prova per a un projecte de hèlix a velocitat constant. La sessió inclou una revisió de la teoria del circuit i les seves aplicacions pràctiques, enfocant-se en la resistència del filferro i el seu impacte, com en l'eficiència dels panells solars. També es presenten components reactius, com condensadors i inductors, i les seves aplicacions pràctiques en circuits, com ara la reducció de soroll amb condensadors de desconnexió. La importància del calibre del fil es destaca pel seu impacte en la resistència i l'eficiència del circuit.

心得

  • 📅 Consulteu la pàgina Canvas per a les assignatures properes.
  • 🔬 Formar grups de dos per al laboratori de divendres.
  • 💡 La resistència del fil és crucial en aplicacions pràctiques com els panells solars.
  • ⚙️ Utilitzeu condensadors de desconnexió per reduir el soroll del circuit.
  • 📏 El calibre del fil afecta l'eficiència del circuit.
  • 🔋 El projecte inclou una estructura de prova per a una hèlix de velocitat constant.
  • 🔧 El passat per alt canvia el comportament en el disseny del circuit.
  • 💬 Les hores de despatx comencen immediatament després de la classe.
  • 📖 Utilitzeu els recursos del taller itll per a tutorials addicionals.
  • 📝 Els condensadors bloquegen efectivament el soroll en senyals DC.

时间轴

  • 00:00:00 - 00:05:00

    La classe comença amb anuncis sobre les properes tasques i la formació de grups per a un projecte de propulsor de velocitat constant. Es revisarà la teoria de circuits inicial, centrant-se en aplicacions pràctiques, incloent resistència de filferros.

  • 00:05:00 - 00:10:00

    Es discuteix la importància de la medició precisa de la resistència de cables en projectes, especialment amb corrents elevats, per evitar caigudes de tensió significatives que poden afectar els resultats.

  • 00:10:00 - 00:15:00

    S'explica com calcular la resistència del cable basant-se en la resistivitat del metall, la longitud i l'àrea de secció transversal, amb exemples pràctics de coure versus alumini.

  • 00:15:00 - 00:20:00

    S'ofereix un exemple amb un sistema de panells solars i el càlcul de la pèrdua de potència dels cables a causa de la resistència, destacant la importància de l'elecció del calibre del cable.

  • 00:20:00 - 00:25:00

    Un altre exemple mostra les implicacions pràctiques de seleccionar cables de diferent calibre, analitzant la pèrdua de potència i d'eficiència en sistemes de potència alimentats per energia solar.

  • 00:25:00 - 00:30:00

    Discutir sobre la configuració en sèrie versus paral·lel per als panells solars i com pot reduir la pèrdua de potència considerablement, mostrant l'eficàcia d'utilitzar tensions més altes.

  • 00:30:00 - 00:35:00

    S'explica la llei d'Ohm i s'introdueixen conceptes de components reactius com capacitors i inductors, i la seva importància en aplicacions pràctiques com el filtratge del soroll en circuits.

  • 00:35:00 - 00:40:00

    Es presenten diferents tipus de capacitors i les seves aplicacions, incloent la descripció detallada de les capacitats d'acoblament i desacoblament de soroll, utilitzant exemples pràctics.

  • 00:40:00 - 00:45:00

    Es discuteix sobre el paper dels inductors en el bloqueig de freqüències amb AC i el seu ús en diferents circuits amb exemples específics i variats de disseny d'inductors.

  • 00:45:00 - 00:52:11

    La classe conclou amb recordatoris sobre les tasques properes i l'horari de laboratori, destacant la importància de les capacitats pràctiques com la soldadura i el treball amb microcontroladors.

显示更多

思维导图

视频问答

  • What are the upcoming assignments?

    Check the Canvas page for details on upcoming assignments, including homework and a lab session.

  • How are groups formed for the lab?

    Groups of two are formed for the first lab, focusing on designing and building a test bed structure.

  • What is the purpose of discussing wire resistance?

    To illustrate its practical importance, especially in applications like solar panels and circuits, where it affects efficiency.

  • What are decoupling capacitors used for?

    To reduce noise from external sources in electronic circuits by providing a low impedance path to ground.

  • Why is wire gauge important?

    Wire gauge affects resistance, which impacts efficiency and power loss, especially at higher currents.

