General Electronics Articles

Article / Updated 06-26-2024

Capacitors are among the most useful of all electronic components. And capacitance is the term that refers to the ability of a capacitor to store charge. It's also the measurement used to indicate how much energy a particular capacitor can store. The more capacitance a capacitor has, the more charge it can store. Capacitance is measured in units called farads (abbreviated F). The definition of one farad is deceptively simple. A one-farad capacitor holds a voltage across the plates of exactly one volt when it's charged with exactly one ampere per second of current. Note that in this definition, the "one ampere per second of current" part is really referring to the amount of charge present in the capacitor. There's no rule that says the current has to flow for a full second. It could be one ampere for one second, or two amperes for half a second, or half an ampere for two seconds. Or it could be 100 mA for 10 seconds or 10 mA for 100 seconds. One ampere per second corresponds to the standard unit for measuring electric charge, called the coulomb. So another way of stating the value of one farad is to say that it's the amount of capacitance that can store one coulomb with a voltage of one volt across the plates. It turns out that one farad is a huge amount of capacitance, simply because one coulomb is a very large amount of charge. To put it into perspective, the total charge contained in an average lightning bolt is about five coulombs, and you need only five, one-farad capacitors to store the charge contained in a lightning strike. (Some lightning strikes are much more powerful, as much as 350 coulombs.) It's a given that Doc Brown's flux capacitor was in the farad range because Doc charged it with a lightning strike. But the capacitors used in electronics are charged from much more modest sources. Much more modest. In fact, the largest capacitors you're likely to use have capacitance that is measured in millionths of a farad, called microfarads and abbreviated μF. And the smaller ones are measured in millionths of a microfarad, also called a picofarad and abbreviated pF. Here are a few other things you should know about capacitor measurements: Like resistors, capacitors aren't manufactured to perfection. Instead, most capacitors have a margin of error, also called tolerance. In some cases, the margin of error may be as much as 80%. Fortunately, that degree of impression rarely has a noticeable effect on most circuits. The μ in μF isn't an italic letter u; it's the Greek letter mu, which is a common abbreviation for micro. It's common to represent values of 1,000 pF or more in μF rather than pF. For example, 1,000 pF is written as 0.001 μF, and 22,000 pF is written as 0.022 μF.

Article / Updated 09-13-2023

Before you can fire up your Raspberry Pi and start building your own electronics projects, you need to do some basic setup work. Start by setting up the hardware. You'll need the following to set up your Pi so that you can program it for your projects: A Raspberry Pi 2 or 3. A suitable power supply: The Raspberry Pi requires a 5 V power supply connected via a micro-USB connection on the card. The Pi itself will draw about 800 mA, so be sure to use a power supply that can handle at least that much current draw. A monitor: You don't need a large monitor, but go for at least 17 inches. An HDMI cable: If your monitor has an HDMI connection, you'll need a cable with HDMI connectors on both ends. If your monitor has some other type of connection, such as DVI or VGA, you'll need an adapter to connect your monitor to the Pi's HDMI connector. A USB keyboard: Any keyboard with a USB connector will do. A USB mouse: Any mouse with a USB connector will do. A microSD card with NOOBS: The Raspberry Pi uses a microSD card instead of a disk drive. Ideally, you should purchase a microSD card that already has a special program called NOOBS installed on it. (NOOBS stands for New Out Of the Box Software.) This program will allow you to install an operating system so that your Pi can run. If you prefer, you can format your own microSD card for your Pi. You can do that by downloading NOOBS from Raspberry Pi — Teach, Learn, and Make with Raspberry Pi on your computer and then copying the NOOBS software to the microSD card. A network connection: A network connection is essential to download several of the support packages you'll need for your projects. You can connect your Pi to a network in one of two ways: If you have a Raspberry Pi 3, you can use the built-in Wi-Fi to connect to a wireless network. You can use a standard Ethernet cable to plug a Raspberry Pi 2 or 3 into a wired network, provided you have a nearby router or switch with an available network port. That's all you need to get started. Plug the monitor, mouse, and keyboard into your Pi's HDMI and USB ports, insert the microSD card into the microSD slot, and then plug in the power connector. Your Pi will start right up.

