There are different types of capacitors available in the market. The key factor in distinguishing different types of capacitors is the Dielectric used in its construction. Some of the common capacitor types are ceramic, electrolytic (which include Aluminium capacitors, Tantalum capacitors and Niobium capacitors), plastic film, paper and mica. Each capacitor type has its own advantages and disadvantages. The characteristics and areas of applications may vary from one capacitor to other. Hence, when choosing a capacitor, following few of many factors must be considered. Size: Both the physical dimension and the value of the capacitance is important. Working Voltage: It is an important characteristic of the capacitor. It specifies the maximum voltage that can be applied across the capacitor. Leakage Current: A small amount of current will flow through dielectric as they are not the perfect insulators.  This is called leakage current. Equivalent series resistance: The terminals of the capacitor have a small amount of resistance (usually less than 0.1Ω). This resistance becomes a problem when the capacitor used at high frequencies. These factors determine how and in what applications a particular type of capacitor can be used. For example, the rated voltage of an electrolytic capacitor is larger when compared to a ceramic capacitor in the similar capacitance range. So they are generally used in power supply circuits. Similarly, some capacitors have very low leakage current and others have very high leakage current. Depending on the application, appropriate capacitor should be chosen. Dielectrics in Capacitors           Fixed capacitors are more common types of capacitors. It is difficult to find an electronic circuit without a capacitor. Most of the capacitors are named after the dielectric used in the construction. Some of the common dielectrics used in the construction of capacitors are: Ceramic Paper Plastic film Mica Glass Aluminium Oxide Tantalum Pentoxide Niobium Pentoxide The last three are used in electrolytic capacitors. Despite the use of different kinds of dielectrics in the construction of capacitors, the functionality of the capacitor doesn’t change: to store energy in the form of electric charge between the parallel plates. Table of Contents Variable Capacitors Ceramic Capacitors Class 1 Ceramic Capacitors Class 2 Ceramic Capacitors Film Capacitor Axial Lead Type: Radial Lead Type: Film power capacitors Ceramic Capacitors Polypropylene Capacitor  Polycarbonate capacitor Silver Mica Capacitor Electrolytic Capacitors Electrolytic Capacitor Diagram Aluminum Electrolytic Capacitors Tantalum Electrolytic Capacitors Super-capacitors Variable Capacitors Like resistors, capacitors are also available as fixed and variable types. Variable capacitors are those in which the capacitance can be changed either mechanically or electronically. Such capacitors are generally used in resonant circuits (LC circuits) for tuning radios and impedance matching in antennas. These capacitors are usually called Tuning Capacitors. There is another type of variable capacitors called Trimmer Capacitor. These are fixed on PCB’s and are used for the calibration of the equipment. They are non-polarised capacitors and are very small in size. They are generally not available for the use of regular customer. The capacitance of variable capacitors is very small which is usually in the order of few picofarads (generally less than 500pF). Mechanical variable capacitors consist of a set of semi-circular metal plates fixed on the axis of a rotor. This setup is placed between a set of stator metal plates. The overall capacitance value (C) for this type of capacitors is determined according to the position of the moving metal plates with respect to the fixed metal plates. When the axis is turned, the area of overlap between the stator plates and rotor plates will vary and the capacitance is changed. In this design, when the two sets of metal plates are fully meshed together , the capacitance value is generally at maximum value. High voltage type tuning capacitors have large air-gaps or spaces between the plates with relatively large break down voltages in order of kilo volts. For this reason these dielectric capacitors are very useful in tuning circuits. Mechanical variable capacitors generally use air or plastic foils as dielectric. But the use of vacuum variable capacitors is increasing as they provide better working voltage range and higher current handling capabilities. The capacitance in case of mechanically tuned capacitors can be varied using the screw on the top of the capacitor. In case of electronically controlled variable capacitors, a reverse biased diode is used in which the thickness of the depletion layer will vary according to the applied DC voltage. Such diodes are called as Variable Capacitance Diodes or simply Varicaps or Varactors. Ceramic Capacitors Ceramic capacitors are the most used capacitors in the electronics industry. They are also the most produced capacitors with over 1000 billion units being produced every year. The name comes from the ceramic material which is the dielectric used in its construction. Ceramic capacitors are fixed capacitance type capacitors and they are usually very small (in terms of both physical dimensions and capacitance). The capacitance of ceramic capacitors is usually in the range of picofarads to few micro farads (less than 10µF). They are non-polarised type capacitors and hence can be used in both DC as well as AC circuits. The construction of these types of capacitors is very simple. A small ceramic disc is coated with silver on either side. Hence they are also called as Disc Capacitors. The ceramic acts as dielectric (insulator) and the silver coating will form the electrodes. The thickness and the composition of the ceramic layer will determine the electrical properties of the capacitor. In order to achieve large capacitance values, multiple layers of such disc are stacked to form a multi-layer ceramic chip capacitor (MLCC). Modern electronics generally comprise of MLCC capacitors. The capacitance of the ceramic capacitors is large when compared to their size. In order to achieve this large capacitance, the dielectric constant of ceramic capacitors is very high. Ceramic capacitors are divided into two classes based on the areas of applications. Class 1 Ceramic Capacitors Often used in resonant circuits because of their high stability and low loss. The most common type of ceramic used in class 1 capacitor is made from Titanium dioxide (TiO2) with small portions of Zinc, Magnesium used as additional compounds. These are added in order to achieve the maximum possible linear characteristics. Class 1 capacitors have low permitivity and hence the efficiency in terms of volume is relatively low. Therefore, the capacitance range of class 1 capacitors is low. The electrical losses of class 1 capacitors are very low and the dissipation factor is 0.15 percent. The value of the capacitance is independent of the applied voltage. They have a liner temperature coefficient. All these characteristics of class 1 ceramic capacitors make them useful in the applications like filters with high Q factor and oscillator circuits like PLL’s. There is no fear of aging of class 1 ceramic capacitors. Class 2 Ceramic Capacitors Often used in buffers, coupling circuits and by-pass systems because of their high efficiency in terms of volume. This high volume efficiency is because of their high permittivity. The capacitance of class 2 capacitors will depend on the applied voltage and has a non-linear change for temperature changes. The accuracy and stability are less when compared to class 1 ceramic capacitors. The ceramic for class 2 capacitors is made from ferro electric materials like Barium Titanate (BaTiO­3­) with additives like silicates of aluminium or magnesium and oxide of aluminium. Because of the high permittivity in class 2 capacitors, high capacitance values are possible with smaller size than class 1 capacitors of same rated voltage. Hence, they are used in buffers, filters and coupling circuits where the capacitor is required to maintain a minimum capacitance. Class 2 capacitors can age over time. Another class of ceramic capacitors is also available called Class 3 with higher permittivity and better volumetric efficiency. But the electrical characteristics of this class are worse along with poor accuracy and stability. Generally, ceramic capacitors have less ESR (Equivalent series resistance) and leakage current when compared to electrolytic capacitors. The working voltage of class 1 ceramic capacitors is up to 1000V and that in class 2 ceramic capacitors is up to 2000V. The main advantage of ceramic capacitors is that there are no coils inside its structure and so there is no inductance factor introduced during circuit operation. Hence, ceramic capacitors are suitable for high frequency applications. Ceramic capacitors are available in normal two leaded through-hole structures, surface mount (SMT) multi layer mode and special lead less disc capacitors that are designed particularly for PCB’s. Both the through-hole and surface mount ceramic capacitors are frequently used. Ceramic capacitors are normally having a 3-digit number coded on their body to identify the capacitance value generally in picofarads (pF). In that, the first two digits are used to indicate the capacitance value and the third digit indicates the number of zeros to be added. For example a ceramic capacitor with the markings 153 would indicate 15 and 3 zero’s in picofarads which is equivalent to15, 000 pF or 15nF. Film Capacitor Film capacitors are the most commonly used type of capacitors among all types of capacitors which have the difference in their dielectric properties. Film capacitors are the capacitors with an insulating plastic film as its dielectric and these are non-polarized capacitors. The dielectric materials for these capacitors are existed in the form of a thin layer which is provided with metallic electrodes and it is wounded in to a cylindrical winding. The both electrodes of film capacitors may be zinc or metalized aluminium. The main advantage of film capacitor is direct connection between its internal construction and its electrodes on both ends of the winding. This direct contact with electrodes causes to keep all current paths to become short.This design behaves like a large number of individual capacitors connected in parallel. And also this type of capacitors structure results in low ohmic losses and the low parasitic inductances . These film capacitors are used in AC power applications and also used in the high frequency applications. Some of the examples of plastic films which are used as dielectric for the film capacitors are Polypropylene, Polyethylene naphthalate, Polyester, Polyphenylene sulfide and Polytetrafluoroethylene. Film type capacitors are in the market with capacitance value ranges from 5pF to 100uF .Film Film capacitors also available in different shapes and different styles which include, Wrap & Fill (Oval and Round) type: In this type the capacitor ends are sealed with epoxy and the capacitor is wrapped in a tight plastic tape. Epoxy Case (Rectangular & Round): In this type capacitors are encased in a moulded plastic