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  • 00:00:00
    [Music]
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    [Applause]
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    [Music]
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    good afternoon everybody let's get
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    started with the class so I am doubly
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    remote today so if you have any problems
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    seeing anything uh I'm putting on the
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    screen please let me know shoot me a
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    chat if I don't see your chat please
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    Shout It Out by
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    unmuting so for announcements uh please
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    see the canvas page for the upcoming
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    assignments you have a homework one
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    coming up soon that due date and due
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    time are posted there uh lab one the
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    first lab will be this Friday and you
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    will form groups of two so you'll have
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    one one uh lab partner and you'll start
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    uh designing and building your uh test
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    bed structure for the constant speed
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    propeller project that we're going to
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    talk about I'll give you an overview of
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    that uh this Friday in
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    lab um so let's get started on the
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    material during the last class I started
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    off with a review we're going to spend a
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    couple more lectures on review I want to
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    make sure you have a good foundation on
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    um some of the original or initial
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    circuit theory that you've seen before
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    but show you some practical applications
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    especially when you might run into some
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    of these problems during your project or
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    future
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    projects um and uh we're going to let's
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    see last time we talked about circuit
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    Theory we focused on some applications
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    we ended with
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    calculating energy uh delivered to a
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    device and we also talked about
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    resistance of a wire and I want to show
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    you a practical application of that
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    today with with solar panels and power
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    efficiency
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    so so last time we talked
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    about um wire resistance and I mentioned
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    how well wires aren't ideal and you're
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    always going to have some resistance and
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    sometimes that matters and sometimes you
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    actually have to measure some really low
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    resistance values we saw this last year
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    during the project when we bought some
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    uh breadboards and actually a lot of
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    breadboards will do this if you if you
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    try to have more than a few
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    milliamps uh run through the the the
  • 00:02:38
    blades of a breadboard uh you might see
  • 00:02:40
    significant voltage drops we were seeing
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    that last year which is why we're going
  • 00:02:44
    to a printed circuit board this year
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    you'll see those in lab this year but
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    let's suppose you have this uh wire
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    under
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    test uh when you measure a wire the
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    problem is that you also have wires
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    coming from the the test test leads that
  • 00:03:00
    have may have their own resistance and
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    they contribute to voltage drops
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    especially when you have higher current
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    if you're just dealing with a few
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    milliamps that's usually not a big deal
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    once you get up into the amp range or
  • 00:03:13
    higher then some of these thinner gauge
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    wires can have cause a problem so let's
  • 00:03:18
    suppose you have a a power supply set
  • 00:03:21
    for constant current here it's set for
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    uh 2 amps current and I connect test
  • 00:03:28
    leads to this wire um then what what I
  • 00:03:32
    would do and what I did for measuring
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    voltage across this wire is take the
  • 00:03:37
    voltmeter and connect it directly across
  • 00:03:39
    the wire because what you'll see is that
  • 00:03:41
    although there's uh1 128 volts across
  • 00:03:46
    the wire if you go back to the other
  • 00:03:50
    side of the test leads we have 04 volts
  • 00:03:53
    measured with a volt
  • 00:03:55
    meter okay so that um
  • 00:04:00
    uh means that there's uh a drop a
  • 00:04:02
    voltage drop there across the test lead
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    so.
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    232 roughly voltage drop is across the
  • 00:04:10
    the the test
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    leads okay and that's actually more than
  • 00:04:13
    the voltage across the wire you're
  • 00:04:15
    trying to test so that's going to give
  • 00:04:17
    you a a bad measurement and a bad
  • 00:04:21
    calculation of wire
  • 00:04:24
    resistance so the point here is
  • 00:04:27
    that uh notice that where you measure
  • 00:04:30
    voltage matters especially when dealing
  • 00:04:32
    with higher current uh and I'm going to
  • 00:04:35
    call out when we get to test equipment
  • 00:04:39
    that measures resistance that there's
  • 00:04:41
    actually a four-wire test where you have
  • 00:04:44
    to use four leads connected to the m
  • 00:04:46
    meter in order to get a good measurement
  • 00:04:48
    of a of a low resistance
  • 00:04:52
    load and notice here that some power
  • 00:04:54
    supplies like this one
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    have voltage uh measurements and current
  • 00:05:00
    measurements and often times they're
  • 00:05:02
    either not so accurate they're not as
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    accurate as a