Article / Updated 09-11-2023

All of electronics can be divided into two broad categories: analog and digital. One of the most common examples of the difference between analog and digital devices is a clock. On the analog clock, the time is represented by hands that spin around a dial and point to a location on the dial that represents the approximate time. On a digital clock, a numeric display indicates the exact time. Analog refers to circuits in which quantities such as voltage or current vary at a continuous rate. When you turn the dial of a potentiometer, for example, you change the resistance by a continuously varying rate. The resistance of the potentiometer can be any value between the minimum and maximum allowed by the pot. If you create a voltage divider by placing a fixed resistor in series with a potentiometer, the voltage at the point between the fixed resistor and the potentiometer increases or decreases smoothly as you turn the knob on the potentiometer. In digital electronics, quantities are counted rather than measured. There’s an important distinction between counting and measuring. When you count something, you get an exact result. When you measure something, you get an approximate result. Consider a cake recipe that calls for 2 cups of flour, 1 cup of milk, and 2 eggs. To get 2 cups of flour, you scoop some flour into a 1-cup measuring cup, pour the flour into the bowl, and then do it again. To get a cup of milk, you pour milk into a liquid measuring cup until the top of the milk lines up with the 1-cup line printed on the measuring cup and then pour the milk into the mixing bowl. To get 2 eggs, you count out 2 eggs, crack them open, and add them to the mixing bowl. The measurements for flour and milk in this recipe are approximate. A teaspoon too much or too little won’t affect the outcome. But the eggs are precisely counted: exactly 2. Not 3, not 1, not 11/2, but 2. You can’t have a teaspoon too many or too few eggs. There will be exactly 2 eggs, because you count them. So which is more accurate — analog or digital? In one sense, digital circuits are more accurate because they count with complete precision. You can precisely count the number of jelly beans in a jar, for example. But if you weigh the jar by putting it on an analog scale, your reading may be a bit imprecise because you can’t always judge the exact position of the needle. Say that the needle on the scale is about halfway between 4 pounds and 5 pounds. Does the jar weigh 4.5 pounds or 4.6 pounds? You can’t tell for sure, so you settle for approximately 4.5 pounds. On the other hand, digital circuits are inherently limited in their precision because they must count in fixed units. Most digital thermometers, for example, have only one digit to the right of the decimal point. Thus, they can indicate a temperature of 98.6 or 98.7 but can’t indicate 98.65. Here are a few other thoughts to ponder concerning the differences between digital and analog systems: Saying that a system is digital isn’t the same as saying that it’s binary. Binary is a particular type of digital system in which the counting is all done with the binary number system. Nearly all digital systems are also binary systems, but the two words aren’t interchangeable. Many systems are a combination of binary and analog systems. In a system that combines binary and analog values, special circuitry is required to convert from analog to digital, or vice versa. An input voltage (analog) might be converted to a sequence of pulses, one for each volt; then the pulses can be counted to determine the voltage.