shell and it is filled with epoxy. Metal Hermetically Sealed (Rectangular & Round): These types of capacitors are encased in a metal tube or can, and sealed with epoxy. In present days the above all case style capacitors are available in both the types Radial and Axial Leads. The main advantage of the plastic film capacitors is that, they operate well and good at high temperatures when compared to other paper types. These capacitors have small tolerance, high reliability and also they have very long service life. Examples of film type capacitors are cylindrical film, rectangular metalized film and foil film types. They are given below. Axial Lead Type: Radial Lead Type: Figure 4.Foil type film capacitors. These film types of capacitors require much thicker dielectric material in order to avoid the punctures and tears in the dielectric film. Hence these are suited for low capacitance value and large sizes. Film power capacitors Film power capacitors are also called as Power film capacitors.The construction techniques and materials which are used for large power film capacitors are usually similar to those of the ordinary film capacitors. However these capacitors with high power ratings are used in the applications of power systems and electrical installations. Power film capacitors are used in variety of applications. These capacitors serve as snubbing or damping capacitors when connected a resistor in series with it. These are also used in close tuned or low detuned filter circuits for filtering the harmonics and also used as pulse discharge capacitors. Ceramic Capacitors Ceramic capacitors are also called as “Disc-capacitors”. Like electrolytic, these are also the mostly used type of capacitors. A ceramic capacitor is constructed with two or more alternating layers of ceramic and a metal Here the ceramic acts as its dielectric and metal acts as its electrodes. These ceramic capacitors are non-polarized fixed type capacitors. Generally the electrical behavior of the ceramic material can be divided into two classes related to its stability. They are given and explained below. Class 1: ceramic capacitors with high stability and low losses for compensating the influence of temperature in resonant circuit applications. Class 2: These types of capacitors offer high volumetric efficiency for buffer by pass and coupling applications. Ceramic types of capacitors are normally having a 3-digit number coded on their body to identify the capacitance value generally in pico-farads (pF). In that the first two digits are used to indicate the capacitors value and the third digit indicates the number of zeros to be added. For example a ceramic capacitor with the markings 153 would indicate 15 and 3 zero’s in pico-farads which is equivalent to 15 , 000 pF or 15nF. Polypropylene Capacitor  Polypropylene capacitor is one of the many varieties of film type capacitors. Polypropylene capacitors are the capacitors that have a polypropylene film as their dielectric. Polypropylene capacitors are available within the capacitance ranges from 100 pf to 10µF. The main feature of Polypropylene Capacitor is high working voltages up to 3000 V. This feature makes polypropylene (pp) capacitors useful in circuits in which operating voltages are typically very high, such as power amplifiers particularly valve amplifiers, power supply circuits and TV circuits. Polypropylene capacitors are used when a better tolerance is needed than what a polyester capacitor can provide. Polypropylene capacitors are also used in coupling and storage applications due to their high isolation resistance values. And also they have stable capacitance values for frequencies below 100KHZ. These polypropylene capacitors are used in the applications where we need to perform the tasks of noise suppression, coupling, filtering timing, blocking, bypassing, and handling pulses. Polycarbonate capacitor Polycarbonate capacitors are the capacitors that have a polycarbonate material as its dielectric. These types of capacitors are available within the capacitance range of 100pF to 10µF and have the working voltages up to 400V DC. These polycarbonate capacitors can operate with a temperature range of -55°C to +125°C without de-rating. These capacitors have very good temperature coefficients, due to these reason polycarbonate capacitors are preferable. These capacitors are not used in the high-precision applications because of their high tolerance levels of 5% to 10%. The polycarbonate capacitors are also used for AC applications. Sometimes they are also found in switching power supplies. Ceramic capacitors are also called as “Disc-capacitors”. Like electrolytic, these are also the mostly used type of capacitors. A ceramic capacitor is constructed with two or more alternating layers of ceramic and a metal Here the ceramic acts as its dielectric and metal acts as its electrodes. These ceramic capacitors are non-polarised fixed type capacitors. Generally the electrical behavior of the ceramic material can be divided into two classes related to its stability. They are given and explained below. Silver Mica Capacitor Silver Mica Capacitors are capacitors that are made from depositing a thin layer of silver on a mica material as its dielectric.The reason for the use of silver mica capacitors is that their high performances compared to any other type of capacitors. Silver mica capacitors can be obtained with the tolerance of +/- 1%. This is much better than any other type of capacitor which is available in today’s market. The temperature co-efficient of silver mica capacitors is much better than other types of capacitors. And this value is positive and it is normally in the region of 35 to 75 ppm / C, with an average value of +50 ppm / C. Capacitance values for silver mica capacitors are normally in the range between a few pico-farads to 3300 pico -farads.Silver mica capacitors have very high levels of Q and also have small power factors. The silver mica capacitors have the voltage range between 100V to 1000 V. Silver mica capacitors are used in RF oscillators.The silver mica capacitors are not used in coupling and decoupling applications because of their high cost.  Due to their size, cost and also the improvements in other types of capacitors these are not used nowadays. Electrolytic Capacitors Electrolytic Capacitors are generally used in the applications where very large capacitance values are required. The electrolytic capacitors have a metallic anode covered with an oxidized layer generally used as its dielectric. Another electrode of a capacitor is a non-solid or solid electrolyte. Most of the electrolytic capacitors are polarized. These capacitors are categorized according to their dielectric material. Mainly these are categorized in to three classes, they are given as Aluminium electrolytic capacitors: Here aluminium acts as its dielectric. Tantalum electrolytic capacitors: Here tantalum pent oxide acts as its dielectric. Niobium electrolytic capacitors:Here niobium pent oxide acts as its dielectric Usually the permittivity of tantalum pent oxide is almost three times greater than the permittivity of aluminum dioxide, but this permittivity determines only the dimensions. Generally three types of electrolytes are used.They are as follows: Non solid (wet or liquid): These capacitors have the conductivity nearly 10ms/cm and these are available with low cost. Solid manganese oxide: These capacitors have the conductivity nearly 100ms/cm and also have high quality and stability. Solid conductive polymer: These type of capacitors have conductivity approximately 10000 ms/cm and also the ESR values of <10mΩ. Electrolytic Capacitors are generally used in direct (DC) power supply circuits. These are also used in the applications of coupling and decoupling to reduce ripple voltage, due to their large capacitance values and their small size. One of the main disadvantages of electrolytic capacitors is their low voltage ratings. Electrolytic Capacitor Diagram Aluminum Electrolytic Capacitors Aluminum Capacitors are capacitors that are made of oxide film on aluminum foils with a strip of absorbent paper between them which is soaked in an electrolyte solution and all these design can be sealed in a can. Basically there are two types of Aluminum Electrolytic Capacitors they are plain foil type and etched foil type. Plain foil type electrolytic capacitors are mainly used as smoothing capacitors in power supply circuits while etched foil type capacitors used in coupling DC blocking and by pass circuits. Electrolytic aluminum capacitors cover the capacitance range of1uF to 47000uF and large tolerance of 20%. The working voltage ratings range up to 500V.These are cheaper and easily available in the market. The capacitance value and voltage ratings are either printed in uF’s or coded by a letter followed by three digits. These three digits represent the capacitance value in pF where first two digits represent the number and the third one is the multiplier digit. Tantalum Electrolytic Capacitors Tantalum Capacitors are capacitors that are made of tantalum pent oxide as its dielectric material. Tantalum electrolytic capacitors are also polarised capacitors like aluminum capacitors.Tantalum electrolytic capacitors are obtained in both the types of wet (foil) and dry (solid). The second terminal of tantalum electrolytic capacitors is smaller than the terminal of equivalent aluminum capacitors and that terminal is made with manganese dioxide. The main advantage of Tantalum Electrolytic Capacitorsover aluminum capacitors is that they are more stable, lighter and smaller. They have capacitance values range from 47nF to 470uF and maximum working voltage up to 50V.These are costlier than aluminum electrolytes. The properties of the tantalum oxide dielectric are low leakage current and better capacitance stability. These properties oftantalum oxide dielectric cause to use them in blocking, by-passing, decoupling, filtering and timing applications. And also these properties are much better than the dielectric of aluminum oxide. Super-capacitors The super- capacitor is also known as ultra-capacitor or electric double-layer capacitor. These capacitors are made with a thin electrolyte separator which is flanked with activated carbon ions. It differs from a regular capacitor,the capacitance value of a super capacitor is very high and it is in order of milli farads with the voltage ranges of 2.3V to 2.75V. Super capacitors are categorized into three types based on their electrode design they are Double-layer capacitors: These capacitors have carbon electrodes or their derivatives. Pseudo capacitors: These capacitors have metal oxide or conducting polymer electrodes. Hybrid capacitors: These capacitors have asymmetric electrodes. Ceramic capacitors are also called as “Disc-capacitors”. Like electrolytic, these are also the mostly used type of capacitors. A ceramic capacitor is constructed with two or more alternating layers of ceramic and a metalHere the ceramic acts as its dielectric and metal acts as its electrodes. These ceramic capacitors are non-polarised fixed type capacitors. Generally the electrical behavior of the ceramic material can be divided into two classes related to its stability. They are given and explained below. batteries.