  • 00:05:06
    voltmeter or an ammeter that's designed
  • 00:05:09
    to be a voltmeter or an ammeter um or
  • 00:05:12
    sometimes there's resistance internally
  • 00:05:14
    or in the junction to the test leads
  • 00:05:16
    that causes a voltage drop so measuring
  • 00:05:21
    or where you measure voltage matters in
  • 00:05:24
    high current situations and high current
  • 00:05:27
    again is if you're using thin test leads
  • 00:05:30
    then an amp or above
  • 00:05:36
    matters okay
  • 00:05:38
    so this voltage drop comes from
  • 00:05:41
    resistivity of the material used for the
  • 00:05:44
    wire so the resistance of a wire can be
  • 00:05:47
    calculated um and characterized using a
  • 00:05:50
    resistivity value called
  • 00:05:53
    row um it's in units of ohm
  • 00:05:57
    meters and so if you have
  • 00:06:00
    have a wire of length L and that wire is
  • 00:06:05
    made of a a metal with resistivity row
  • 00:06:10
    here's the resistance R in ohms
  • 00:06:12
    resistivity Row in ohm meters length and
  • 00:06:15
    meters cross-sectional area and meter
  • 00:06:17
    squared the resistance of that wire is
  • 00:06:20
    row L over
  • 00:06:22
    a it's kind of what you would expect
  • 00:06:24
    right because you would think that the
  • 00:06:27
    longer a wire is the higher the
  • 00:06:29
    resistance
  • 00:06:30
    would be and the thinner a wire is or
  • 00:06:34
    lower cross-sectional area higher the
  • 00:06:37
    resistance would be and that that's
  • 00:06:39
    reflected here in this relationship
  • 00:06:43
    shown so resistivity is a characteristic
  • 00:06:47
    of the metal it's it's it's um it
  • 00:06:50
    depends on the
  • 00:06:51
    material and what you'll see is uh in
  • 00:06:55
    the past there was a lot of wire that
  • 00:06:57
    was just copper but you'll see now
  • 00:07:00
    there's some wire that's copper coded
  • 00:07:02
    aluminum and basically it makes it uh
  • 00:07:04
    cheaper to produce and aluminum has uh a
  • 00:07:08
    worse resistivity it's a higher
  • 00:07:11
    resistivity compared to Copper so you
  • 00:07:12
    got to pay attention to what kind of
  • 00:07:14
    material you're using uh or what what
  • 00:07:17
    kind of material the wire is made of
  • 00:07:20
    when you're calculating resistivity and
  • 00:07:22
    you're trying to figure out what is the
  • 00:07:24
    voltage drop between your power source
  • 00:07:26
    and the load
  • 00:07:30
    the resistivity of copper is this uh
  • 00:07:33
    1.72 *
  • 00:07:35
    108 ohm meters and that's at at 20
  • 00:07:38
    degrees C I'll show you some information
  • 00:07:41
    on
  • 00:07:44
    that so here's an example if you have a
  • 00:07:47
    th000 feet of copper
  • 00:07:50
    wire and it's a 12 gauge wire we'll talk
  • 00:07:53
    about 12 gauge wire um it has a diameter
  • 00:07:56
    of uh 0.08 oh
  • 00:08:00
    in and so let's calculate the resistance
  • 00:08:03
    of that wire so here's the
  • 00:08:05
    resistivity there's the copper wire
  • 00:08:07
    resistivity length is 1,000 feet let's
  • 00:08:10
    convert that to
  • 00:08:12
    meters uh the wire diameter is 80 Ms
  • 00:08:16
    80.8 Ms 80.8
  • 00:08:18
    th000 all right that's the value in
  • 00:08:22
    meters so the area is this in meter
  • 00:08:25
    squared and that means um row L over a
  • 00:08:29
    is 1.5 ohms so you get about 1.5 1.6
  • 00:08:32
    ohms of resistance across this 12 gauge
  • 00:08:35
    wire which again can be a problem if you
  • 00:08:38
    have high current going through that
  • 00:08:41
    wire
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    okay so that's the resistance um per th
  • 00:08:47
    feet you can calculate for this wire and
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    then you can scale from
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    there for your
  • 00:08:54
    application it's common to give
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    wire resistance in ohms per thousand
  • 00:09:01
    feet so you don't have to use the
  • 00:09:03
    property of the material you can just
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    look at the specification for the
  • 00:09:06
    wire okay you will
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    see especially when I well I'll show you
  • 00:09:13
    a table of wire gauges but uh some
  • 00:09:16
    equations use circular Mills and that's
  • 00:09:19
    a constant that um accounts for the
  • 00:09:23
    resistivity and the length units
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    specifically the ratio of um area
  • 00:09:27
    between a square and a circle make life
  • 00:09:29
    easier so you'll see this sometimes if
  • 00:09:31
    you're given circular Mills you get a
  • 00:09:35
    constant you get an area in circular
  • 00:09:37
    Mills and a length in feet and this is
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    how you calculate resistance of a wire
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    given those
  • 00:09:42
    parameters but I don't see that that
  • 00:09:44
    often but you will see it in the table I
  • 00:09:46
    show you
  • 00:09:51
    next okay so here's wire gauge this is
  • 00:09:54
    this applies this wire gauge table I'm
  • 00:09:56
    going to show you is American wire gauge
  • 00:09:58
    it applies here in the states uh
  • 00:10:01
    International versions may vary but we
  • 00:10:03
    use AWG here sometimes just called
  • 00:10:06
    gauge so a common way to
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    specify uh the
  • 00:10:12
    diameter um of of a uh a solid round
  • 00:10:18
    electrical wire is with Gauge American
  • 00:10:20
    wire gauge okay you'll see resistance in
  • 00:10:23
    tables associated with those
  • 00:10:26
    gauges and they typically specify like
  • 00:10:29
    we calculated on the last slide ohms per
  • 00:10:31
    th000 ft at various temperatures right
  • 00:10:34
    there's a difference if you have
  • 00:10:35
    a copper outside versus copper under the
  • 00:10:38
    hood of a car which is much different
  • 00:10:41
    temperature here's a table you can find
  • 00:10:43
    these tables in various
  • 00:10:46
    forms but on the left you see the wire
  • 00:10:50
    gauge right here's 0 1 two 3 4 as you go
  • 00:10:53
    up in number on wire gauge the wire gets
  • 00:10:56
    thinner as you go down the wire gets
  • 00:10:59
    thicker and if you want Thicker Than
  • 00:11:01
    Zero you go to double or triple A or
  • 00:11:04
    quadruple a okay so then here you'll see
  • 00:11:08
    diameter in Mills Mills um is a
  • 00:11:11
    thousandth of an inch right so I will
  • 00:11:13
    use Mills and um thousands
  • 00:11:18
    interchangeably here's that circular
  • 00:11:20
    Mills
  • 00:11:21
    unit uh square inches and then here
  • 00:11:23
    along the top you have temperature and
  • 00:11:26
    then the uh resistance per th F feet for
  • 00:11:30
    those temperature columns and for
  • 00:11:32
    example a 14 gauge
  • 00:11:33
    wire um has let's see it is it's its
  • 00:11:37
    diameter 64 Ms so
  • 00:11:42
    64,000 and that's the
  • 00:11:45
    area and so at 20 C it's 2.5 ohms per th
  • 00:11:52
    feet okay so room temperature that's
  • 00:11:54
    what the resistance is and resistance
  • 00:11:56
    increases with with temperature
  • 00:12:01
    okay so so then this is for solid wire
  • 00:12:04
    or uh stranded wire if you're using that
  • 00:12:07
    then the cross-sectional area is the
  • 00:12:09
    equivalent area of that of a solid
  • 00:12:11
    copper wire so the stranded wire is
  • 00:12:13
    going to
  • 00:12:14
    be a larger diameter for the same
  • 00:12:17
    resistance per thousand feet for the
  • 00:12:19
    same
  • 00:12:21
    gauge
  • 00:12:24
    okay all right so let's talk about a
  • 00:12:27
    practical example this is like ohms and
  • 00:12:29
    tables and you know why does this matter
  • 00:12:33
    well here's an example that I actually
  • 00:12:36
    ran into um and if you ever go off- Grid
  • 00:12:40
    or install a uh an array of solar panels
  • 00:12:43
    on your house or wherever right your
  • 00:12:46
    cabin then then you will likely run into
  • 00:12:49
    this issue let's suppose for example you
  • 00:12:53
    have four solar
  • 00:12:55
    panels okay and then you have a load you
  • 00:12:57
    want to power this load with a
  • 00:12:59
    uh with a solar panel
  • 00:13:01
