Dasar Elektronika (2) : Komponen Aktif dan Pasif

Komponen elektronika aktif memerlukan sumber arus dan tegangan tersendiri. Sumber arus dan tegangan dibutuhkan oleh komponen aktif dengan besar tertentu agar dapat beroperasi sesuai dengan yang diinginkan. Komponen aktif juga dapat menghasilkan energi atau tenaga listrik dari dirinya sendiri yang diberikan ke komponen pasif dalam sebuah rangkaian. Oleh karena itu, merangkai komponen aktif dalam sebuah rangkaian elektronika tidak dapat dilakukan secara sembarangan. 

Komponen aktif elektronika dapat berupa komponen elektronika digital maupun komponen elektronika analog. Transistor dan dioda merupakan komponen aktif analog yang sering digunakan pada rangkaian robot. Komponen digitalnya biasanya berupa IC (integrated circuit).

Komponen pasif elektronika semuanya termasuk ke dalam jenis komponen analog. Pemasangan komponen pasif pada rangkaian elektronika tidak memerlukan sumber arus dan tegangan dengan aturan tertentu. Komponen ini juga tidak dapat menghasilkan energi atau tenaga listrik. Komponen pasif mengambil energi listrik dari sumber rangkaian. Beberapa contoh komponen pasif yang banyak digunakan pada sebuah rangkaian robot yaitu resistor, kapasitor, trafo, relay, dan saklar.

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Dasar Elektronika (1) : Komponen analog dan digital

Elektronika sebagai salah satu cabang dari robotika dapat didefinisikan sebagai ilmu pengetahuan yang mempelajari arus lemah untuk menjalankan peralatan listrik dengan cara melakukan pengontrolan aliran elektron (partikel yang bermuatan listrik). Elektronika adalah cabang dari ilmu fisika, sedangkan perancangan dan pembuatan rangkaian elektronika adalah bagian dari teknik elektro, teknik komputer, dan teknik elektronika dan instrumentasi.Berdasarkan sistem kerja dan karakteristiknya elektronika dibagi dua bagian besar yaitu elektronika analog dan elektronika digital.

Elektronika digital hanya mengenal dua kondisi yaitu kondisi "nol" dan kondisi "satu". Namun, kondisi "nol" tidak selalu bernilai 0 volt. Istilah lain dari “kondisi” dalam elektronika digital adalah “logic” (baca :  logika).Logic 0 juga dikenal dengan keadaan “Low (L)” atau False (F)” dan logic 1 adalah  keadaan “High (H)” atau “True (T)”. Dengan demikian, perbedaan antara elektronika analog dan elektroika digital terletak pada input yang diolah dan output yang dihasilkan, linearitas nilai input dan output, bentuk gelombang, dan flexibilitas tegangan sumber sehingga komponen elektronika yang digunakan pun berbeda. Rangkaian elektronika yang digunakan dalam sistem kendali sebuah robot pada umumnya merupakan rangkaian elektronika yang tersusun dari gabungan komponen-komponen analog dan digital.

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Robot cerdas karena apa ?

Pernah mendengar istilah robot cerdas? Apakah berbeda antara robot (biasa) dengan robot cerdas ? Kalau ada robot (yang) cerdas, lantas robot lain (yang tidak cerdas) disebut robot apa ya?

Fungsi robot sebagai sebuah alat yang dapat membantu pekerjaan manusia dapat dibedakan berdasarkan kendalinya. Ada yang harus di bawah kendali manusia. Ada juga yang dapat menjalankan fungsinya secara otomatis tanpa harus dikendalikan oleh manusia. Jenis yang terakhir inilah yang dinamakan robot cerdas.

Robot cerdas dilengkapi sebuah sistem kendali sehingga robot dapat menjalankan fungsinya tanpa dikendalikan manusia. Sistem kendali seperti ini biasa disebut dengan sistem cerdas atau kecerdasan buatan (artificial intellegent). Dewasa ini, sistem cerdas sebuah robot berupa program yang ditanamkan pada sebuah chip mikrokontroler/ mikroprosesor.