Circuit Schematic As can be seen in the figure above, the IC 555 is configured as an astable whose pin#2 is used for sensing the proximity or the capacitance of a human hand. Pin#2 is terminated with a metallic plate (which could be replaced by the faucet body) such that whenever somebody approaches the tap for washing hands, the sensor is triggered activating the connected relay. The relay finally opens the tap valve for releasing water. However in the above design the relay is supposed to remain activated only for a short duration of time, which means the individual might require to move his hand to and fro frequently if the washing is required to be for a relatively prolonged period. Another design which is shown below can be executed for the same: A Improved Faucet Control Schematic The above shown proximity detector circuit is a transistor based design and is designed to sense a human hand when brought at a relatively close proximity to the indicated plate. Circuit Description The T1, and T2 transistors are rigged quite in the manner like a Darlington pairs forming a high gain detector stage. The capacitive plate attached with the base of T1 sense the minute potential differences due to the variations in the capacitance of the plate in response to the human hand and conducts some current at its emitter lead, which is picked by T2 and amplified to a greater extent across its collector lead. This preamplified signal is detected by the FET stages, which further amplify it to a level strong enough to cause the relay to toggle. Since the proposed touch free faucet design is an electrically activated device, the water control mechanism needs to be implemented through a water valve mechanism, such as a 12V solenoid valve system. A typical 12V solenoid valve system can be witnessed below: Integrating a 12V Solenoid The two leads are supposed to be fed with a switchable 12V supply in order to close and open the water passage through the white plastic pipe. The white plastic pipe needs to be inserted in series with the faucet water transmission line so that the water supply from the faucet is appropriately controlled via the above discussed operations.

As we all know a laptop runs using a DC potential from an in built Li-Ion battery just as our cell phones do. Normally we utilize a AC DC adapter for charging a laptop battery in homes and offices, these adapters are actually SMPS power supplies rated with the required and matching specs of the laptop battery. However the above power supply units work only with AC supplies, and in places where an AC outlet may be available. These units will not work in places where an AC source is not present such as in cars and other similar vehicles. A novel little circuit presented here will allow a laptop battery to be charged even from a DC source such as a car or truck batteries (12V). It's a very simple, cheap, versatile and universal circuit which may be dimensioned for charging all types of laptops by adjusting the relevant components provided in the circuit. It's a simple plug and play charger circuit. Normally most of the laptop adapters are rated at 19V/3.5Amps, however some may be rated at higher currents for facilitating fast charging. PWM Charging Control The discussed circuit has a voltage adjustment features (via PWM) which may be suitably adjusted as per the required  specs. The current may be suitably safeguarded by adding a 3 ohm 5 watt resistor at the output positive terminal. As can be seen in the circuit diagram, the design is basically a powerful DC to DC voltage doubler circuit which utilizes a push pull mosfet stage for the required boosting of the voltage. The circuit requires an oscillator stage for initiating the proposed operations which is configured around IC1a. The components R11, R12, C5 along with the two diodes becomes a neat little PWM controller which sets the duty cycle of the entire circuit and can be used for adjusting the output voltage of the circuit. Typically the circuit would generate around 22V from a 12V source, by adjusting R12 the output may be tailored to an exact 19V, which is the required laptop charging voltage.

The Circuit Design The function of  the various components used across the various stages of the above shown voltage controlled transformerless power supply circuit may be understood from the following points: The mains voltage is rectified by the four 1N4007 diodes and filtered by the 10uF/400V capacitor. The output across the 10uF/400V now reaches around 330V which is the peak rectified voltage achieved from the mains. The voltage divider network configured at the base of the TIP122 makes sure that this voltage is reduced to the expected level or as required across the power supply output. If a 12V is required the 10K pot may be set to achieve this across the emitter/ground of the TIP122. The 220uF/50V capacitor ensures that during switch ON the base is rendered a momentary zero voltage in order to keep it switched OFF and safe from the initial surge in-rush. The inductor further ensures that during the switch ON period the coil offers a high resistance and stops any inrush current to get inside the circuit, preventing a possible damage to the circuit. For achieving a 5V or any other attached stepped down voltage, a voltage regulator such as the shown 7805 IC may be used for achieving the same. Circuit Schematic

Here are diagrams for a couple of typical amp installations to help you see how all the separate components fit together to form a car audio system. The first diagram shows a total system upgrade using an aftermarket receiver, two amplifiers, and a subwoofer. The second is more specific. It shows you how to add a subwoofer to a factory system. How to wire a full car audio system  This wiring diagram shows how a full-blown car audio system upgrade gets wired in a car. The system depicted includes new speakers, an aftermarket receiver, a 4-channel ampfor the front and rear pairs of full-range speakers, and a mono amp for a subwoofer. The extra gear you'll need for wiring the amps includes: a dual amplifier wiring kit distribution blocks speaker wire RCA cables Capacitors aren't usually necessary in a car stereo installation but we included one here to show how it would get wired into a system. How to add a subwoofer to a factory stereo A lot of folks want to add bass to their system without replacing the factory radio, either because it looks good or is impossible to replace. The following wiring diagram shows the additional wiring you'll need to add a subwoofer to a factory system. Start by getting a subwoofer amplifier or powered sub with speaker-level inputs. You'll need these items for the installation and to give it that professional touch:   Use wire taps to get signal An Add A Fuse connector plus a 2A to 10A fuse to get the amp's remote turn-on voltage An amp wiring kit and some speaker wire