    controller solar panel controller does
  • 00:13:04
    lots of things it it takes in a wide
  • 00:13:07
    range of of voltage from the solar panel
  • 00:13:09
    and it outputs usually a charging
  • 00:13:12
    voltage for a battery and then the
  • 00:13:15
    battery connects to the loads or or a
  • 00:13:18
    power inverter which converts the DC
  • 00:13:20
    battery voltage to um AC for AC
  • 00:13:26
    loads okay and let's suppose that load
  • 00:13:30
    is uh 50 ft away from the solar
  • 00:13:34
    panels and maybe these wires run down
  • 00:13:37
    the house or they run uh from uh you
  • 00:13:41
    know your your uh your cabin or your uh
  • 00:13:44
    your off-grid camping trailer is in the
  • 00:13:46
    shade and you're 50 feet away so this is
  • 00:13:49
    a reasonable
  • 00:13:50
    distance okay and you're decid you're
  • 00:13:52
    trying to decide on wire gauge and you
  • 00:13:55
    know in circuits class it doesn't matter
  • 00:13:57
    right you just all wires are perfect
  • 00:14:00
    conductors and so you'll see it matters
  • 00:14:03
    here so each panel is um nominally 100
  • 00:14:07
    Watts at 18 volts for this particular
  • 00:14:09
    panel that I chose and that's that's uh
  • 00:14:13
    the um Sun's power roughly and just
  • 00:14:17
    bright Sun roughly it's a a kilowatt per
  • 00:14:20
    square meter at 20% 23% you get about
  • 00:14:23
    200 Watts out of a square meter and so
  • 00:14:26
    this is probably a half square meter
  • 00:14:28
    panel
  • 00:14:29
    with a voltage of 18
  • 00:14:33
    volts and there's various ways you can
  • 00:14:36
    connect solar panels together and one
  • 00:14:39
    way is to put them all in parallel so if
  • 00:14:40
    I have 18
  • 00:14:43
    volts at each of these uh panels
  • 00:14:45
    terminals I can connect them all in
  • 00:14:47
    parallel and so I'm joining all 18 volts
  • 00:14:50
    right all panels together producing 18
  • 00:14:52
    volts here that's a reasonable way to do
  • 00:14:54
    it you can do
  • 00:14:56
    that um and so each panel will
  • 00:14:59
    contribute current which will flow out
  • 00:15:02
    of each of its red leads the positive
  • 00:15:04
    leads down to the power uh to the um
  • 00:15:07
    charge controller and then back to the
  • 00:15:11
    panel okay and so you have if you have
  • 00:15:15
    four 100 watt panels you have 400 watts
  • 00:15:18
    total at 18
  • 00:15:21
    volts so the question becomes well you
  • 00:15:23
    know we talked about high current is a
  • 00:15:25
    problem through thin gauge
  • 00:15:27
    wire um here you have a current of 22
  • 00:15:31
    amps so you have 400 watts at 18 volts
  • 00:15:34
    so you know voltage changes depending
  • 00:15:37
    upon solar conditions and how much load
  • 00:15:38
    you apply to the solar panel but let's
  • 00:15:40
    use this as a rough estimate of uh 22
  • 00:15:44
    amps you have 22 amps coming from those
  • 00:15:47
    panels going to the right through the
  • 00:15:50
    red wire black uh to the left through
  • 00:15:52
    the black wire supplying your charge
  • 00:15:54
    controller and load and let's suppose
  • 00:15:57
    the charge controller maximum input
  • 00:15:59
    voltage is 100
  • 00:16:01
    volts typically these charge controllers
  • 00:16:03
    have some Maximum voltage you go higher
  • 00:16:05
    than that you destroy
  • 00:16:08
    them okay now you're you're choosing
  • 00:16:11
    wire and so you're looking at um this uh
  • 00:16:15
    7 $72 for 50 feet of wire red black wire
  • 00:16:19
    it's meant for a solar installation and
  • 00:16:22
    it's 14
  • 00:16:23
    gauge okay and so let's figure out well
  • 00:16:28
    is this going to work work and what do I
  • 00:16:29
    mean by work it means are you going to
  • 00:16:32
    waste all of your power or how much of
  • 00:16:34
    your power are you going to waste
  • 00:16:36
    because of the resistance of the wire
  • 00:16:38
    you're actually just heating up the wire
  • 00:16:40
    instead of delivering the energy to the
  • 00:16:42
    load where you want it to
  • 00:16:45
    be so here's the uh here's the
  • 00:16:48
    resistance per length from the table 14
  • 00:16:50
    gauge wire 2.5 ohms per th000 feet we
  • 00:16:54
    have 100 fet of wies so it's only 50
  • 00:16:56
    feet away but we have two lengths of 50t
  • 00:16:59
    so that current has to travel
  • 00:17:04
    100t and all 100t will be heating
  • 00:17:08
    up okay the resistance then is a a
  • 00:17:11
    quarter ohm that doesn't seem that bad
  • 00:17:13
    you have a quarter ohm resistance that
  • 00:17:16
    should be just fine
  • 00:17:18
    right but when you have a current of 22
  • 00:17:21
    amps um the power loss to the wire is
  • 00:17:24
    actually
  • 00:17:25
    127 uh Watts that's huge
  • 00:17:30
    and the power from the panel if it's 400
  • 00:17:32
    watts you're actually losing 32% of your
  • 00:17:34
    power to the
  • 00:17:36
    wire that's a lot right big percentage
  • 00:17:40
    of your power is not going to the load
  • 00:17:41
    where you want it to
  • 00:17:43
    be so let's suppose you browse around
  • 00:17:45
    some more online and you find this $140
  • 00:17:48
    wire which is 10 gauge right it's almost
  • 00:17:50
    twice the
  • 00:17:52
    price and here's the resistance per
  • 00:17:55
    length of that 10 gauge
  • 00:17:57
    wire right
  • 00:18:00
    and so you still have 100
  • 00:18:03
    feet and the resistance then of that
  • 00:18:06
    wire is point1 ohms well that's less
  • 00:18:08
    that's good right instead of a quarter
  • 00:18:09
    ohm you're a tenth of an OHM but you
  • 00:18:11
    still have that same current 22 amps so
  • 00:18:15
    the power loss to the wire
  • 00:18:17
    is uh
  • 00:18:20
    50.3 Watts that's still a lot of power
  • 00:18:23
    right you're losing a lot of power to
  • 00:18:25
    metal which is supposed to be a perfect
  • 00:18:26
    conductor in our circuits class it's not
  • 00:18:30
    so this is something to consider but
  • 00:18:33
    it's less power loss so we have 400
  • 00:18:36
    watts from the panel that means only 13%
  • 00:18:39
    of that power is lost to the
  • 00:18:43
    wire okay so the whole point of this
  • 00:18:46
    exercise the slide I'm showing up is
  • 00:18:48
    that um wire resistance matters at this
  • 00:18:52
    higher of current and longer distances
  • 00:18:57
    so if you have some project where you
  • 00:18:58
    have a power supply that needs to be far
  • 00:19:00
    away from its load and you need a
  • 00:19:03
    certain voltage at that other end where
  • 00:19:04
    the load is you have to consider the
  • 00:19:06
    voltage drop and if it's a portable or
  • 00:19:09
    battery powered or solar powerered
  • 00:19:11
    application power
  • 00:19:13
    lost uh power power lost to heat in the
  • 00:19:16
    wires A
  • 00:19:17
    consideration but so great let's use the
  • 00:19:20
    largest possible wire we can well
  • 00:19:23
    there's disadvantages to that
  • 00:19:25
    because um that wire is more more
  • 00:19:29
    expensive right so you think about it
  • 00:19:31
    what would your decision be would you
  • 00:19:33
    would you go cheaper on the wire and
  • 00:19:36
    give away
  • 00:19:37
    32% well that means you paid for
  • 00:19:41
    32% too many solar panels right so you
  • 00:19:45
    actually paid your part of your solar
  • 00:19:47
    array is just going to heat up heat up
  • 00:19:49
    the wire and you bought it to heat up
  • 00:19:51
    the wire or you go with a more expensive
  • 00:19:54
    wire and have a better power efficiency
  • 00:19:57
    so there's no right answer here it's
  • 00:19:59
    just going to make that decision as an
  • 00:20:02
    engineer um your decision might be
  • 00:20:05
    different if this is a 4 kilowatt system
  • 00:20:07
    right if you had 40 panels instead of
  • 00:20:08
    four panels right that's that's a lot of
  • 00:20:11
    power loss panels are
  • 00:20:14
    expensive you know so again it's just
  • 00:20:17
    I'm just showing you some inputs to a
  • 00:20:19
    trade you might
  • 00:20:21
    make and also cost isn't only a factor
  • 00:20:24
    weight and temperature are are factors
  • 00:20:27
    um if you have
  • 00:20:29
    uh a you know higher temperature like I
  • 00:20:33
    don't know it's in the desert versus um
  • 00:20:36
    up up farther north you might have
  • 00:20:39
    higher res uh resistivity at Peak Sun
  • 00:20:43