Robot yang menggunakan mikrokontroler/ mikroprosesor dikenal dengan sebutan robot mikro. Namun demikian, robot cerdas juga bisa berupa robot analog (tanpa mikrokontroler atau mikroprosesor). Sistem kendalinya bukan berupa program melainkan berupa rangkaian elektronika yang dirancang agar robot dapat 'bertugas otomatis'.

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Apa bedanya robot dan robotika?

Bicara soal robot, pasti kita juga sering mendengar istilah robotika. Pertanyaannya, apakah robotika dan robot itu sama? Bagaimana keterkaitan antara robot dan robotika?

Setelah mengenal robot, kita tahu bahwa robot adalah benda atau barang, sedangkan robotika diartikan sebagai adalah satu cabang teknologi yang berhubungan dengan desain, konstruksi, operasi, disposisi struktural, pembuatan, dan aplikasi dari robot.

Robotika adalah cabang ilmu yang mempelajari semua hal terkait dengan teknologi robot. Sebuah robot, telah kita ketahui, tersusun dari tiga bagian : mekanik, kendali dan penggerak. Bidang mekanik sebuah robot dipelajari dalam pembahasan mekanika. Unit kendali robot biasanya berupa rangkaian-rangkaian elektronik baik itu yang dapat diprogram maupun tidak. Sedangkan unit penggerak robot biasanya berupa motor.

Cabang ilmu robotika meliputi pengetahuan bidang elektronika, mesin, mekanika, dan pemrograman (kecerdasan buatan). Oleh karena itu, jika kita berminat menjadi seorang ahli di bidang robotika, kita tidak perlu menjadi ahli di semua bidang (elektronika, mekanika, dan pemrograman untuk kontrol). Kita harus memahami dasar dan konsep secara umum, tetapi kita bisa mengambil peran menjadi ahli dari salah satu bidang pengetahuan tersebut. Think global but become specialist. Apakah kita lebih suka dan mampu di bidang elektronika, mekanika, atau pemrogramannya.

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Berbagai Jenis Robot

Sebuah robot dibangun dari tiga bagian dasar (Eugene, 1976):

1. Struktur mekanis, yaitu sambungan-sambungan mekanis (link) dan pasangan-pasangan (joint) yang memungkinkan untuk membuat berbagai variasi gerakan.

2. Sistem kendali, dapat berupa kendali tetap (fixed) ataupun servo. Sistem kendali tetap yaitu suatu kendali robot yang pengaturan gerakannya mengikuti lintasan (path), sedangkan kendali servo yaitu suatu kendali robot yang pengaturan gerakannya dilakukan secara point to point (PTP) atau titik pertitik.

3. Unit penggerak (actuator), seperti hidrolik, fenumatik, elektrik ataupun kombinasi dari ketiganya, dengan atau tanpa sistim transmisi. Torsi (force) dan kecepatan yang tersedia pada suatu aktuator diperlukan untuk mengendalikan posisi dan kecepatan. Transmisi diperlukan untuk menggandakan torsi. Seperti diketahui menambah torsi dapat menurunkan kecepatan, dan meningkatkan inersia efektif pada sambungan. Untuk mengurangi berat suatu sistem robot maka aktuator tidak ditempatkan pada bagian yang digerakkan, tetapi pada sambungan yang sebelumnya. Ada beberapa jenis transmisi yang banyak dipakai, antara lain Belt, Cable, Chain dan roda gigi.

Seiring dengan berkembangnya teknologi, khususnya teknologi elektronik, peran robot menjadi semakin penting tidak saja dibidang sains, tapi juga di berbagai bidang lainnya, seperti di bidang kedokteran, pertanian, bahkan militer.  Ada jenis robot sederhana yang dirancang untuk melakukan kegiatan yang sederhana, mudah dan berulang-ulang, ataupun robot yang diciptakan khusus untuk melakukan sesuatu yang rumit, sehingga dapat berperilaku sangat kompleks dan secara otomatis dapat mengontrol dirinya sendiri sampai batas tertentu.