The relay is an electromagnetically operated switch, where with a low level input current, typically in the range of 100 mA and 150 mA, can be switched high level current up to 80 A, in some cases and more. When the input current flows through the copper coil, the magnetic field is generated and the hinged soft iron plate is fast attracted, which in turn is mechanically connected to the one movable contact of the switch (see figure 1 below). The other contact of the switch is non-movable (stationary contact), placed at very short distance next to the movable contact. Depending on the relay type, the switch contacts can be normally open or normally closed. The number of poles refers to the number of switches, so a single pole relay has one switch. Different Types of Single-Pole Relays On figure 1 is shown a typical single-pole normally open relay, where the contacts are normally open when the relay is not activated (OFF), i.e. coil is not energized. When the relay is activated (ON), i.e. coil is energized, in that case the contacts are closed (contacts 8 and 9 are connected), so the relay switch is switched ON. Figure 1. Single-pole normally open relay: 1. Housing 2. Pole piece 3. Return spring 4. Copper coil 5. Hinge 6. Flexible copper braid 7. Soft iron core 8. Movable electrical contact 9. Non-movable electrical contact On figure 2 is shown a typical single-pole normally open tied pin relay. When the relay is not activated (OFF) the contacts are normally open. When the relay is activated (ON), in that case the contacts are closed, i.e. the relay switch is switched ON. Figure 2. Single-pole normally open tied pin relay: 1. Housing 2. Pole piece 3. Return spring 4. Copper coil 5. Hinge 6. Flexible copper braid 7. Soft iron core 8. Movable electrical contact 9. Non-movable el. contact with two pins On Figure 3 is shown a typical single-pole normally closed relay. When the relay is not activated (OFF) the contacts are normally closed (connected 8 and 9). When the relay is activated (ON), in that case the contacts are open.  Figure 3. Single-pole normally closed relay: 1. Housing 2. Pole piece 3. Return spring 4. Copper coil 5. Hinge 6. Flexible copper braid 7. Soft iron core 8. Movable electrical contact 9. Non-movable electrical contact On figure 4 is shown a typical single pole changeover relay. In this case, the contact A is normally open and the contact B is normally closed. When the relay is not activated (OFF) the contact A is open (switched OFF), and the contact B is closed (switched ON). When the relay is activated (ON), the contact A is closed (switched ON), and the contact B is open (switched OFF). Figure 4. Single-pole changeover relay: 1. Housing 2. Pole piece 3. Return spring 4. Copper coil 5. Hinge 6. Flexible copper braid 7. Soft iron core 8. Non-movable el. contacts (A and B) 9. Movable electrical contact Specifications, Characteristics, Wiring Symbols and Marking of Relay Pin The relays are usually supplied with 12 V directly from the vehicle battery. The electrical resistance (impedance) of the coil is vary and is different depending upon the manufacturer of the relay as well as relay’s type, but in general a typical value should be expected between 50 ohms and 200 ohms. Input current typically is in the range between 100 mA and 150 mA. Figure 5 shows the usual marking of pins (terminals) and layout for a single-pole normally open relay. The mainly, marking of pins are with numbers given in wiring symbols below. Sometimes pin numbering (marking) can be different, for example with numbers 1, 2, 3, 4 or similar. In that case, to find out the pins, must follow the relay symbol scheme, which is usually drawn on the top or on the side of the relay housing. Figure 5. Single-pole normally open relay: Pin 85 negative electric pole of the coil (mass) Pin 86 positive electric pole of the coil (command signal) Pin 30 permanent plus 12V Pin 87 switched plus When on pin 86 is brought a command signal the relay is activated (ON). In that case the switching contacts are closed (pin 30 and pin 87 are connected), so the switch is switched ON. Some vehicle/engine management systems require to be used a resistor (R) to limit the current flow through the coil or the use of a diode (D) to dissipate the stored energy in the coil. In both cases the layout of pins are same and are shown on figure 5. NOTE: The relay types without integrated diode may work even if the coil pins are connected opposite (doesn't matter where is connected positive, i.e. negative pole of the coil pins). But, in the case when is used relay with integrated diode, you must be careful how connecting the relay, pin 85 to negative, and pin 86 to positive pole. If you connect opposite, it may produce a fuse breakdown or some other element breakdown into the related electrical circuit where the relay is connected. Figure 6 shows the standard marking of pins and layout for a single pole normally open tied pin relay. The construction and pin numbering can vary depending upon the manufacturer. Figure 6. Single-pole normally open tied pin relay: Pin 85 negative electric pole of the coil (mass) Pin 86 positive electric pole of the coil (command signal) Pin 30 permanent plus 12V Pin 87 or 87b switched plus (tied pin) When on pin 86 is brought a command signal the relay is activated (ON). In that case the switching contacts are closed (pin 30 and tied pin 87 are connected), so the switch is switched ON. Figure 7 shows the standard marking of pins and layout for a single-pole normally closed relay. Figure 7. Single-pole normally closed relay: Pin 85 negative electric pole of the coil (mass) Pin 86 positive electric pole of the coil (command signal) Pin 30 permanent plus 12V Pin 87 switched plus This type of relay works opposite than previous types. In normal position when coil is without command signal (not activated), the switching contacts are closed (pin 30 and pin 87 are connected), i.e. the switch is switched ON. When on pin 86 is brought a command signal the relay is activated. In that case, the switching contacts are open (pin 30 and pin 87 are disconnected), so the switch is switched OFF. Figure 8 shows the standard marking of pins and layout for a single pole changeover relay. The construction and pin numbering can vary depending upon the manufacturer. Figure 8. Single-pole changeover relay: Pin 85 negative electric pole of the coil (mass) Pin 86 positive electric pole of the coil (command signal) Pin 30 permanent plus 12V Pin 87 switched plus (normally open) Pin 87a switched plus (normally closed) In this case, at normal position when coil is without command signal (not activated) the pin contact 87 is normally open (switched OFF), and the contact 87a is normally closed (switched ON). When the relay is activated with a command signal, the contact 87 is closed (switched ON), and the contact 87a is open (switched OFF). Rarely, in some cases can be found a relay type with an integral fuse added for protection. This type is shown below. Figure 9. Single-pole relay type with an integral fuse: Pin 85 negative electric pole of the coil (mass) Pin 86 positive electric pole of the coil (command signal) Pin 30 permanent plus 12V Pin 87 switched plus Diagnostics and Testing Procedures • Check that there is any “clicking” sound at the moment of the activating the relay. • Check the condition of the wires and terminals (corrosion, overheating, toughness of terminals, etc.). • Unplug the relay and check the electrical resistance of the coil (between the pins 85 and 86). The resistance should be roughly between 50 ohms and 200 ohms. If the reading is drastically out from these values, as well as the two extreme values: zero, or infinite, is required replacement. • Check that there is an open circuit (infinite resistance) between the switch terminals (30 and 87) for a normally open relay when the coil is not energized (relay is not activated/OFF). • Check that there is continuity between the switch terminals (30 and 87) for a normally open relay when the coil is energized (relay is activated/ON). See figure 10. Figure 10. Testing procedure: Connect pin 85 and one pin from light to the negative (minus) pole of the battery, as well as pin 87 to the other pin of light. Then connect pins 30 and 86 to the positive (plus) pole of the car battery. If relay working properly, then the light must be switched ON. If you disconnect 86 or 85, then the light should be switched OFF. NOTE: The relay types without integrated diode can work and you can test even if the pin 85 and pin 86 are connected opposite, but at the relays with integrated diode, you must be careful how connecting the relay when testing! Pin 85 must be connected to the negative pole, and pin 86 must be connected to the positive pole of the car battery.