    Times which is when you want the solar
  • 00:20:45
    panels to be
  • 00:20:46
    operating and uh weight is consideration
  • 00:20:49
    so if this were an aircraft
  • 00:20:52
    application and you care about
  • 00:20:54
    delivering power from an alternator to a
  • 00:20:56
    battery to the rest of the avionics or
  • 00:20:58
    or other power Power Systems um than uh
  • 00:21:01
    than you would
  • 00:21:02
    care
  • 00:21:05
    um so uh so wait wait you know and you
  • 00:21:08
    don't want an airplane to get heavier
  • 00:21:10
    because then you're carrying you're
  • 00:21:11
    reducing your payload to your
  • 00:21:13
    airplane so you gota again you got to
  • 00:21:16
    make you got to figure out what what all
  • 00:21:17
    the trades are it's not just cost and
  • 00:21:19
    power loss it's also weight temperature
  • 00:21:21
    and other things so why does the
  • 00:21:23
    resistance of a wire change with
  • 00:21:25
    temperature yeah so um
  • 00:21:29
    basically the resistivity goes up and
  • 00:21:32
    without going into the um the physics
  • 00:21:34
    too much of that uh you get you get high
  • 00:21:38
    higher electron motion when the um the
  • 00:21:41
    wire gets hot and the
  • 00:21:44
    resistivity uh uh goes up and that's
  • 00:21:48
    going to be result in a higher
  • 00:21:51
    resistance for the overall
  • 00:21:55
    wire okay
  • 00:22:00
    so okay great so you have
  • 00:22:02
    that and then you want to
  • 00:22:07
    um what's an alternative right so let's
  • 00:22:09
    let's figure out an alternative to this
  • 00:22:11
    because you're you're still losing a
  • 00:22:13
    whole lot of power in The Wire so what
  • 00:22:16
    else can we do here we have the same
  • 00:22:18
    four solar panels you have the same load
  • 00:22:22
    the same charge
  • 00:22:24
    controller the same length of
  • 00:22:26
    wire um and each panel is still 100
  • 00:22:30
    Watts at 18
  • 00:22:31
    volts but instead of connecting these
  • 00:22:34
    power uh panels in
  • 00:22:36
    parallel let's
  • 00:22:38
    connect these uh panels in in
  • 00:22:42
    series okay so let's do
  • 00:22:45
    this right let's connect all these in
  • 00:22:47
    series and so this is like
  • 00:22:51
    connecting uh sources voltage sources in
  • 00:22:54
    series so you run the kvl equation
  • 00:22:56
    around this and you get 72 volts between
  • 00:22:58
    these two wires so it's no longer 18 you
  • 00:23:01
    have 72
  • 00:23:02
    volts at that connection to the end of
  • 00:23:05
    The
  • 00:23:06
    Wire so now you have 400 watts still
  • 00:23:09
    there're still 400 watt solar panels but
  • 00:23:12
    you're operating at um at 72 volts so
  • 00:23:17
    your current is not 20 amps or 22 amps
  • 00:23:20
    it's down to 5 and a half
  • 00:23:23
    amps okay uh so will this destroy the
  • 00:23:26
    control or no because controller this
  • 00:23:29
    particular controller handles 100 volts
  • 00:23:31
    so you'll see controllers that handle
  • 00:23:33
    around 100 volts some are a lot lower
  • 00:23:35
    but many control solar charge
  • 00:23:38
    controllers will handle
  • 00:23:40
    that okay so let's go grab the same wire
  • 00:23:43
    and see what happens here you have uh
  • 00:23:46
    same resistance per length the same
  • 00:23:49
    length here's the resistance same
  • 00:23:51
    resistance the current now is not 22
  • 00:23:53
    amps it's uh five amps so the power lost
  • 00:23:57
    to the wire
  • 00:23:59
    uh is now 7.9
  • 00:24:02
    watts and that's only
  • 00:24:04
    2% power
  • 00:24:07
    loss okay so here for 10 gauge
  • 00:24:10
    wire here's the resistance per length 10
  • 00:24:13
    gauge wire same
  • 00:24:14
    length here's the resistance the current
  • 00:24:17
    again is uh five and a half
  • 00:24:20
    amps okay and the power loss to the wire
  • 00:24:24
    there is 3.1 Watts which is only 1%
  • 00:24:29
    so just by changing the configuration of
  • 00:24:31
    those solar panels from parallel to
  • 00:24:34
    series dropped the power loss to the
  • 00:24:38
    wire uh by a huge
  • 00:24:40
    amount right our power efficiency got a
  • 00:24:42
    lot
  • 00:24:43
    better and now the difference between 14
  • 00:24:46
    gauge and 10 gauge wire is only 1% right
  • 00:24:49
    2% 1% it's 1% difference so maybe maybe
  • 00:24:54
    it's not worth the more expensive wire
  • 00:24:55
    right so in the other case it might have
  • 00:24:57
    been worth
  • 00:24:59
    the more expensive wire the heavier
  • 00:25:02
    wire so the um higher voltage that you
  • 00:25:07
    use for power transmission is generally
  • 00:25:10
    more efficient because you have lower
  • 00:25:13
    current needed so that's why you see
  • 00:25:16
    these high voltage power lines up really
  • 00:25:18
    high off the ground and they're you know
  • 00:25:20
    700 kilovolts um as various voltages but
  • 00:25:25
    um that lets you deliver
  • 00:25:29
    the same amount of power at a lower
  • 00:25:31
    current because you're using higher
  • 00:25:33
    voltage that's the whole premise here
  • 00:25:36
    right so why don't you just use high
  • 00:25:37
    voltage everywhere just let's let's keep
  • 00:25:39
    going up in voltage well it becomes very
  • 00:25:40
    dangerous to people so that's why we
  • 00:25:43
    only have uh we we use 120 volts RMS in
  • 00:25:46
    our house because it can kill you but
  • 00:25:48
    it's not going to kill you instantly
  • 00:25:51
    like a um a th000 volts wood or
  • 00:25:56
    higher okay and
  • 00:25:58
    um but the system components need to be
  • 00:26:01
    rated for the higher voltage and safety
  • 00:26:03
    is a
  • 00:26:05
    factor if you the safe range is
  • 00:26:07
    considered around 50 volts if you're
  • 00:26:09
    below 50 volts um like 12 volts you you
  • 00:26:13
    won't generally be uh feel a shock if
  • 00:26:17
    you go above 50 volts then that can get
  • 00:26:22
    dangerous if you touch the
  • 00:26:25
    terminals okay so this is an example
  • 00:26:29
    it's it's really to show trades that we
  • 00:26:32
    can reduce costs significantly we can
  • 00:26:35
    reduce um power loss significantly we
  • 00:26:39
    can reduce weight if this were wiring in
  • 00:26:41
    an airplane uh significantly just by
  • 00:26:45
    considering how we
  • 00:26:47
    configure the components of the
  • 00:26:50
    system here in this case for higher
  • 00:26:51
    voltage if you had more solar panels oh
  • 00:26:55
    let's put them all in series the problem
  • 00:26:56
    is once you exceed 100 volts
  • 00:26:59
    you would destroy the solar charge
  • 00:27:01
    controller um so you could do this you
  • 00:27:04
    can do a combination of series and
  • 00:27:06
    parallel right you could do uh an array
  • 00:27:09
    of four and then multiple arrays of four
  • 00:27:11
    so they're all 72 volts and then connect
  • 00:27:13
    them
  • 00:27:15
    together and uh there are different
  • 00:27:17
    considerations when you have solar
  • 00:27:19
    panels in parallel if they fail open
  • 00:27:23
    then you lose let's say one panel fails
  • 00:27:25
    you lose 25% of your power availability
  • 00:27:29
    um but the system keeps operating here
  • 00:27:31
    if you lose one of these panels and they
  • 00:27:33
    they you know gets hit by hailstones and
  • 00:27:35
    one of them fails as an open circuit
  • 00:27:38
    your whole system is down so this is
  • 00:27:40
    more power efficient but can be more
  • 00:27:45
    vulnerable okay so lots of Trades to
  • 00:27:47
    consider
  • 00:27:57
    here all right so uh that was all about
  • 00:28:00
    Oh's law that was the review of Oh's law
  • 00:28:02
    and I wanted to show some practical
  • 00:28:04
    applications where something as simple
  • 00:28:06
    as Oh's law shows up with some pretty
  • 00:28:08
    significant
  • 00:28:10
    consequences so let's go to a review of
  • 00:28:13
    reactive components we're going to talk
  • 00:28:16
    about
  • 00:28:17
    capacitors and
  • 00:28:21
    inductors so you probably recall that if
  • 00:28:24
    you have a couple conducting plates sep
  • 00:28:26
    separated by a dialectric or or an
  • 00:28:28
    insulator dialectric is an insulator um
  • 00:28:32
    you have a
  • 00:28:33
    capacitor here's the schematic symbol
  • 00:28:36
    for a capacitor there's the voltage and
  • 00:28:38
    the current for that
  • 00:28:40
    capacitor right and in the time domain