Secara sadar atau tidak, saat ini robot telah masuk dalam kehidupan manusia sehari-hari dalam berbagai bentuk dan jenis. Namun demikian, robot secara umum dapat dikelompokkan berdasarkan jenis konstruksinya :
(http://id.wikipedia.org/wiki/Robot,2010)
1. Robot Mobile
2. Robot Manipulator
3. Robot Humanoid
4. Flying Robot
5. Robot Berkaki
6. Robot jaringan
7. Robot Animalia

Berikut akan dijelaskan satu per satu secara ringkas.

1.Robot Mobile
Robot jenis ini merupakan robot yang paling banyak dipelajari dan dibuat dalam tahap belajar membuat robot pemula. Tinggat kesulitan untuk membuat robot ini relatif masih rendah. Untuk dapat membuat robot ini harus mengerti tentang sensor-sensor elektronik dan mikrokontroler. Robot ini biasanya menggunakan beberapa roda untuk memudahkan pergerakannya. Robot ini bergerak mengikuti pembacaan sensor-sensor yang telah ditetapkan pada sistem robot ini. Beberapa contoh dari jenis robot mobile yaitu, robot pengikut garis, robot pengikut cahaya, robot avoider beroda.

2. Robot Manipulator
Robot ini banyak dipakai oleh perusaan industri elektronik ataupun transportasi. Robot jenis ini juga dikenal dengan sebutan lengan robot karena berbentuk seperti sebuah lengan atau tangan. Robot jenis ini mempunyai peran pekerjaan masing-masing. Contohnya robot untuk menutup kaleng, mengecat, memasang baut yang berukuran kecil maupun besar, menyatukan body mobil dan masih banyak yang lainnya.

3. Robot Humanoid
Human artinya manusia. Jenis robot yang satu ini lebih mirip ke manusia dari segi bentuk. Robot humanoid mempunyai 2 tangan, 2 kaki dan satu kepala. Adapun dari segi fungsinya, ada robot jenis ini yang dapat kita ajak berbicara. Robot jenis ini selalu berkembang dan semakin canggih.

4. Flying Robot
Robot ini ditempatkan dilangit/mengudara. Biasanya robot jenis ini seringkali digunakan untuk mengambil gambar dari atas karena tidak memungkin jika manusia terbang dan mengambil gambar dari atas kecualing dengan naik pesawat. Robot jenis ini saat ini sedang populer dengan istilah droid. Contohnya adalah quadcopter yang mulai digunakan dalam liputan media.

5. Robot Berkaki
Bentuk robot ini sesuai dengan namanya yaitu robot berkaki, berarti robot ini mempunyai kaki. Biasanya robot ini banyak masuk kedalam jenis robot bentuk hewan. Contohnya robot anjing yang mempunyai 4 kaki, Laba-laba dengan 6 kaki atau lebih.

6. Robot Jaringan
Apakah robot jenis jaringan itu? Robot jaringan merupakan jenis robot sebagai aplikasi dari perkembangan  bidang jaringan komputer.  Robot jaringan adalah pendekatan baru untuk melakukan kontrol robot menggunakan jaringan internet dengan protokol TCP/IP. Dengan koneksi jaringan, proses kontrol dan monitoring, termasuk akuisisi data bila ada, seluruhnya dilakukan melalui jaringan komputer/ internet.

7. Robot animalia
Robot ini dibuat menyerupai bentuk dan tingkah laku hewan, robot ini biasanya di pesan oleh pemelihara hewan.