Solar concept is not new for us. As non-renewable energy sources are decreasing, usage of solar energy is increased. This solar energy is not only used on the Earth but also used in space stations where no electrical power is available. Here is the simple circuit to charge 12V, 1.3Ah rechargeable Lead-acid battery from the solar panel. This solar charger has current and voltage regulation and also has over voltage cut off facilities. This circuit may also be used to charge any battery at constant voltage because output voltage is adjustable. Specifications of the Charging Circuit Solar panel rating – 5W /17V Output Voltage –Variable (5V – 14V). Maximum output current – 0.29 Amps. Drop out voltage- 2- 2.75V. Voltage regulation: +/- 100mV Solar Battery Charger Circuit Principle: Solar battery charger operated on the principle that the charge control circuit will produce the constant voltage. The charging current passes to LM317 voltage regulator through the diode D1. The output voltage and current are regulated by adjusting the adjust pin of LM317 voltage regulator. Battery is charged using the same current. Circuit Components Solar panel – 17V LM317 voltage regulator DC battery Diode – 1n4007 Capacitor – 0.1uF Schottky diode – 3A, 50V Resistors – 220, 680 ohms Pot – 2K Connecting wires Solar Battery Charger Circuit Design Circuit must have adjustable voltage  regulator , so Variable voltage regulator LM317 is selected. Here LM317 can produce a voltage from 1.25 to 37 volts maximum and maximum current of 1.5 Amps. Adjustable Voltage regulator has typical voltage drop of 2 V-2.5V .So Solar panel is selected such that it has more voltage than the load. Here I am selecting 17v/5w solar panel. Lead acid battery which is used here has specification of 12v/1.3Ah. In order to charge this battery  following are required. Schottky diode is  used to protect the LM317 and panel from reverse voltage generated by the battery when it is not charging. Any 3 A diode  can be used here. For Charging 12V Battery Output voltage Set the output voltage to 14.5 volts(This voltage is specified on the battery as cycle use.) Charging current Charging current = Solar panel wattage/Solar Panel Voltage = 5 / 17 = 0.29A. Here LM317 can provide current upto 1.5A .So it is recommended to use high wattage panels if more current is required for your application.(But here my battery requires initial current less than 0.39Amps. This initial current is also mentioned on the battery). If the battery requires initial current more than 1.5A,it is not recommended to use LM317. Time taken for charging Time taken for charging = 1.3Ah/0.29A = 4.44hours. Power dissipation  Here solar panel has 5Watts Power going into battery = 14.5*0.29 =4 watts Thus 1 watt of  power  going  into  regulator. All the above mentioned parameters have to be taken into account before charging a battery. For 6V Application Set the output voltage to 7.5-8 volts as specified on the battery. calculate the charging current ,power dissipation as shown above. Power Dissipation In this project, power is limited because of the thermal resistance of LM317 voltage regulator and the heat sink. To keep the temperature below 125 degree Celsius, the power must be limited to 10W. LM317 voltage regulator internally has temperature limiting circuit so that if it gets too hot, it shuts down automatically. When battery is charging, heat sink becomes warm. When completing the charging at maximum voltage, heat sink runs hot. This heat is because of excess power that not needed in the process of charging a battery. Current Limiting: As the solar panel provides constant current, it acts as a current limiter. Therefore the circuit does not need any current limiting. Solar Charger Protection: In this circuit, capacitor C1 protects from the static discharge. Diode D1 protects from the reverse polarity. And voltage regulator IC provides voltage and current regulation. Solar Charger Specifications: Solar panel rating: 20W (12V) or 10W (6V) Vout range: 5 to 14V Maximum power dissipation: 10W (includes power dissipation of schottky diode) Typical drop out value: 2 to 2.75V (depends on load current) Max current: 1.5A (internally it limited to 2.2A) Voltage regulation: +/- 100mV How to Operate this Solar Battery Charger Circuit? Give the connections according to the circuit diagram. Place the solar panel in sunlight. Now set the output voltage by adjusting pot RV1 Check the battery voltage using digital multi meter. Solar Battery Charger Circuit Advantages: Adjustable output voltage Circuit is simple and inexpensive. Circuit uses commonly available components. Zero battery discharge when no sunlight on the solar panel. Solar Battery Charger Circuit Applications: This circuit is used to charge Lead-Acid or Ni-Cd batteries using solar energy. Limitations of this Circuit: In this project current is limited to 1.5A. The circuit requires high drop-out voltage.

High-frequency circuit design must account for two important though somewhat mysterious phenomena: reflections and standing waves. We know from our exposure to other branches of science that waves are associated with special types of behavior. Light waves refract when they move from one medium (such as air) into a different medium (such as glass). Water waves diffract when they encounter boats or large rocks. Sound waves interfere, resulting in periodic variations in volume (called “beats”). Electrical waves are also subject to behavior that we usually do not associate with electrical signals. The general lack of familiarity with the wave nature of electricity is not surprising, though, because in numerous circuits these effects are negligible or nonexistent. It is possible for a digital or low-frequency-analog engineer to work for years and design many successful systems without ever acquiring a thorough understanding of the wave effects that become prominent in high-frequency circuits. An interconnect that is subject to special high-frequency signal behavior is called a transmission line. Transmission-line effects are significant only when the length of the interconnect is at least one-fourth of the signal wavelength; thus, we don’t have to worry about wave properties unless we are working with high frequencies or very long interconnects. Reflection Reflection, refraction, diffraction, interference—all of these classic wave behaviors apply to electromagnetic radiation. But at this point we’re still dealing with electrical signals, i.e., signals that have not yet been converted by the antenna into electromagnetic radiation, and consequently we only have to concern ourselves with two of these: reflection and interference. We generally think of an electrical signal as a one-way phenomenon; it travels from the output of one component to the input of another component, or in other words, from a source to a load. In RF design, however, we must always be aware of the fact that signals can travel in both directions: from source to load, certainly, but also—because of reflections—from load to source. The wave traveling along the string experiences reflection when it reaches a physical barrier. A Water-Wave Analogy Reflections occur when a wave encounters a discontinuity. Imagine that a storm has resulted in large water waves propagating through a normally calm harbor. These waves eventually collide with a solid rock wall. We intuitively know that these waves will reflect off the rock wall and propagate back out into the harbor. However, we also intuitively know that water waves breaking onto a beach will rarely result in significant reflection of energy back out into the ocean. Why the difference? Waves transfer energy. When water waves are propagating through open water, this energy is simply moving. When the wave reaches a discontinuity, though, the smooth movement of energy is interrupted; in the case of a beach or a rock wall, wave propagation is no longer possible. But what happens to the energy that was being transferred by the wave? It cannot disappear; it must be either absorbed or reflected. The rock wall does not absorb the wave energy, so reflection occurs—the energy continues propagating in wave form, but in the opposite direction. The beach, however, allows the wave energy to dissipate in a more gradual and natural way. The beach absorbs the wave’s energy, and thus minimal reflection occurs. From Water to Electrons Electrical circuits also present discontinuities that affect wave propagation; in this context, the critical parameter is impedance. Imagine an electrical wave traveling down a transmission line; this is equivalent to the water wave in the middle of the ocean. The wave and its associated energy are propagating smoothly from source to load. Eventually, though, the electrical wave reaches its destination: an antenna, an amplifier, etc. We know from a previous page that maximum power transfer occurs when the magnitude of the load impedance is equal to the magnitude of the source impedance. (In this context “source impedance” can also refer to the characteristic impedance of a transmission line.) With matched impedance, there really is no discontinuity, because the load can absorb all of the wave’s energy. But if the impedance are not matched, only some of the energy is absorbed, and the remaining energy is reflected in the form of an electrical wave traveling in the opposite direction. The amount of reflected energy is influenced by the seriousness of the mismatch between source and load impedance. The two worst-case scenarios are an open circuit and a short circuit, corresponding to infinite load impedance and zero load impedance, respectively. These two cases represent a complete discontinuity; no energy can be absorbed, and consequently all the energy is reflected. The Importance of Matching If you’ve even been involved in RF design or testing, you know that impedance matching is a common topic of discussion. We now understand that impedance must be matched to prevent reflections, but why so much concern about reflections? The first problem is simply efficiency. If we have a power amplifier connected to an antenna, we don’t want half of the output power to be reflected back to the amplifier. The whole point is to generate electrical power that can be converted into electromagnetic radiation. In general, we want to move power from source to load, and this means that reflections must be minimized. The second issue is a bit more subtle. A continuous signal transferred through a transmission line to a mismatched load impedance will result in a continuous reflected signal. These incident and reflected waves pass each other, going in opposite directions. Interference results in a standing wave, i.e., a stationary wave pattern equal to the sum of the incident and reflected waves. This standing wave really does create peak-amplitude variations along the physical length of the cable; certain locations have higher peak amplitude, and other locations have lower peak amplitude. Standing waves result in voltages that are higher than the original voltage of the transmitted signal, and in some cases the effect is severe enough to cause physical damage to cables or components. Summary Electrical waves are subject to reflection and interference. Water waves reflect when they reach a physical obstruction such as a stone wall. Similarly, electrical reflection occurs when an AC signal encounters an impedance discontinuity. We can prevent reflection by matching the load impedance to the characteristic impedance of the transmission line. This allows the load to absorb the wave energy. Reflections are problematic because they reduce the amount of power that can be transferred from source to load. Reflections also lead to standing waves; the high-amplitude portions of a standing wave can damage components or cables.