Article / Updated 03-01-2023

A Raspberry Pi (sometimes just called a Pi for short) is a very small computer. Raspberry Pi is a popular alternative to Arduino, BASIC Stamp, and other types of microcontrollers and is the ideal computer for people who love to make their own gadgets. Physically, a Raspberry Pi resembles an Arduino or a BASIC Stamp. However, the Raspberry Pi is much more than a microcontroller; it is a full-blown computer system, implemented on a single small card. In fact, a Raspberry Pi has most of the features commonly found on a desktop or laptop computer. Yet, besides its small size, a Raspberry Pi has other features not commonly found on a desktop, such as the ability to directly control digital I/O pins. Thus, you can use a Raspberry Pi with external devices such as LEDs, push buttons, potentiometers, various types of sensors, and servo or stepper motors. It contains most of the components found in a traditional desktop computer, but all squeezed onto a small board about the size of a deck of playing cards. The newest version of the Raspberry Pi, called the Raspberry Pi 3, is pictured here. This version of the Raspberry Pi includes all of the following packed onto the board: CPU: A quad-core 64-bit ARM Corex-A53 microprocessor running at 1.2GHz. RAM: 1GB. USB ports: Four standard-size USB 2.0 ports mounted on the board. These ports can be used to connect any USB device, including a keyboard, a mouse, or a flash drive. Video: A built-in graphics processor that can support 1080p resolution (1920 x 1080). HDMI: A full-size HDMI connector is mounted on the board to connect a video monitor. Display serial interface (DSI): A display interface designed to connect to small LCDs via a 15-pin ribbon cable. MicroSDHC card: The MicroSDHC card acts as the computer's disk drive. The operating system (Linux) is installed on the MicroSD card, along with any other software you want to use. Ethernet networking: A built-in RJ-45 connector for networking. 802.11n wireless network: A built-in wireless network connection. The antenna is actually built into the board itself, so no external antenna is needed. Bluetooth: Built-in Bluetooth networking for wireless devices such as a keyboard, a mouse, and headphones. Camera serial interface (CSI): A special interface designed to connect to a camera device via a 15-pin ribbon cable. Audio: A 3.5mm audio jack for sound applications. Power: The Raspberry Pi is powered by a 5 V supply connected to the board via a micro-USB connection, the same type used by most smartphone rechargers. GPIO header: The most interesting thing about the Raspberry Pi from an electronic enthusiast's perspective is the 40-pin GPIO header, which provides access to a variety of features, including 26 general-purpose input-output (GPIO) pins. These pins work the same as the digital I/O pins found on Arduino and BASIC Stamp microprocessors, and can be accessed via programs that you write for the Raspberry Pi. You can use these GPIO pins as output pins to connect to devices such as LEDs, servo or stepper motors, and so on. Or, you can use them as input pins to read input from external switches, potentiometers, or other types of sensors. Unlike the digital I/O pins found on Arduino or BASIC Stamp microprocessors, the Raspberry Pi GPIO pins work at a voltage level of 3.3 V rather than 5 V to indicate HIGH signals. You'll need to adjust your circuits accordingly to deal with the smaller input and output voltage levels. In particular, if you apply a 5 V input to GPIO input pin, you run the risk of damaging your Raspberry Pi.

Cheat Sheet / Updated 02-02-2023

As you design and build with electronic circuits, you’ll invariably find yourself scratching your head trying to remember what color stripes are on a 470 Ω resistor or what pin on a 555 timer integrated circuit (IC) is the trigger input. Never fear! This handy Cheat Sheet will help you remember such mundane details so you can get on with the fun stuff.

Cheat Sheet / Updated 02-02-2023

Electronics is more than just schematics and circuits. By using various components, such as resistors and capacitors, electronics allows you to bend electric current to your will to create an infinite variety of gizmos and gadgets. In exploring electronics, use this handy reference for working with Ohm’s, Joule’s, and Kirchhoff’s Laws; making important calculations; determining the values of resistors and capacitors according to the codes that appear on their casings; and using a 555 timer and other integrated circuits (ICs).

Article / Updated 09-17-2021

You need a closed path, or closed circuit, to get electric current to flow. If there's a break anywhere in the path, you have an open circuit, and the current stops flowing — and the metal atoms in the wire quickly settle down to a peaceful, electrically neutral existence. A closed circuit allows current to flow, but an open circuit leaves electrons stranded. Picture a gallon of water flowing through an open pipe. The water will flow for a short time but then stop when all the water exits the pipe. If you pump water through a closed pipe system, the water will continue to flow as long as you keep forcing it to move. Open circuits by design Open circuits are often created by design. For instance, a simple light switch opens and closes the circuit that connects a light to a power source. When you build a circuit, it's a good idea to disconnect the battery or other power source when the circuit is not in use. Technically, that's creating an open circuit. A flashlight that is off is an open circuit. In the flashlight shown here, the flat black button in the lower left controls the switch inside. The switch is nothing more than two flexible pieces of metal in close proximity to each other. With the black button slid all the way to the right, the switch is in an open position and the flashlight is off. A switch in the open position disconnects the light bulb from the battery, creating an open circuit. Turning the flashlight on by sliding the black button to the left pushes the two pieces of metal together — or closes the switch — and completes the circuit so that current can flow. Closing the switch completes the conductive path in this flashlight, allowing electrons to flow. Open circuits by accident Sometimes open circuits are created by accident. You forget to connect a battery, for instance, or there's a break in a wire somewhere in your circuit. When you build a circuit using a solderless breadboard, you may mistakenly plug one side of a component into the wrong hole in the breadboard, leaving that component unconnected and creating an open circuit. Accidental open circuits are usually harmless but can be the source of much frustration when you're trying to figure out why your circuit isn't working the way you think it should. Short circuits take the wrong path Short circuits are another matter entirely. A short circuit is a direct connection between two points in a circuit that aren't supposed to be directly connected, such as the two terminals of a power supply. Electric current takes the path of least resistance, so in a short circuit, the current will bypass other parallel paths and travel through the direct connection. (Think of the current as being lazy and taking the path through which it doesn't have to do much work.) In a short circuit, current may be diverted from the path you intended it to flow through. If you short out a power supply, you send large amounts of electrical energy from one side of the power supply to the other. With nothing in the circuit to limit the current and absorb the electrical energy, heat builds up quickly in the wire and in the power supply. A short circuit can melt the insulation around a wire and may cause a fire, an explosion, or a release of harmful chemicals from certain power supplies, such as a rechargeable battery or a car battery.