  • 00:28:44
    the relationship between voltage and
  • 00:28:46
    current is I is equal to C
  • 00:28:50
    dvdt right so capacitance in farads
  • 00:28:54
    times the derivative the time derivative
  • 00:28:56
    derivative of voltage is is the
  • 00:28:59
    current okay so current is zero when V
  • 00:29:03
    is DC you take the derivative
  • 00:29:05
    of a constant a DC value and you get
  • 00:29:09
    zero current and current only flows when
  • 00:29:12
    V of T is is time varying okay so
  • 00:29:16
    current doesn't actually flow through
  • 00:29:19
    the capacitor from the outside world it
  • 00:29:21
    looks like that it looks like currents
  • 00:29:22
    going back and forth through the
  • 00:29:23
    capacitor but really what's happening is
  • 00:29:26
    the capacitor is charging and
  • 00:29:27
    discharging so so charges flowing into
  • 00:29:30
    the capacitor from one
  • 00:29:31
    terminal uh it charges and then if you
  • 00:29:35
    have a an AC current it's alternately
  • 00:29:38
    charging and discharging that capacitor
  • 00:29:40
    so it looks like current's going through
  • 00:29:41
    it but it's really just a charge and
  • 00:29:44
    discharge um
  • 00:29:47
    State using phasers and impedance if you
  • 00:29:49
    have phaser voltage and phasor current
  • 00:29:53
    then we Define not uh that component not
  • 00:29:56
    with capacitance but with an imped
  • 00:29:58
    Z
  • 00:30:00
    subc and so uh the impedance of that
  • 00:30:04
    capacitor is minus J * one over Omega c
  • 00:30:07
    c is the capacitance Omega is the uh
  • 00:30:11
    angular frequency of of a sinusoid
  • 00:30:14
    usually we're working with sinusoids
  • 00:30:17
    here and V equals Iz right looks like
  • 00:30:20
    Oh's
  • 00:30:22
    law and then the impedance of a
  • 00:30:24
    capacitor Falls with increasing
  • 00:30:26
    frequency so we're going to talk about
  • 00:30:27
    that
  • 00:30:28
    capacitors can be used to filter out
  • 00:30:31
    noise from power supplies or sensor
  • 00:30:34
    voltages and uh we do that because of
  • 00:30:36
    this characteristic that the impedance
  • 00:30:38
    Falls with increasing frequency of a
  • 00:30:43
    capacitor okay so here are some example
  • 00:30:46
    capacitors these are ceramic capacitors
  • 00:30:48
    you have probably something that looks
  • 00:30:50
    like this in your kit maybe something
  • 00:30:52
    that looks like that they come in
  • 00:30:54
    surface mount packages and these leaded
  • 00:30:57
    pack packages through whole
  • 00:31:00
    packages uh they're small size they're
  • 00:31:02
    low cost and they're usually small
  • 00:31:07
    capacitance
  • 00:31:09
    values okay if you need larger
  • 00:31:11
    capacitance values you go to
  • 00:31:14
    electrolytic capacitors so here's uh you
  • 00:31:17
    have capacitors in your kit you will
  • 00:31:20
    that look like
  • 00:31:21
    this these capacitors are polarized and
  • 00:31:25
    usually they have higher capacitance
  • 00:31:27
    values
  • 00:31:29
    but they have a large tolerance and and
  • 00:31:32
    and drift of
  • 00:31:33
    capacitance um if you you know for
  • 00:31:36
    example you might have a 100 microfarad
  • 00:31:39
    capacitor and it might have a 10 or 20%
  • 00:31:43
    tolerance and oftentimes when you use
  • 00:31:46
    these capacitors you don't care so much
  • 00:31:48
    about the exact value you just care
  • 00:31:51
    about its order of magnitude so that you
  • 00:31:53
    can get maybe an impedance low enough to
  • 00:31:57
    work in a filter
  • 00:32:00
    notice in lab you're working with this
  • 00:32:02
    capacitor that these are polarized
  • 00:32:05
    you'll see a usually a minus sign next
  • 00:32:07
    to one of the
  • 00:32:08
    leads sometimes I've seen a plus sign
  • 00:32:11
    next to one of the leads but pay
  • 00:32:14
    attention to the polarity because if you
  • 00:32:15
    put these in with the wrong polarity
  • 00:32:18
    after a while you can degrade the
  • 00:32:19
    capacitor it'll stop
  • 00:32:23
    working and in in lab pay attention to
  • 00:32:27
    when you're building a your uh your
  • 00:32:29
    motor driver circuit you'll get to that
  • 00:32:31
    pay attention to
  • 00:32:33
    that polarity of the capacitor and the
  • 00:32:36
    noted polarity on the schematic and the
  • 00:32:38
    circuit
  • 00:32:40
    board Mica capacitors so mic capacitors
  • 00:32:44
    are generally high voltage
  • 00:32:47
    capacitors and uh we we'll use these
  • 00:32:50
    sometimes for radio frequency
  • 00:32:52
    circuits and they're typically smaller
  • 00:32:55
    capacitance values and they can be
  • 00:32:58
    tighter
  • 00:33:00
    tolerance and then these are variable
  • 00:33:02
    capacitors you can see these inner inle
  • 00:33:04
    fins and you turn this knob and it that
  • 00:33:07
    that adjusts the amount uh that those
  • 00:33:12
    fins overlap and so if they're
  • 00:33:14
    completely overlapped you get a high
  • 00:33:15
    capacitance if they're completely not
  • 00:33:17
    overlapped that's a low capacitance so
  • 00:33:19
    you can build a variable
  • 00:33:21
    capacitor that's that's a big capacitor
  • 00:33:25
    or maybe a high voltage tuning circuit
  • 00:33:27
    here's a
  • 00:33:28
    miniature adjustable variable capacitor
  • 00:33:31
    working on the same
  • 00:33:33
    principle in a different package and a
  • 00:33:35
    lot smaller meant for a circuit
  • 00:33:38
    board okay so when you need to tune a
  • 00:33:41
    circuit you would use those types of
  • 00:33:45
    capacitors but When selecting a
  • 00:33:46
    capacitor here's what you need to
  • 00:33:48
    consider you can't just go say I need a
  • 00:33:49
    10 microfarad capacitor um and just grab
  • 00:33:53
    any capacitor typically you have to
  • 00:33:54
    consider not only size will it fit but
  • 00:33:58
    uh um consider the capacitor's value of
  • 00:34:01
    course and its tolerance do you really
  • 00:34:03
    care if it drifts by 10 or 20% note its
  • 00:34:07
    polarization if it's
  • 00:34:09
    electrolytic and also notice its maximum
  • 00:34:11
    voltage
  • 00:34:13
    rating you can get for example the
  • 00:34:16
    capacitor that's in your
  • 00:34:18
    kit in an electrolytic package like this
  • 00:34:22
    and it's I think it's 100 microfarads
  • 00:34:24
    you can find those in you know 6.7 volts
  • 00:34:27
    or or or um you know different voltage
  • 00:34:31
    values I think you have a 50 volt
  • 00:34:33
    capacitor but if you if you put a 6volt
  • 00:34:37
    capacitor in a 12volt circuit eventually
  • 00:34:39
    you're going to have problems so you got
  • 00:34:40
    to pay attention to more than
  • 00:34:42
    just the capacitance value of a
  • 00:34:47
    capacitor
  • 00:34:51
    okay all right so here's a common
  • 00:34:54
    application for a capacitor um
  • 00:34:58
    filtering either for a
  • 00:35:00
    power uh voltage or a signal voltage
  • 00:35:03
    like from a sensor and also blocking a
  • 00:35:06
    DC voltage is also
  • 00:35:09
    common so let's suppose you have let's
  • 00:35:12
    suppose you have a source DC Source
  • 00:35:15
    here's the thant equivalent we'll talk
  • 00:35:16
    about that of a DC source and then you
  • 00:35:18
    have a DC
  • 00:35:20
    load and you put a wire between these
  • 00:35:22
    could be test leads or jumper wires or
  • 00:35:25
    circuit board traces the copper traces
  • 00:35:27
    on a circuit board could be a breadboard
  • 00:35:29
    connection could be wires across a you
  • 00:35:31
    know some kind of um
  • 00:35:35
    vehicle
  • 00:35:36
    and that wire as we talked about is not
  • 00:35:40
    resistance free it has some resistance
  • 00:35:42
    and it also has some
  • 00:35:44
    inductance and what you've created there
  • 00:35:47
    is basically an antenna you've created a
  • 00:35:50
    way for electromagnetic fields to cause
  • 00:35:54
    a voltage on that wire right we call
  • 00:35:57
    that noise external
  • 00:35:59
    Noise Okay so you get this noise voltage
  • 00:36:02
    across that
  • 00:36:04
    wire and uh
  • 00:36:07
    noise on power supply
  • 00:36:10
    voltages at loads like let's suppose
  • 00:36:12
    this load is a signal amplifier you know
  • 00:36:16
    you're you have a a sensor that needs an
  • 00:36:19
    amplifier time 10 amplifier maybe it's
  • 00:36:21
    an opamp and if you remember from if you
  • 00:36:24