Introduction Digital, or boolean, logic is the fundamental concept underpinning all modern computer systems. Put simply, it’s the system of rules that allow us to make extremely complicated decisions based on relatively simple “yes/no” questions. Digital circuitry Digital logic circuits can be broken down into two subcategories- combinational and sequential. Combinational logic changes “instantly”- the output of the circuit responds as soon as the input changes (with some delay, of course, since the propagation of the signal through the circuit elements takes a little time). Sequential circuits have a clock signal, and changes propagate through stages of the circuit on edges of the clock. Typically, a sequential circuit will be built up of blocks of combinational logic separated by memory elements that are activated by a clock signal. Programming Digital logic is important in programming, as well. Understanding digital logic makes complex decision making possible in programs. There are also some subtleties in programming that are important to understand; we’ll get into that once we’ve covered the basics. Combinational Logic Combinational circuits are built of five basic logic gates: AND gate - output is 1 if BOTH inputs are 1 OR gate - output is 1 if AT LEAST one input is 1 XOR gate - output is 1 if ONLY one input is 1 NAND gate - output is 1 if AT LEAST one input is 0 NOR gate - output is 1 if BOTH inputs are 0 There is a sixth element in digital logic, the inverter (sometimes called a NOT gate). Inverters aren’t truly gates, as they do not make any decisions. The output of an inverter is a 1 if the input is a 0, and vise versa. A few things of note about the above image: Usually, the name of the gate is not printed; the symbol is assumed to be sufficient for identification. The A-B-Q type terminal notation is standard, although logic diagrams will usually omit them for signals which are not inputs or outputs to the system as a whole. Two input devices are standard, but you will occasionally see devices with more than two inputs. They will, however, only have one output. Digital logic circuits are usually represented using these six symbols; inputs are on the left and outputs are to the right. While inputs can be connected together, outputs should never be connected to one another, only to other inputs. One output may be connected to multiple inputs, however. Truth Tables The descriptions above are adequate to describe the functionality of single blocks, but there is a more useful tool available: the truth table. Truth tables are simple plots which explain the output of a circuit in terms of the possible inputs to that circuit. Here are truth tables describing the six main elements: Truth tables can be expanded out to an arbitrary scale, with as many inputs and outputs as you can handle before your brain melts. Here’s what a four-input circuit and truth table look like: Written Boolean Logic It is, of course, useful to be able to write in a simple mathematical format an equation representing a logical operation. To that end, there are mathematical symbols for the unique operations: AND, OR, XOR, and NOT. A AND B should be written as AB (or sometimes A • B) A OR B should be written as A + B A XOR B should be written as A ⊕ B NOT A should be written as A' or A You’ll note that there are two missing elements on that list: NAND and NOR. Typically, those are simply represented by complementing the appropriate representation: A NAND B is written as (AB)' , (A • B)' , or (AB) A NOR B is written as (A + B)' or (A + B) Sequential Logic Combinational logic is great, but without adding sequential circuitry, modern computing would not be possible. Sequential circuitry is what adds memory to our logical systems. As mentioned earlier, combinational logic produces results after a delay. That delay varies according to lots and lots of things: the manufacturing process of the parts involved, the temperature of the silicon, the complexity of the circuit. If the output of a circuit is dependant upon results from two other combinational circuits and the results arrive at different times (which they will, in the real world), a combinational circuit will “glitch” briefly, outputting a result which may not be consistent with the desired operation. A sequential circuit, however, only samples and propagates the output at specific times. If the input changes between those times, it is ignored. The sampling time is usually synchronized across the entire circuit and is referred to as the “clock”. When a computer’s “speed” is cited, this is the value in question. It is possible to design “asynchronous” sequential circuits, which do not rely on a synchronized global clock. However, those systems pose great difficulties, and we won’t be discussing them here. As a side note, any section of digital logic will have two characteristic delay values: the minimum delay time and the maximum delay time. If the circuit fails the minimum delay time (i.e., is faster than it should be), the circuit will fail, irreparably so. If that circuit is part of a larger device, like a computer CPU, the entire device is garbage and cannot be used. If the maximum delay time fails (i.e., the circuit is slower than it should be), the clock speed can be reduced to accommodate the slowest circuit in the system. Maximum delay times tend to go up as the silicon forming a circuit warms up, which is why computers become unstable when they overheat or as the clock speed is increased (as is the case with overclocking). Sequential Circuit Elements As is the case with combinational logic, there are several basic circuit elements which form the building blocks of sequential circuits. These blocks are built up from the basic combinational elements, using feedback from the output to stabilize the input. They come in two “flavors”: latches and flip-flops. While the terms are frequently used interchangeably, latches are generally less useful, as they are not clocked; we’ll focus on flip-flops. D-type Flip-Flop The simplest type of flip-flop is the D-type. D flip-flops are simple – upon a clock edge (normally rising, although they can be found with a built-in inverter to clock in on the falling edge instead), the input is latched to the output. Usually, the clock input is denoted by the small triangle impinging on the symbol. Most flip-flops provide two outputs: the “normal” output, and the complemented output. T-type Flip-Flop Only slightly more complex is the T-type. The ’T' stands for “toggle.” When a clock edge occurs, if the input T is a 1, the output changes state. If the input is a 0, the output remains the same. As with the D-type, the complement of the output is usually provided. A useful function of the T flip-flop is as a clock division circuit. If T is held high, the output will be the clock frequency divided by two. A chain of T flip-flops can thus be used to produce slower clocks from a device’s master clock. JK-type Flip-Flop Finally, we have the JK-type. The JK-type is the only one of the three which truly requires a truth table to explain; it has two inputs (J and K), and the output can be left the same, set, cleared, or toggled, depending on the combination of input signals present. Of course, as with all flip-flops, the input at the moment of the clock is the only thing that matters. Setup, Hold, and Propagation Times All sequential circuits have what are called “setup” and “hold” times, as well as a propagation delay. Understanding these three things is critical to designing sequential circuits that work as expected. The setup time is the minimum amount of time before a rising clock edge occurs that a signal must arrive at the input of a flip-flop in order for the flip-flop to latch the data correctly. Likewise, the hold time is the minimum time a signal must remain stable after the rising clock edge occurs before it can be allowed to change. While setup and hold times are given as minimum values, the propagation delay is given as a maximum. Simply put, the propagation delay is the greatest amount of time after a falling edge at the clock before you can expect to see the signal on the outputs. Here’s a graphic explaining them: Note that in the above image, transitions are drawn as being slightly angled. This serves two purposes: it reminds us that clock and data edges are never truly right angles and will always have some non-zero rise or fall time, and it makes it easier to see where the vertical lines marking the various times intersect with the signals. The combination of these three values determines the highest clock speed a device may use. If the propagation delay of one part plus the setup time of the next part in the circuit exceeds the time between the falling edge of one clock pulse and the rising edge of the next, the data will not be stable on the input of the second component, causing it to behave in an unexpected manner. Metastability Failing to adhere to setup and hold times can lead to a problem called “metastability”. When a circuit is in a metastable state, the output of a flip-flop can oscillate rapidly between the two normal states – often at a rate far above the clock rate of the circuit. Metastability problems can range from spurious operation up to damage of the chip, since they can increase current consumption. While metastability usually resolves on its own, by the time it does so, the system may be in a totally unknown state and need to be completely reset to restore proper operation. A common way in which metastability issues arise is when a signal crosses clock domains – in other words, when a signal passes between devices which are being clocked by different sources. Since the clocks are not synchronized (and even if the clocks are at the same nominal frequency, reality dictates that they will be slightly different), eventually a clock edge and a data edge are bound to be too close for comfort, resulting in a setup time violation. A simple fix for this issue is to run all inputs into a system through a pair of cascaded D flip-flops. Even if the first flip-flop goes into metastability, it will (hopefully) have