Article / Updated 09-17-2021

Semiconductors are used extensively in electronic circuits. As its name implies, a semiconductor is a material that conducts current, but only partly. The conductivity of a semiconductor is somewhere between that of an insulator, which has almost no conductivity, and a conductor, which has almost full conductivity. Most semiconductors are crystals made of certain materials, most commonly silicon. To understand how semiconductors work, you must first understand a little about how electrons are organized in an atom. The electrons in an atom are organized in layers. These layers are called shells. The outermost shell is called the valence shell. The electrons in this shell are the ones that form bonds with neighboring atoms. Such bonds are called covalent bonds. Most conductors have just one electron in the valence shell. Semiconductors, on the other hand, typically have four electrons in their valence shell. Semiconductors are made of crystals If all the neighboring atoms are of the same type, it's possible for all the valence electrons to bind with valence electrons from other atoms. When that happens, the atoms arrange themselves into structures called crystals. Semiconductors are made out of such crystals, usually silicon crystals. Here, each circle represents a silicon atom, and the lines between the atoms represent the shared electrons. Each of the four valence electrons in each silicon atom is shared with one neighboring silicon atom. Thus, each silicon atom is bonded with four other silicon atoms. Pure silicon crystals are not all that useful electronically. But if you introduce small amounts of other elements into a crystal, the crystal starts to conduct in an interesting way. Two types of conductors The process of deliberately introducing other elements into a crystal is called doping. The element introduced by doping is called a dopant. By carefully controlling the doping process and the dopants that are used, silicon crystals can transform into one of two distinct types of conductors: N-type semiconductor: Created when the dopant is an element that has five electrons in its valence layer. Phosphorus is commonly used for this purpose. The phosphorus atoms join right in the crystal structure of the silicon, each one bonding with four adjacent silicon atoms just like a silicon atom would. Because the phosphorus atom has five electrons in its valence shell, but only four of them are bonded to adjacent atoms, the fifth valence electron is left hanging out with nothing to bond to. The extra valence electrons in the phosphorous atoms start to behave like the single valence electrons in a regular conductor such as copper. They are free to move about. Because this type of semiconductor has extra electrons, it's called an N-type semiconductor. P-type semiconductor: Happens when the dopant (such as boron) has only three electrons in the valence shell. When a small amount is incorporated into the crystal, the atom is able to bond with four silicon atoms, but since it has only three electrons to offer, a hole is created. The hole behaves like a positive charge, so semiconductors doped in this way are called P-type semiconductors. Like a positive charge, holes attract electrons. But when an electron moves into a hole, the electron leaves a new hole at its previous location. Thus, in a P-type semiconductor, holes are constantly moving around within the crystal as electrons constantly try to fill them up. When voltage is applied to either an N-type or a P-type semiconductor, current flows, for the same reason that it flows in a regular conductor: The negative side of the voltage pushes electrons, and the positive side pulls them. The result is that the random electron and hole movement that's always present in a semiconductor becomes organized in one direction, creating measurable electric current.