    took my class and you built the op amp
  • 00:36:27
    circuit it's you put decoupling
  • 00:36:29
    capacitors at the ve and
  • 00:36:32
    VCC uh nodes on your board on your
  • 00:36:37
    breadboard but if you if you have a
  • 00:36:39
    noisy DC voltage that can cause uh noisy
  • 00:36:42
    signals out of let's say an amplifier
  • 00:36:45
    you can have noisy sensor signals noisy
  • 00:36:47
    audio
  • 00:36:51
    Etc noise on digital lines like if you
  • 00:36:53
    have some digital chip and you don't
  • 00:36:55
    have a clean power supply signal like
  • 00:36:57
    can cause errors in the values of the of
  • 00:36:59
    the digital signal so this is an analog
  • 00:37:02
    and a digital problem
  • 00:37:05
    problem and what we do is we use
  • 00:37:07
    capacitors and when we use them in this
  • 00:37:09
    way we'll call them decoupling
  • 00:37:11
    capacitors it decouples the noise from
  • 00:37:14
    the from the uh
  • 00:37:17
    circuit so we use these decoupling
  • 00:37:19
    capacitors to reduce noise from the
  • 00:37:22
    external environment and it does that by
  • 00:37:25
    providing a low impedance path to
  • 00:37:28
    ground so this plot here shows the
  • 00:37:31
    magnitude of the
  • 00:37:32
    impedance right of a capacitor and
  • 00:37:35
    here's the frequency in
  • 00:37:37
    hertz so if you have a 100 100
  • 00:37:40
    microfarad capacitor at uh let's see 10
  • 00:37:43
    Herz you have just over 100
  • 00:37:46
    ohms
  • 00:37:48
    impedance
  • 00:37:50
    magnitude
  • 00:37:52
    at let's see that was at 10 Hertz at a
  • 00:37:55
    at 100 Hertz you have just over 10 ohms
  • 00:37:59
    at a th Hertz you have just
  • 00:38:02
    over that's not yeah one ohm trying to
  • 00:38:06
    read this plot
  • 00:38:07
    here okay so you can see the magnitude
  • 00:38:10
    of the impedance falling the magnitude
  • 00:38:12
    of the reactants
  • 00:38:14
    falling as frequency increases and so
  • 00:38:17
    what you're going to use that you're
  • 00:38:18
    going to take that that property that
  • 00:38:21
    characteristic and essentially you're
  • 00:38:23
    creating this low impedance path to
  • 00:38:25
    ground it's like you're shorting from
  • 00:38:27
    this node above the load down to ground
  • 00:38:30
    and that low impedance path uh causes
  • 00:38:33
    the noise voltage to be a lot lower
  • 00:38:36
    across this DC
  • 00:38:38
    load so when you hear decoupling
  • 00:38:40
    capacitors and you see that in lab
  • 00:38:42
    that's what this
  • 00:38:45
    is capacitors can also supply energy
  • 00:38:48
    during transient loading events so you
  • 00:38:51
    know you have a motor that you're
  • 00:38:52
    turning on and off um or a transmitter
  • 00:38:55
    you're turning on and off and that's
  • 00:38:56
    what this DC load might be well because
  • 00:38:59
    of this resistance right here and this
  • 00:39:01
    inductance if you get a rapid change in
  • 00:39:05
    the load like something turns on on the
  • 00:39:07
    right here then you're going to get um
  • 00:39:10
    res a voltage drop across the resistance
  • 00:39:12
    and the inductance as as the current's
  • 00:39:15
    trying to change and so what can happen
  • 00:39:17
    is if you have this capacitance close
  • 00:39:19
    enough to the DC load that capacitors
  • 00:39:21
    charged energy can supply the load with
  • 00:39:25
    energy with power um
  • 00:39:27
    while that transient event is occurring
  • 00:39:30
    so this will this will reduce the
  • 00:39:32
    fluctuation of voltage at the DC load if
  • 00:39:35
    you have a a capacitor at that load so
  • 00:39:39
    reducing noise and supplying energy
  • 00:39:41
    during transient loading
  • 00:39:47
    events and capacitors are also often
  • 00:39:50
    used to pass AC signals and block DC
  • 00:39:54
    signals so if you have to couple an
  • 00:39:56
    audio signal into an amplifier and you
  • 00:39:58
    want to isolate DC on either side of the
  • 00:40:01
    capacitor you can do that you just have
  • 00:40:04
    to pick a big enough large enough
  • 00:40:06
    capacitor so that it its impedance is
  • 00:40:09
    low enough uh compared to what you
  • 00:40:12
    need okay and so it's it's good practice
  • 00:40:16
    to use one or more decoupling capacitors
  • 00:40:18
    near the power pins of
  • 00:40:21
    ic's so that's what we did in the
  • 00:40:23
    circuits lab if you took my circuits
  • 00:40:26
    class we put capacitors right next to
  • 00:40:29
    the the opamp on its power
  • 00:40:31
    pins and you'll see this you'll see this
  • 00:40:34
    commonly on circuit boards and in other
  • 00:40:37
    circuits you'll see capacitors where
  • 00:40:39
    they appear they don't really do
  • 00:40:40
    anything because they're sitting there
  • 00:40:41
    on a DC line and capacitors should be
  • 00:40:45
    open for DC fact is there's more than DC
  • 00:40:49
    on that wire there's AC
  • 00:40:51
    being conducted in from external sources
  • 00:40:54
    or uh received from external
  • 00:40:57
    electromagnetic
  • 00:41:02
    sources okay so in practice let's take a
  • 00:41:05
    look at some decoupling capacitors here
  • 00:41:08
    is a schematic of your lab project that
  • 00:41:10
    you will start this Friday right
  • 00:41:13
    microcontroller board a bunch of sensors
  • 00:41:16
    couple sensors DC to DC converter
  • 00:41:18
    battery
  • 00:41:20
    motor so what you'll see are all these
  • 00:41:23
    capacitors and they don't look like
  • 00:41:24
    they're doing anything they're on either
  • 00:41:26
    d C
  • 00:41:29
    nodes lines or they're uh connected to
  • 00:41:32
    slowly varying like temperature it's
  • 00:41:35
    slowly varying
  • 00:41:36
    line uh so you see these these
  • 00:41:39
    capacitors here the intent with all
  • 00:41:41
    those capacitors is to reduce noise and
  • 00:41:46
    so you have this motor here Motors are
  • 00:41:48
    are noisy devices especially brushed
  • 00:41:50
    motors brushed motors if you remember
  • 00:41:52
    from intro to circuits they have a
  • 00:41:55
    commutator and a piece of metal a brush
  • 00:41:57
    that rubs against it and and the current
  • 00:41:59
    starting and stopping that's usually
  • 00:42:02
    emitting uh uh some kind of sign some
  • 00:42:06
    kind of em field causing noise
  • 00:42:08
    throughout the rest of your circuit and
  • 00:42:10
    also the start and the stop of the
  • 00:42:12
    current and the sparking going on inside
  • 00:42:13
    that motor causes conducted noise too
  • 00:42:16
    into power supplies and and nearby
  • 00:42:19
    circuits so these
  • 00:42:22
    capacitors uh
  • 00:42:24
    reduce that noise so you try to take
  • 00:42:27
    them all out of your project and it
  • 00:42:29
    might work sometimes it might not trust
  • 00:42:32
    me on that because I I designed this I I
  • 00:42:35
    put it together and and sometimes things
  • 00:42:38
    weren't working ahuh you measure the
  • 00:42:41
    voltages with an oscilloscope and you
  • 00:42:42
    see oh there's there's an ac voltage
  • 00:42:46
    coupled into this line and the IR sensor
  • 00:42:48
    doesn't like that or the microcontroller
  • 00:42:50
    is triggering on a on a signal I didn't
  • 00:42:53
    expect to be there
  • 00:42:59
    okay and you'll see on so this is your
  • 00:43:02
    project on the left this is an Arduino
  • 00:43:04
    Uno schematic on the
  • 00:43:06
    right and so you can see the
  • 00:43:08
    microcontroller and some supporting
  • 00:43:10
    integrated circuits here and I've
  • 00:43:14
    circled many maybe all of the decoupling
  • 00:43:18
    capacitors right here's one on the upper
  • 00:43:19
    left between the 5volt power supply and
  • 00:43:21
    ground you have a 0.1 microfarad 100
  • 00:43:24
    nanofarad capacitor 0.1 microfarads is
  • 00:43:27
    very common
  • 00:43:29
    for relatively low speeed devices um
  • 00:43:34
    like this microcontroller like your
  • 00:43:35
    project does a good job at filtering out
  • 00:43:39
    it's it's the right impedance for the
  • 00:43:40
    frequencies that you would expect
  • 00:43:41
    showing up on these DC lines or slowly
  • 00:43:45
    varying sensor
  • 00:43:47
    voltages so you can see them all here
  • 00:43:49
    here's a 3.3 volt decoupling capacitor
  • 00:43:52
    uh here's another one right next to that
  • 00:43:54
    chip you have another decoupling
  • 00:43:56
    capacitor here's another one