Ada satu kelompok robot lagi yang juga disebutkan pada pembahasan jenis-jenis robot, yaitu Underwater Robot. Robot underwater adalah robot yang digunakan dibawah permukaan air atau didalam air. Untuk robot jenis ini yang berukuran besar biasanya untuk mengambil suatu barang penting yang terdapat didalam air yang mungkin tidak dapat dijangkau oleh manusia. Robot ini juga seringkali digunakan sebagai alat yang memonitoring suata keadaan bawah air.

Itulah berbagai jenis robot yang dikemukakan oleh para ahli. Sekarang, dapatkah kita mengidentifikasi 'robot' yang ada di sekitar kita? Selamat mengeksplorasi !

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Mengenal Robot

Saat mendengar kata 'robot', apa yang seketika muncul dalam benak kita? Kebanyakan orang awam akan membayangkannya seperti yang ada di film-film populer. Film-film sejenis transformer secara tidak langsung berhaail menggiring opini kita tentang robot.

Sebenarnya, robot itu apa sih? Apakah robot selalu berbentuk seperti dalam film? Apakah robot berbentuk seperti manusia? Apakah robot akan membantu manusia atau mengancam manusia? Tidak sedikit yang punya pertanyaan semacam ini kan?

Robot sejatinya adalah perkembangan dari mesin. Mesin secara istilah didefinisikan sebagai alat yang dapat membantu manusia menyelesaikan pekerjaannya. Begitu juga robot, dapat kita definisikan sebagai sebuah alat untuk membantu manusia menyelesaikan pekerjaan. Jika demikian apakah robot sama dengan mesin?

Kata robot diambil dari bahasa Ceko (Chech), yang memiliki arti pekerja (worker). Robot merupakan suatu perangkat mekanik yang mampu menjalankan tugas-tugas fisik, baik di bawah kendali dan pengawasan manusia, ataupun yang dijalankan dengan serangkaian program yang telah didefinisikan terlebih dahulu atau kecerdasan buatan (artificial intelligence).

Ada banyak defenisi yang dikemukakan oleh para ahli mengenai robot. Beberapa ahli robotika berupaya memberikan beberapa defenisi, antara lain
(Gonzalez, 1987) :

a. Robot adalah sebuah manipulator yang dapat di program ulang untuk memindahkan tool, material, atau peralatan tertentu dengan berbagai program pergerakan untuk berbagai tugas dan juga mengendalikan serta mensinkronkan peralatan dengan pekerjaannya, oleh Robot Institute of America.

b. Robot adalah sebuah sistem mekanik yang mempunyai fungsi gerak analog untuk fungsi gerak organisme hidup, atau kombinasi dari banyak fungsi gerak dengan fungsi intelligent, oleh official Japanese.

Setelah menyimak berbagai definisi robot, maka dapat saya simpulkan bahwa yang membedakan robot dengan mesin adalah pergerakannya. Pergerakan robot biasanya berupa perpindahan, meskipun tidak semua bagiannya mengalami perpindahan, seperti pada jenis lengan robot. Sedangkan mesin biasanya hanya diam di tempat, yang bergerak adalah bagian di dalamnya. Contohnya mesin cuci.

Robot biasanya digunakan untuk tugas yang berat, berbahaya, pekerjaan yang berulang dan kotor. Di Indonesia, robot sudah banyak digunakan di bidang industri. Kebanyakan robot industri digunakan dalam bidang produksi. Penggunaan robot lainnya termasuk untuk pembersihan limbah beracun, penjelajahan bawah air dan luar angkasa, pertambangan, pekerjaan “cari dan tolong” (search and rescue). Belakangan ini robot mulai memasuki pasaran konsumen di bidang hiburan, dan alat pembantu rumah tangga, seperti penyedot debu, dan pemotong rumput.

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Current, Voltage, and Power

Voltage is related to potential-energy difference. The voltage drop across any circuit element is directly proportional to the change in energy of a charge as it traverses the circuit element. Specifically, 1 volt = 1 joule/coulomb. The potential energy (with respect to some reference point) is equal to the voltage multiplied by the charge.