Article / Updated 06-18-2020

The figure shows the front and back of one type of mini-speaker. Speakers usually come with leads attached. The leads are twisted together to keep things neat and tidy. You attach the leads to components in your circuit so that electrical current passes from your circuit into the speaker. The speaker then converts the current into sound. A typical speaker contains two magnets and a cone made of paper or plastic (see the following figure). The black material you see in the mini-speaker shown is the paper cone. One of the speaker's magnets is a permanent magnet (meaning that it is always magnetized) and the other is an electromagnet. An electromagnet is just a coil of wire wrapped around a hunk of iron. If no current passes through the coil of wire, the electromagnet is not magnetized. When current passes through the coil of wire, the electromagnet becomes magnetized and gets pulled and then pushed away from the permanent magnet. The cone is attached to the electromagnet, so when the electromagnet moves, the cone vibrates, creating sound (which is just moving air). If you look closely at the back of the speaker, right, you might be able to see that one side of each lead wire is sticking through the back of the black cone. Those wires are connected to the coil inside the speaker. By connecting the other side of the lead wires to your circuit, you control the flow of current through the coil. Depending on what your circuit is doing, current may or may not flow through the coil, and you may or may not hear sound coming from the speaker.

Article / Updated 09-14-2017

Have you ever mixed vinegar with baking soda to create a volcano for a science fair project? The bubbling that you see is the result of a chemical reaction. This reaction is very similar to how batteries work. The reaction, however, occurs inside a battery, hidden from view by the battery case. This reaction is what creates the electrical energy that the battery supplies to circuits. A typical battery, such as a AA or C battery has a case or container. Molded to the inside of the case is a cathode mix, which is ground manganese dioxide and conductors carrying a naturally-occurring electrical charge. A separator comes next. This paper keeps the cathode from coming into contact with the anode, which carries the negative charge. The anode and the electrolyte (potassium hydroxide) are inside each battery. A pin, typically made of brass, forms the negative current collector and is in the center of the battery case. Each battery has a cell that contains three components: two electrodes and an electrolyte between them. The electrolyte is a potassium hydroxide solution in water. The electrolyte is the medium for the movement of ions within the cell and carries the iconic current inside the battery. The positive and negative terminals of a battery are connected to two different types of metal plates, known as electrodes, which are immersed in chemicals inside the battery. The chemicals react with the metals, causing excess electrons to build up on the negative electrode (the metal plate connected to the negative battery terminal) and producing a shortage of electrons on the positive electrode (the metal plate connected to the positive battery terminal). Flashlight or smaller batteries, usually labeled A, AA, C, or D have the terminals built into the ends of the batteries. That's why the battery compartment of your flashlight has a + and a - sign, making it easier for you to install your batteries the correct direction. Larger batteries, like those in a car, have terminals that extend out from the battery. (They generally look like large screw tops.) The difference in the number of electrons between the positive and negative terminals creates the force known as voltage. This force wants to even out the teams, so to speak, by pushing the excess electrons from the negative electrode to the positive electrode. But the chemicals inside the battery act like a roadblock and prevent the electrons from traveling between the electrodes. If there's an alternate path that allows the electrons to travel freely from the negative electrode to the positive electrode, the force (voltage) will succeed in pushing the electrons along that path. When you connect a battery to a circuit, you provide that alternate path for the electrons to follow. So the excess electrons flow out of the battery via the negative terminal, through the circuit, and back into the battery via the positive terminal. That flow of electrons is the electric current that delivers energy to your circuit. When the electrodes are connected via a circuit, for example, the terminals inside a flashlight or those in your vehicle, the chemicals in the electrolyte start reacting. As electrons flow through a circuit, the chemicals inside the battery continue to react with the metals, excess electrons keep building up on the negative electrode, and electrons keep flowing to try to even things up — as long as there's a complete path for the current. If you keep the battery connected in a circuit for a long time, eventually all the chemicals inside the battery are used up and the battery dies (it no longer supplies electrical energy). The electrolyte oxides the anode's powered zinc. The cathode's manganese dioxide/carbon mix reacts with the oxidized zinc to produce electricity. Interaction between the zinc and the electrolyte produces gradually slow the cell's action and lowers its voltage. The collector is a brass pin in the middle of the cell that conducts electricity to the outside circuit. Note that the two electrodes in every battery are made from two different materials, both of which must be electrical conductors. One of the materials gives electrons and the other receives them, which makes the current flow.