  • 00:43:57
    right next to that chip and usually
  • 00:43:59
    physically you put those very
  • 00:44:01
    close to the uh the chip you're trying
  • 00:44:04
    to protect here's a what is that that's
  • 00:44:06
    an analog reference for an analog to
  • 00:44:08
    digital converter it's also it also has
  • 00:44:11
    a decoupling capacitor right there so
  • 00:44:15
    they become they become
  • 00:44:22
    important okay so the main purpose of
  • 00:44:26
    the takeaway here of of these capacitors
  • 00:44:28
    is to remove unwanted AC noise from the
  • 00:44:31
    DC voltages you want DC or slowly
  • 00:44:33
    varying AC VAR slowly varying
  • 00:44:37
    voltages and uh these capacitors do that
  • 00:44:40
    and they supply energy during transient
  • 00:44:42
    loading
  • 00:44:47
    events
  • 00:44:51
    right okay so here's an example just
  • 00:44:54
    want to finish this off with something
  • 00:44:57
    something practical
  • 00:45:00
    here if I have a sensor with a 10 kilohm
  • 00:45:03
    out output
  • 00:45:05
    impedance and I have a Data Logger with
  • 00:45:07
    a 10kohm input impedance right and I
  • 00:45:10
    just connect them together and I did
  • 00:45:12
    this actually did this on a bench I had
  • 00:45:13
    a um a a 10K output impedance on a
  • 00:45:17
    voltage and uh a uh analog to digital
  • 00:45:22
    converter with a 10K input
  • 00:45:24
    impedance and so this is the oscope
  • 00:45:28
    Trace with no
  • 00:45:30
    capacitor okay so you can see let's see
  • 00:45:33
    what's the timing here 500 micros
  • 00:45:35
    seconds per division 500 molts per
  • 00:45:38
    Division and we have a 3vt DC voltage
  • 00:45:42
    except look at all that noise on there
  • 00:45:44
    that noise is about 77 molts
  • 00:45:47
    RMS I've got a measurement somewhere on
  • 00:45:52
    here okay but what happens if we add a
  • 00:45:55
    capacitor just a 0.1 microf capacitor
  • 00:45:57
    close to that Data Logger this happens
  • 00:46:01
    you get this
  • 00:46:03
    so uh same circuit just add that
  • 00:46:06
    capacitor you still have a three point
  • 00:46:08
    or a 3vt
  • 00:46:09
    DC
  • 00:46:11
    voltage but you have
  • 00:46:14
    um much
  • 00:46:16
    smaller RMS noise so six
  • 00:46:21
    molts okay so that's huge that's a big
  • 00:46:24
    difference so adding just that 1.1
  • 00:46:26
    microfarad capacitor reduced the noise
  • 00:46:29
    voltage by 92% reduced the noise Power
  • 00:46:31
    by
  • 00:46:33
    99% and you know do you need it do you
  • 00:46:36
    know if you have a device that is
  • 00:46:37
    intended to have DC then having more
  • 00:46:41
    than a few molts of noise can be
  • 00:46:46
    bad especially on on circuit
  • 00:46:53
    boards all right so that's an example
  • 00:46:55
    there's a kind of a you know capacitor
  • 00:46:57
    review we we talked theory in the C
  • 00:47:01
    circuits class here are
  • 00:47:03
    some less theoretical more practical
  • 00:47:06
    applications of capacitors that show up
  • 00:47:13
    everywhere right so let's let's review
  • 00:47:15
    inductors
  • 00:47:16
    inductors um you have a coil of wire the
  • 00:47:19
    coil of wire creates a magnetic field if
  • 00:47:21
    you try to change the current through
  • 00:47:23
    that coil of wire you get a Time varying
  • 00:47:25
    magnetic field because of the time
  • 00:47:27
    varying current a Time varying magnetic
  • 00:47:30
    field through a coil of wire induces a
  • 00:47:33
    voltage okay that's Faraday's law so
  • 00:47:37
    here's the schematic
  • 00:47:38
    symbol voltage and current in the time
  • 00:47:41
    domain
  • 00:47:43
    shown uh here's the relationship between
  • 00:47:46
    voltage and current so right if you try
  • 00:47:50
    to change the
  • 00:47:52
    current if you try to change that
  • 00:47:55
    current that's derivative is going to be
  • 00:47:58
    non zero so you're going to induce a
  • 00:48:01
    voltage and L is inductance which is uh
  • 00:48:05
    calculated from or determined by the
  • 00:48:08
    number size of the coil the number of
  • 00:48:10
    turns the material that's used as a core
  • 00:48:13
    spacing of the
  • 00:48:14
    turns um it's for a given
  • 00:48:19
    inductor okay so the voltage is zero
  • 00:48:22
    when I of T is is is DC
  • 00:48:27
    right because if I have a DC
  • 00:48:29
    current then the derivative is zero so I
  • 00:48:32
    get no voltage and the voltage is non
  • 00:48:34
    zero only when I of T is
  • 00:48:38
    varying
  • 00:48:40
    okay and in uh using phaser notation
  • 00:48:46
    here's voltage current and impedance of
  • 00:48:49
    that inductor where impedance is J Omega
  • 00:48:53
    L and then V equals Iz looks like Ohm's
  • 00:48:56
    law but with complex
  • 00:48:59
    numbers and you can see that imped the
  • 00:49:02
    impedance of an inductor increases with
  • 00:49:04
    increasing frequency so you can actually
  • 00:49:06
    use inductors to block AC at higher
  • 00:49:11
    frequencies because the impedance goes
  • 00:49:16
    up okay so some examples here here are
  • 00:49:20
    some cylindrical or or solenoid
  • 00:49:23
    inductors here's an air core inductor
  • 00:49:25
    here's an um probably a ferite core
  • 00:49:28
    inductor there just a coil of wire
  • 00:49:31
    they're small and they're low cost
  • 00:49:33
    here's a toid if you need um High
  • 00:49:36
    inductance then you might use a toroid
  • 00:49:39
    and they can get they could be they
  • 00:49:41
    could be tiny you know fractions of an
  • 00:49:44
    inch up to inches in diameter and that
  • 00:49:48
    contains the magnetic field and makes
  • 00:49:50
    the uh the inductance higher for a given
  • 00:49:54
    number of turns there's surface mount
  • 00:49:56
    inductors coil of wire around what's
  • 00:49:58
    called a bobin here here's some enclosed
  • 00:50:01
    encapsulated
  • 00:50:03
    inductors okay and they're meant to
  • 00:50:05
    mount on printed circuit boards here's
  • 00:50:07
    some axial through hole inductors they
  • 00:50:09
    look like this you can read that color
  • 00:50:11
    code figure out their values and they
  • 00:50:14
    mount on through hole
  • 00:50:17
    pcbs and just like capacitors when you
  • 00:50:21
    select an inductor you've got to select
  • 00:50:23
    not only the inductance value but also
  • 00:50:25
    the tolerance
  • 00:50:27
    the frequency and the loss
  • 00:50:28
    characteristics of that
  • 00:50:30
    inductor and also from a mechanical
  • 00:50:33
    perspective size and weight you're
  • 00:50:35
    probably not going to take a big to
  • 00:50:38
    toroidal um inductor on a on a big toid
  • 00:50:42
    core and fit it into a cell phone right
  • 00:50:43
    so if you're designing electronics that
  • 00:50:45
    have to fit into a small package then
  • 00:50:47
    you've got to consider when you see an
  • 00:50:50
    inductance of maybe milen some big
  • 00:50:53
    inductance then uh and how much power
  • 00:50:55
    does it have to handle
  • 00:50:59
    you you you might have to look at
  • 00:51:01
    Alternatives because of mechanical
  • 00:51:04
    constraints
  • 00:51:06
    so all right so I've gone uh a minute
  • 00:51:10
    over on time here and so uh let's end
  • 00:51:15
    class right
  • 00:51:16
    now and in closing please see canvas for
  • 00:51:21
    upcoming assignments you have lab
  • 00:51:23
    homework one do and then lab one will
  • 00:51:27
    uh be held this week so I will see you
  • 00:51:29
    in lab on Friday um also see the itll
  • 00:51:32
    workshops if there's anything that we
  • 00:51:34
    talked about like soldering or um
  • 00:51:38
    microcontrollers that we talked about
  • 00:51:40
    our topics of this class and you want a
  • 00:51:41
    refresher be sure to sign up for one of
  • 00:51:44
    those workshops as maybe a refresher or
  • 00:51:47
    an
  • 00:51:48
    introduction uh what else let's
  • 00:51:50
    see and uh just expect to come into lab
  • 00:51:53
    this Friday form your lab group and
  • 00:51:55
    we'll get started started there so I
  • 00:51:58
    will start office hours right after
  • 00:52:01
    class uh so if you'd like to chat just
  • 00:52:03
    just stick around if not I'll see you
  • 00:52:06
    next time have a great night
标签
  • assignatures
  • laboratori
  • projecte
  • teoria del circuit
  • resistència
  • components reactius
  • condensadors
  • inductors
  • eficiència del circuit