Current refers to the motion of charges. The current through a given surface (e.g. the cross-section of a wire) is defined as the net charge passing through that surface per unit time. The unit for current is the ampere: 1 ampere = 1 coulomb/second.

The product of voltage and current has units of joules/second, otherwise known as watts.

If the voltage drop across a circuit element equals the change in potential energy per unit charge, and the current equals the amount of charge moving through the element per unit time, then their product equals the power released within the device!
 
The power dissipated within any device is given by
P = IV (2.11)

For resistive elements (or when an effective resistance can be defined), Eq. 2.11 can be combined with Ohm’s law to give:
P = IV = I 2 R = V 2 /R  (2.12)

Resistors, diodes, transistors, relays, integrated-circuit chips, etc., are rated (in part) by their maximum allowed power. Exceeding these ratings can have  disastrous effects on your circuit, and may even cause a fire! To illustrate this point, our first exercise will deliberately lead to the destruction of a carbon-film resistor.

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Capacitors (Part 2)

Capacitors are the second most commonly used component in electronics. They
can be thought of as tiny rechargeable batteries—capacitors can be charged and
discharged. The amount of charge that a capacitor can hold is measured in Far-
ads or the letter F. However, 1F is too large for capacitors, so microfarads (μF)
and picofarads (pF) are used:



micro = 1/1,000,000 and pico = 1/1,000,000,000,000
So, 100,000pF = 0.1μF = 0.0000001F

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Device Electrical Characteristics

The resistor is a linear device and is characterized by a “straight-line equation”. It dissipates power as heat, its value in ohms can vary as to the tolerance rating (ohms ± % of rated value). The resistor cannot store energy.

An inductor or capacitor is an energy storage device; a capacitor’s current or an inductor’s voltage does not change instantaneously. Initial conditions can apply to both of these devices.

The ideal capacitor has zero conductance or infinite resistance and the ideal inductor has zero resistance or infinite conductance. Ideally, neither device dissipates heat (power). The total power consumed or delivered in an RLC is presented as a complex variable (phasor) with a real (dissipated power by resistors) and imaginary (reactive power ) component.

It should be mentioned that, a capacitor’s conductance (or an inductor’s resistance) only approaches zero and the rated component value (Farads for capacitors or Henries for inductors) may also vary. These variants in addition to EMI and environmental effects would require you to alter your design or analysis somewhat, depending on how critical they are to your design or model.

The Ideal voltage vs. current characteristics for the resistor, inductor and capacitor are shown below in Table 1.

source : PDHengineer.com
Course No E-6002
First Order RLC Circuits: Time Domain
Analysis

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Breadboard

Circuits can be modeled to make sure they work the way you want them to. Circuit modeling can be done either using a computer modeling application, or on a prototype board—also called a breadboard or Vero board—which is a board covered with small sockets into which components can be plugged and connected up.

Figure above shows a breadboard with holes connected in two long rows at the top and bottom, and columns of five linked holes elsewhere. Electronic components and wires can be simply plugged into the board in order to make any required circuit connections. The top and bottom rows act as power supply chan-
nels for the circuit.

Evaluation and Testing

Evaluation and testing is about making sure that the product stays on track with
the design specification. You should plan to evaluate and test your project at a
number of key stages of design and manufacture. These stages are referred to as
critical control points.
The critical control points for evaluation and testing an electronic prod-
uct are:

1. Initial Design Phase: Check that you have used the correct value components, and that the various systems work together. These checks can be done using a computer-simulation package.
   Breadboard Phase: Use the breadboard to check whether the circuit works properly. Test each part of the circuit using a millimeter or logic probe.
2. PCB Layout: Check that the components are in the correct positions and that you have used the optimum track layout. Make sure that the components are located neatly and that joints are well soldered.
3. Manufacturing and Packaging Phase: After manufacture, check that the product conforms to its specification. During packaging, check that the product fits securely in the package, and that any conducting parts are insulated.
4. Finally, the Analysis Phase: Look back over the design and making process. Analyze how well it went, noting any modifications and improvements you would make if you were to do it again. These notes are an important part of your design portfolio.