settled down to a steady state before the next clock pulse, allowing the second flip-flop to read the correct data. This results in a one-cycle delay in incoming data edges, which is almost always insignificant compared to the risk of metastability. Boolean Logic in Programming All of this can be applied in the programming world, as well. Most programs are simply decision trees: “if this is true, then do this”. To explain this, we’ll use C-code in an Arduino context. Bitwise Logic When we talk about “bitwise” logic, what we really mean is logical operations which return a value. Take, for example, this piece of code: byte a = b01010101; byte b = b10101010; byte c; We can do a bitwise operation using ‘a’ and ‘b’ and putting the result into ‘c’. Here’s what that looks like: c = a & b; // bitwise AND-ing of a and b; the result is b00000000 c = a | b; // bitwise OR-ing of a and b; the result is b11111111 c = a ^ b; // bitwise XOR-ing of a and b; the result is b11111111 c = ~a; // bitwise complement of a; the result is b10101010 In other words, the each bit in the result is equal to the operation applied to the two corresponding bits in the operands: Okay, that’s great, but what of it? It turns out we can do some pretty useful things by using bitwise operators to manipulate registers: we can selectively clear, set, or toggle single bits, check to see if a bit is set or clear, or if several bits are set or clear. Here are some examples using these operations: c = b00001111 & a; // clear the high nibble of a, but leave the low nibble alone. // the result is b00000101. c = b11110000 | a; // set the high nibble of a, but leave the low nibble alone. // the result is b11110101. c = b11110000 ^ a; // toggle all the bits in the high nibble of a. // the result is b10100101. Any bitwise operation can be self-applied by combining it with the equal sign: a ^= b11110000; // XOR a with b11110000 and store the result back in a b |= b00111100; // OR b with b00111100 and store the result back in b Bit Shifting Another useful bitwise operation that can be performed on a piece of data is a bit shift. This is simply a slide of the data left or right by a certain number of places; data which is shifted out disappears and is replaced by a 0 being shifted in from the other end. byte d = b11010110; byte e = d>>2; // right-shift d by two positions; e = b00110101 e = e<<3; // left-shift e by three positions; e = b10101000 We’ll demonstrate some uses of bit shifting later. One very useful application for bit shifts is multiplication and division: each right shift is the same as a division by two (although remainder information is lost) and each left shift is the same as a multiplication by two. This is useful because multiply and divide are often very time expensive operations on small processors, like the Arduino’s, but bit shifts are usually very efficient. Comparison and Relational Operators We’ll want some way to compare two values: there is a family of operators which do just that and return “TRUE” or “FALSE” depending on the result of the comparison. == “is equal to” (true if values are equal, false otherwise) != “is not equal to” (true if values are different) > “is greater than” (true if left operand is greater than right operand) < “is less than” (true if left operand is less than right operand) >= “is greater than, or equal to” (true if left operand is greater than, or exactly equal to, right operand) <= “is less than, or equal to” (true if left operand is less than, or exactly equal to, right operand) It is generally quite important that the values compared be of the same data type; unexpected things can happen if you compare a “byte” and an “int”, for example. Logical Operators Logical operators are operators which produce a “TRUE” or “FALSE”, rather than a new value of the same type. They’re more like what we tend to think of as conjunctions: “If it’s not raining, and it’s windy, go fly a kite”. Translated into C, that sentence might look like this: if ( (raining != true) && (windy == true) ) flyKite(); Note the parentheses around the two subclauses. Though not strictly necessary, it’s good practice to keep your code as readable as possible by grouping subclauses together. Also note that the logical AND operator (&&) produces a true/false answer based on whether or not the subclauses produced true/false answers. We could just as easily have had a numeric value in one of the subclauses: if ( (raining != true) && ( (windSpeed >= 5) || (reallyBusy != true) ) ) flyKite(); This clause will send me out to fly a kite, so long as it’s not raining, but only if there’s some wind or I’m not busy (I will try and fly with no wind). Again, note the parentheses. If we remove the parentheses around “(windSpeed >= 5) || (reallyBusy != true)” – with || representing the OR operator – we create an ambiguous statement which may or may not do what we want it to do. Flow Control Now that we can create complex logical statements, let’s look at the things we can do with the answers to those questions. if/else if/else Statements The simplest decision is “if/else”. If/else if/else allow you to set up a series of tests, of which only one can ever be executed at any time: if ( reallyBusy == true ) workHarder(); else if ( (raining != true) && (windy == true) ) flyKite(); else work(); With those three statements, I’ll never fly a kite if I’m really busy, and if I’m not really busy, and it’s not a good day for it, I’ll just keep working. Let’s change the else if() to if(), like so: if ( reallyBusy == true ) workHarder(); if ( (raining != true) && (windy == true) ) flyKite(); else work(); Now, if we’ve got a nice kite flying day on our hands, even if I’m really busy, I’ll only work harder for a very, very short period–basically, right up until I notice that it’s nice out. Furthermore, if it’s not a nice day, my work harder status will be downgraded to just plain old work immediately after I start working harder! You can imagine what would happen if we replaced “workHarder()” with “turnLEDOn()” and “work()” with “turnLEDOff()”. In the first case, the LED may be on for some time, or off for some time. In the second case, however, regardless of the state of the “reallyBusy” flag, the LED will turn off almost instantly after the first if() statement turned it on, and you’d find yourself sitting around wondering why the “reallyBusy” light never turns on! switch/case/default Statements Less powerful but more readable than a long chain of if/else statements, switch/case/default allows you to make a decision based on the value of a variable: switch(menuSelection) { case '1': doMenuOne(); break; case '2': doMenuTwo(); break; case '3': doMenuThree(); break; default: flyKite(); break; } The switch() statement only allows us to check equivalence, but since that’s a fairly common thing to want to do, it comes in pretty handy. There are two really important things to notice about this: the “break;” statements and the “default:” case. “default:” is what will be executed if none of the others match. It’s not strictly necessary; if there’s no default case, than nothing happens if all the matches fail. Of course, you usually want something to happen, and it’s best not to assume that it’s impossible for all matches to fail. “break;” jumps out of the current conditional. It can be used inside of any type of conditional (more on that later), and in this case, a failure to include a break at the end of each case will result in code after the case being executed, even if subsequent case matches fail. while/do…while Loops So far, we’ve looked at code for making a decision once. What if you want to repeat an action, over and over, as long as a condition holds? That’s where while() and do…while() come into play. while (windy == true) flyKite(); When your code reaches a while() statement, the program evaluates the conditional (“Is it windy?”) and, if it evaluates to “TRUE”, executes the code. Once code execution is complete, the conditional will be evaluated once more. If the conditional is still “TRUE”, the code will execute again. This repeats over and over, until the conditional evaluates to “FALSE” or a break statement is encountered. You can nest an if() statement (or a switch(), or another while(), or in fact anything you want) inside your while() loop: while (windy == true) { flyKite(); if (bossIsMad == true) break; } So, with that loop, I’ll fly my kite until the wind gives out or my boss gets mad at me. A variation on while() loops is the do…while() loop. do { flyKite(); } while (windy == true); In this case, the code inside the brackets runs once, even if the conditional is false. In other words, regardless of the state of the wind, I’ll go out and drag a kite around, but if the wind isn’t there, I’ll give up. Finally, by sticking “TRUE” into the conditional, it’s possible to create code that will execute forever: while(true) { flyKite(); } With that chunk of code, I’ll just keep dragging my kite around the field forever, regardless of wind, my boss’s satisfaction with it, hunger, cougars, etc. It’s still possible to break out of that code using the break statement, of course; it will just never cease execution on its own. for() Loops The last type of conditional execution we need to consider is the for() loop. for() loops allow us to execute a chunk of code a specific number of times. The syntax of a for loop looks like this: for (byte i = 0; i < 10; i++) { Serial.print("Hello, world!"); } Within the for() loop parentheses are three semicolon separated statements. The first one is the iterator: the variable which we are changing with each pass. It’s also where the iterator’s initial value is set. The center one is the comparison we’ll do after each pass. Once that comparison fails, we break out of the loop. The last statement is what we want to do after each pass through the loop. In this case, we want to increment the iterator by one. The most common error in a for() loop is an off-by-one error: you mean for the code to execute 10 times, but it ends up executing 9 times, or 11 times. This is usually a result of using a “<=” instead of “<” or vice versa.