Taken  from

Appin Knowledges Solution. 2007. Robotics. New Delhi. Infinity Science Press LLC

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Capacitors

A capacitor is a component that stores an electrical charge. It consists of two plates separated by an insulator. The amount of capacitance is measured in Farads but as this is too large a unit for everyday electronics we use smaller units such as microfarads and smaller. Capacitors come in many types including electrolytic, polyster, polypropylene, ceramic, paper and mica.

Measurement and Testing

The best check of a capacitor is to use a meter designed to perform the necessary tests. However, an ohmmeter can identify those in which the dielectric has deteriorated (especially in paper and electrolytic capacitors). As the dielectric breaks down, the insulating qualities decrease to a point where the resistance between the plates drops to a relatively low level. After ensuring that the capacitor is fully discharged, place an ohmmeter across the capacitor, as shown in figure. In a polarized capacitor, the polarities of the meter should match those of the capacitor. A low-resistance reading (zero ohms to a few hundred ohms) normally indicates a defective capacitor.

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Resistor Combination

Resistors can be connected such parallel or series.

Resistors are in series if they are connected in tandem and carry exactly the same current. Resistors are arranged in a chain, so the current has only one path to take. The current is the same through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors.

Resistors are in parallel if they are connected in the same nodes and have exactly the same voltage across their terminals. Resistors are arranged with their heads connected together, and their tails connected together. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The voltage across each resistor in parallel is the same. The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total.

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TYPES OF RESISTORS

Resistors are made in many forms, but all belong in either of two groups: fixed or variable. The relative sizes of all fixed and variable resistors change with the wattage (power) rating, increasing in size for increased wattage ratings in order to withstand the higher currents and dissipation losses.

• Fixed Resistors

Resistors of this type are readily available in values ranging from 2.7 ⍀ to 22 M⍀. For use with printed circuit boards, fixed resistor networks in a variety of configurations are available in miniature packages.

• Variable Resistors

Variable resistors, as the name implies, have a terminal resistance that can be varied by turning a dial, knob, screw, or whatever seems appropriate for the application. They can have two or three terminals, but most have three terminals. If the two- or three-terminal device is used as a variable resistor, it is usually referred to as a rheostat. If the three- terminal device is used for controlling potential levels, it is then commonly called a potentiometer. Even though a three-terminal device can be used as a rheostat or potentiometer (depending on how it is connected), it is typically called a potentiometer when listed in trade magazines or requested for a particular application .

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Measuring Voltage

Voltage is always referenced to something, usually a local ground. To measure a voltage, you will first connect the ‘common’ jack of the meter to the circuit common (i.e., breadboard ground). Next you will connect the meter’s ‘voltage’ jack to the point of interest. The meter will then tell you the voltage with respect to ground at this one point.

When connecting things, it’s always a good idea to use color coding to help keep track of which lead is connected to what. Use a black banana plug lead to connect the ‘common’ input of the meter to the ‘ground’ jack. Use a red banana-plug lead with the ‘V’ input of the meter.
 

(a) An arbitrary circuit diagram is shown as an illustration of how to use a voltmeter. Note that the meter measures the voltage drop across both the resistor and capacitor (which have identical voltage drops since they are connected in parallel).
(b) A drawing of the same circuit showing how the leads for a DMM should be connected when measuring voltage. Notice how the meter is connected in parallel with the resistor.

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Kirchhoff’s Law

In 1845, German physicist Gustav Kirchhoff first described two laws that became central to electrical engineering. The laws were generalized from the work of Georg Ohm. The laws can also be derived from Maxwell’s equations, but were developed prior to Maxwell’s work. 

• Kirchhoff’s Current Law (KCL):

        The algebraic sum of  the currents entering any node is zero  

        This law is also called Node analysis

       This Law is used in circuit analysis to define relationships between currents flowing in branches of the circuit. For example, in figure above the currents flowing in the four branches connected to the node have been defined as I1, I2, I3, I4 and Kirchhoff’s Current Law allows us to write down an equation relating these currents. Looking closely at figure above, we see that two of the currents (I2, I3) are flowing towards the node, while the other two currents (I1, I4) are flowing outwards. The ‘algebraic sum’ needs to take account of this difference in relative direction.

To apply Kirchhoff’s Current Law rigorously, we must first make an arbitrary choice of positive current direction. Suppose currents flowing in to the node (I2, I3) are treated as positive contributions to the algebraic sum (and conversely currents flowing from the node are treated as negative contributions), then the algebraic sum of currents would be written: - I1 + I2 + I3 - I4 , and according to Kirchhoff’s Current Law this algebraic sum is equal to zero:

                - I1 + I2 + I3 - I4 = 0

• Kirchhoff’s Voltage Law (KVL):

        The algebraic sum of  all voltages taken around a closed loop in a circuit is zero.
         This law is also called Loop analysis

The figure shows a circuit loop, which is part of a larger circuit. The loop involves four nodes, ABCD, between which are connected four components. We must recognise that the direction of voltages matters when using Kirchhoff’s Voltage Law.

In this case the four components are resistances, but Kirchhoff’s Voltage Law can be applied no matter what components are connected in the closed circuit loop. The voltages across the four resistances comprising the circuit loop have been defined as V1, V2, V3,V4 and Kirchhoff’s Voltage Law allows us to write down an equationrelating these voltages. 

If we think about travelling around the closed circuit loop in any direction, we note that the four voltages will be encountered in sequence. Two of the voltage arrows will point in the direction of travel and two will oppose the travel. The ‘algebraic sum’ of voltages needs to take account of this difference in relative direction.

To apply Kirchhoff’s Voltage Law correctly, we must make arbitrary choices about the direction of travel around the closed circuit loop and the contribution which the separate voltages make to the algebraic sum around the closed circuit loop. Suppose we travel around the loop in Fig. 2.2 in the clockwise direction (ABCD) and that voltages opposite to the direction of travel make a positive contribution to the algebraic sum. In travelling from A to B the voltage V1 is encountered and it is in a direction which is opposite to the travel. Therefore, V1 is a positive contribution to the algebraic sum. The same comment is true of V2, which is met when proceeding from B to C. However, travelling from C to D and back to A, the voltages V3 and V4 are encountered and in both cases the voltages are in the same direction as the travel, giving a negative contribution to the algebraic sum. 

Expressed mathematically, the algebraic sum of voltages around the closed loop ABCD is: 

            + V1 + V2 - V3 - V4 

and Kirchhoff’s Voltage Law states that this sum is equal to zero:
           + V1 + V2 - V3 - V4 = 0

Recall the Ohm Law that V = IR

 

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Multimeter

Multimeters allow measurement of voltage, current, and resistance. Multimeters may use analog or digital circuits—analog multimeters and digital multimeters. An analogue meter moves a needle along a scale. Switched range analogue multimeters are very cheap but are difficult for beginners to read accurately, especially on resistance scales. Most modern multimeters are digital. Digital meters give an output in numbers, usually on a liquid crystal display.

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OHM’S LAW

An excellent analogy for the simplest of electrical circuits is the water in a hose connected to a pressure valve. Think of the electrons in the copper wire as the water in the hose, the pressure valve as the applied voltage, and the size of the hose as the factor that determines the resistance. If the pressure valve is closed, the water simply sits in the hose without motion, much like the electrons in a conductor without an applied voltage. When we open the pressure valve, water will flow through the hose much like the electrons in a copper wire when the
voltage is applied. 