Analog Signals Define: Signals Before going too much further, we should talk a bit about what a signal actually is, electronic signals specifically (as opposed to traffic signals, albums by the ultimate power-trio, or a general means for communication). The signals we’re talking about are time-varying “quantities” which convey some sort of information. In electrical engineering the quantitythat’s time-varying is usually voltage (if not that, then usually current). So when we talk about signals, just think of them as a voltage that’s changing over time. Signals are passed between devices in order to send and receive information, which might be video, audio, or some sort of encoded data. Usually the signals are transmitted through wires, but they could also pass through the air via radio frequency (RF) waves. Audio signals, for example might be transferred between your computer’s audio card and speakers, while data signals might be passed through the air between a tablet and a WiFi router. Analog Signal Graphs Because a signal varies over time, it’s helpful to plot it on a graph where time is plotted on the horizontal, x-axis, and voltage on the vertical, y-axis. Looking at a graph of a signal is usually the easiest way to identify if it’s analog or digital; a time-versus-voltage graph of an analog signal should be smooth and continuous. While these signals may be limited to a range of maximum and minimum values, there are still an infinite number of possible values within that range. For example, the analog voltage coming out of your wall socket might be clamped between -120V and +120V, but, as you increase the resolution more and more, you discover an infinite number of values that the signal can actually be (like 64.4V, 64.42V, 64.424V, and infinite, increasingly precise values). Example Analog Signals Video and audio transmissions are often transferred or recorded using analog signals. The composite video coming out of an old RCA jack, for example, is a coded analog signal usually ranging between 0 and 1.073V. Tiny changes in the signal have a huge effect on the color or location of the video. An analog signal representing one line of composite video data. Pure audio signals are also analog. The signal that comes out of a microphone is full of analog frequencies and harmonics, which combine to make beautiful music. Digital Signals Digital signals must have a finite set of possible values. The number of values in the set can be anywhere between two and a-very-large-number-that’s-not-infinity. Most commonly digital signals will be one of two values – like either 0V or 5V. Timing graphs of these signals look like square waves. Or a digital signal might be a discrete representation of an analog waveform. Viewed from afar, the wave function below may seem smooth and analog, but when you look closely there are tiny discrete steps as the signal tries to approximate values: That’s the big difference between analog and digital waves. Analog waves are smooth and continuous, digital waves are stepping, square, and discrete. Example Digital Signals Not all audio and video signals are analog. Standardized signals like HDMI for video (and audio) and MIDI, I2S, or AC'97for audio are all digitally transmitted. Most communication between integrated circuits is digital. Interfaces like serial, I2C, and SPI all transmit data via a coded sequence of square waves. Serial peripheral interface (SPI) uses many digital signals to transmit data between devices. Analog and Digital Circuits Analog Electronics Most of the fundamental electronic components – resistors, capacitors, inductors, diodes, transistors, and operational amplifiers – are all inherently analog. Circuits built with a combination of solely these components are usually analog. Analog circuits are usually complex combinations of op amps, resistors, caps, and other foundational electronic components. This is an example of a class B analog audio amplifier. Analog circuits can be very elegant designs with many components, or they can be very simple, like two resistors combining to make a voltage divider. In general, though, analog circuits are much more difficult to design than those which accomplish the same task digitally. It takes a special kind of analog circuit wizard to design an analog radio receiver, or an analog battery charger; digital components exist to make those designs much simpler. Analog circuits are usually much more susceptible to noise (small, undesired variations in voltage). Small changes in the voltage level of an analog signal may produce significant errors when being processed. Digital Electronics Digital circuits operate using digital, discrete signals. These circuits are usually made of a combination of transistors and logic gates and, at higher levels, microcontrollers or other computing chips. Most processors, whether they’re big beefy processors in your computer, or tiny little microcontrollers, operate in the digital realm. Digital circuits make use of components like logic gates, or more complicated digital ICs (usually represented by rectangles with labeled pins extending from them). Digital circuits usually use a binary scheme for digital signaling. These systems assign two different voltages as two different logic levels – a high voltage (usually 5V, 3.3V, or 1.8V) represents one value and a low voltage (usually 0V) represents the other. Although digital circuits are generally easier to design, they do tend to be a bit more expensive than an equally tasked analog circuit. Analog and Digital Combined It’s not rare to see a mixture of analog and digital components in a circuit. Although microcontrollers are usually digital beasts, they often have internal circuitry which enables them to interface with analog circuitry (analog-to-digital converters, pulse-width modulation, and digital-to-analog converters. An analog-to-digital converter (ADC) allows a microcontroller to connect to an analog sensor (like photocells or temperature sensors), to read in an analog voltage. The less common digital-to-analog converter allows a microcontroller to produce analog voltages, which is handy when it needs to make sound.

Datasheets are instruction manuals for electronic components. They (hopefully) explain exactly what a component does and how to use it. Unfortunately these documents are usually written by engineers for other engineers, and as such they can often be difficult to read, especially for newcomers. Nevertheless, datasheets are still the best place to find the details you need to design a circuit or get one working. A datasheet’s contents will vary widely depending on the type of part, but they will usually have most of the following sections: The first page is usually a summary of the part’s function and features. This is where you can quickly find a description of the part's functionality, the basic specifications(numbers that describe what a part needs and can do), and sometimes a functional block diagram that shows the internal functions of the part. This page will often give you a good first impression as to whether potential part will work for your project or not: A pinout lists the part’s pins, their functions, and where they’re physically located on the part for various packages the part might be available in. Note the special marks on the part for determining where pin 1 is (this is important when you plug the part into your circuit!), and how the pins are numbered (the below parts are numbered counterclockwise). You'll find some acronyms here: VCC is the supply voltage (commonly 5V or 3.3V), CLK is clock, CLR is clear, OE is output enable, etc. These acronyms should be spelled out later in the datasheet, but if not, try Google or Wikipedia. If a pin has a star next to it or a line over the name, that's an indication that the pin is active low which means that you'll pull the pin low (0V) to activate it, rather than H (VCC): Detailed tables of electrical specifications follow. These will often list the absolute maximum ratings a part can withstand before being damaged. Never exceed these or you'll be replacing a possibly expensive part! You'll also see the more normal recommended operating conditions. These may include voltage and current ranges for various functions, timing information, temperature ranges, bus addresses, and other useful performance information. The below excerpt contains a good example where the fine print can help you out: "Note 3" in this set of specifications states that "All unused inputs of the device must be held at VCC or GND to ensure proper device operation." This is a reminder to tie all unused inputs H or L to prevent them from "floating" between H and L which can make your circuit malfunction and be difficult to debug: Some parts will have one or more graphs showing the part’s performance vs. various criteria (supply voltage, temperature, etc.) Keep an eye out for "safe zones" where reliable operation is guaranteed: Truth tables show how changing the inputs to a part will affect its output. Each line has all the part's inputs set to specific states, and the resulting output of the part. "H" means that input is a logical high (usually VCC), "L" means a logical low (usually GND), "X" means the chip doesn't care what the input is (could be H or L), and an arrow means that that you should change the state of that pin from L to H or H to L depending on the arrow direction. This is called "clocking" an input, and many chips rely on this for proper operation: Timing diagrams show how data should be sent to and received from the part, and what speed it should be sent / received. These are typically laid out with various inputs and outputs as horizontal lines, showing the logic transitions that happen to those lines over time. If the trace dips down, that's a L input or output. If the line rises higher, that's a H input our output. Timing specifications are laid out as arrows between transitions (names are referenced back to timing numbers in the electrical specs), and vertical bars or arrows will link related transitions: Complex parts will have extensive application information. This varies depending on the part, but may include detailed descriptions of pin functions, how to communicate with the part, lists of commands, memory tables, etc. This is often very useful information, so read through it carefully: Some datasheets will include example schematics for various circuits that can be built around the part. These are often very useful building blocks for interesting projects, so be sure to look through them: Some parts are sensitive to the way they’re built into a circuit, and the datasheet will provide layout considerations. These can range from noise-reduction techniques, to dealing with thermal issues, to mechanical mounting considerations as with the accelerometer below. This all tends to be very good advice, that if followed from the start will lead to the most trouble-free circuits. Likewise, if you don't follow this advice, your circuit may have problems later on that can be hard to diagnose, and harder to fix: At the end of many datasheets is packaging information, which provides accurate dimensions of the packages a part is available in. Finally, a few of our customers have correctly pointed out that datasheets are subject to having errors just like anything else, and running into one of these errors can be frustrating to say the least. To reduce this possibility, be sure you have the latest version of a datasheet before doing any serious work. These are available at the manufacturer's website, which are updates and corrections to a part's specifications often found after the part went to production. And if nothing else helps, many manufacturers have applications engineers you can contact to get help on hard-to-solve problems. When working with a new part for the first time, or when deciding which part to use for your project, it’s a very good idea to read that part’s datasheet from beginning to end, paying close attention to the fine print. You’ll often come up with a bit of knowledge or a shortcut that will save you hours of grief later on