Current is a reaction to the applied voltage and not the factor that gets the system in motion. The more the rate of water flow through the hose, just as applying a higher voltage to the same circuit will result in a higher current. Ohm’s law in honor of Georg Simon Ohm, clearly reveals that for a fixed resistance, the greater
the voltage (or pressure) across a resistor, the more the current, and the more the resistance for the same voltage, the less the current. In other words, the current is proportional to the applied voltage and inversely proportional to the resistance.

The current I of Eq. results from applying a dc supply of E volts across a network having a resistance R ohm.

Taken from : Introductory Circuit Analysis 10th Edition by Boylestad

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What is capacitor?

Capacitor is an electronic device for storing charge. The simplest type of capacitor: parallel plate capacitor shown as figure; two conducting components (plats) with area S separated by distance d and charged with charge, +q and -q.

 In electronic circuit, capacitor is shown like this

One way to visualize the action of a capacitor is to imagine it as a water tower hooked to a pipe. A water tower "stores" water pressure -- when the water system pumps produce more water than a town needs, the excess is stored in the water tower. Then, at times of high demand, the excess water flows out of the tower to keep the pressure up. A capacitor stores electrons in the same way, and can then release them later.

• Charging

 

 When connected to battery, Plate attached to positive pole of battery will loss electrons. Plate attached to negative pole of battery will receive electrons. Capacitor will have the same voltage as the battery.

• Discharging

 

When a bulb is hooked with the capacitor and the battery is replaced by wire, current will flow from one plat of the capacitor to the other and light the bulb until the capacitor completely discharge.

Capacitor has the same function as battery, but with very different way of work. The difference between a capacitor and a battery is that a capacitor can dump its entire charge in a tiny fraction of a second, where a battery would take minutes to completely discharge itself.

The use of capacitor in connection with other electronic devices:
-Reduces voltage fluctuation in electronic power supply
-A capacitor allows pulse signals to flow
-Made up an oscillator circuit if associated with inductive component
-Filtering specific frequency
-Provide electronic time delay

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Resistor - Color Coding and Standard Value

The flow of charge through any material encounters an opposing force similar in many respects to mechanical friction. This opposition, due to the collisions between electrons and between electrons and other atoms in the material, which converts electrical energy into another form of energy such as heat, is called the resistance of the material. Resistance is measured in Ohms (Ω), the capital Greek letter omega. The circuit symbol for resistance appears in figure below with the graphic abbreviation for resistance (R).

 Most resistors have four coloured band. The first three bands determine the resistance, the fourth band indicates its tolerance. Tolerance is how much the resistance varies drom its specified value, given as percentage : e.g 5% tolerance is indicated by a gold fourth band. It means that a 100 Ohm resistor could actually be between 95-105 Ohm.

E.g., the grey-red-brown-gold resistor is 820 Ohm Resistor.

There are also 5 band resistors. The first four bands determine resistance and the fifth indicates the tolerance generally these are a 1% tolerance resistor, much more accurate than 5% resistor. To determine the resistance, the first three rings are the significant value, the fourth ring is the number of zeros following or multiplier. Eg. 1kOhm is brown-black-black-brown-brown

 

Resource : My lecture note

                  Introductuory Circuit Analysis by Boylestad

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The 555 Timer - Monostable Multivibrator

A Monostable Multivibrator is a circuit that produces an output pulse of fixed duration each time the input of the circuit is triggered. This is useful in producing timing signals. We can use 555 as monostable multivibrator by arranging the 555 timer as shown at picture below.

When the trigger input is slightly less then +Vcc/3, the lower op amp has a high output and reset the flip-flop. This cuts off the transistor allowing capacitor to charge. When the threshold voltage is slightly greater than +2Vcc/3, the upper op amp has a high output, which sets the flip-flop. As soon as Q goes high, it turns on transistor and quickly discharge the capasitor.

The output pulsewidth can be calculated by this formula

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