General Electronics Articles

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.

Article / Updated 05-09-2017

After you have gathered all the materials you'll need to build a color organ, you're ready to assemble the project. See What You Need to Build a Color Organ Circuit. You'll need the following tools: Soldering iron, preferably with both 20 and 40 W settings Solder Use thicker solder for the line-voltage wires and thin solder for assembling the MK110 kit. Magnifying goggles Phillips screwdriver Small flat-edge jewelers screwdriver Wire cutters Wire strippers Pliers Hobby vise Drill with 1/8-inch, 5/32-inch, 1/4-inch, 5/16-inch, 3/8-inch, and 3/4-inch bits Here are the steps for constructing a color organ: Assemble the Velleman MK110 kit. The kit comes with simple but accurate instructions. Basically, you just mount and solder all the components onto the circuit board. Pay special attention to the color codes for the resistors and the orientation of the diode. It's best to mount the circuit board in a good hobby vise and use an alligator clip or masking tape to hold the components in place while soldering. Drill all the mounting holes in the project box except the hole for the sensitivity control on the left side of the box. The figure shows the orientation of the approximate location of the mounting holes. Use the assembled circuit board to determine the exact drilling locations for the four holes that will mount the circuit board. The position of the other holes isn't critical, with the exception of the hole for the potentiometer knob. Don't drill that hole until Step 4. Mount the four standoffs in the four MK110 circuit board mounting holes. Use four of the machine screws that came with the standoffs. Drill the hole for the circuit board's potentiometer. Set the circuit board on top of the four standoffs to determine the exact location for this hole. Insert the two rubber grommets into the two 3/8-inch holes. The grommets are difficult to squeeze into the hole, but work at it and you'll get them in. If necessary, use the small edge of a flat screwdriver to push the rubber edges into the holes. In the steps that follow, you assemble all the parts into a box. Use the following figure as a guide for the proper placement of each of the parts. Cut the extension cord. First cut the outlet end of the extension cord, leaving about 12 inches of wire attached to the outlet. Then cut the plug end, leaving about 3 or 4 feet of wire attached to the plug. You'll have a few feet of wire left over; set this wire aside for later. Push the power cords through the grommets and tie a knot inside the box. It will be a tight squeeze, but the cords will fit. Pull about a foot of the cord with the plug attached through the hole nearest the switch. Then, tie it in a knot, cinch the knot down tight, and pull the plug so that the knot is snug against the grommet. The knot acts as a strain relief. Repeat the same process with the cord that's attached to the outlet, passing it through the other grommet, tying a tight knot, and pulling the knot up against the grommet. When both power cords are in place, separate the two wires of each cord inside the project box and strip about 3/8 inch of insulation from each wire. Cut two 1-1/2-inch lengths of extension cord wire and solder them to the switch terminals. You'll need to strip about 3/8 inch of insulation from each end of both wires. Put your soldering iron on its High setting and use thick solder. Set the switch aside when the solder sets. Cut two 1-1/2-inch lengths of extension cord wire and solder them to the terminals on the fuse holder. Again, you'll need to strip about 3/8 inch of insulation from each end of both wires and solder with high heat. Cut two 2-1/2-inch lengths of the hookup wire and strip 3/8 inch of insulation from the ends. Solder one of the hookup wires to the center terminal of the RCA-style phono jack and the other wire to the ground terminal. At this point, you're done with the soldering iron, so you can turn it off. Mount the RCA-style phono jack in the 1/4-inch hole in the project box. To mount the jack, you'll first have to remove the nut, the ground terminal, and the lock washer from the jack. Then, pass the wire connected to the center terminal of the phono jack through the 1/4-inch hole, and then insert the threaded end of the phono jack into the hole. Slip the lock washer, the ground terminal, and the nut over the wire connected to the center terminal, and then thread them onto the threaded part of the jack. Tighten with needle-nose pliers. In the next few steps, you attach wires to the MK110 circuit card. Do not mount the circuit board to the standoffs quite yet. You'll have an easier time connecting the wires if the circuit board is loose. After the wires are all connected, you mount the board. Connect the separated wires of the cord that's attached to the outlet to the two terminals marked Load on the back of the MK110 circuit board. Use a small, flat screwdriver to tighten the terminals. Make sure the wires are securely connected. Connect one of the wires attached to the fuse holder to one of the Mains terminals at the back of the MK110 circuit board. Connect one of the extension cord wires that's attached to the plug to the other Mains terminal at the back of the MK110 circuit board. Connect the two hook-up wires from the phono jack to the input terminals at the front of the MK110 circuit board. The input terminals are labeled LS on the board. You'll need a very small flat-blade screwdriver to tighten these terminals. Mount the MK110 circuit board on the standoffs. To mount the board, you'll need to tilt it a bit to slide the shaft of the potentiometer through the 5/16-inch hole. Once the shaft is through, set the board down on the standoffs and secure it with the remaining four machine screws that came with the standoffs. Use the 3/8-inch 4-40 machine screw and nut to mount the fuse holder. Slide the machine screw through the 5/32-inch hole in the bottom of the project box. Then pass the machine screw through the hole in the center of the fuse holder and attach the nut. Tighten with a screwdriver. Mount the switch. To mount the switch, first remove the plastic nut on the threaded end of the switch. Then, pass the wires and the threaded end of the switch through the 3/4-inch hole in the side of the project box. Finally, slip the nut over the wires and tighten it onto the switch. Connect the switch to the power cord and the fuse. Use one of the screw-on wire connectors to connect one of the switch wires to the unconnected wire on the fuse holder. Then, use the other wire connector to connect the other switch wire to the unconnected wire that leads to the power plug. Insert the fuse in the fuse holder. Guess what — you're almost done! The figure shows the project with all the parts assembled. Attach the knob to the potentiometer shaft protruding from the box. Use a small, flat screwdriver to tighten the set screw on the knob. Place the lid over the project box and secure it with the provided screws. Now you really are done!

Article / Updated 05-09-2017

Other than the Velleman kit itself, most of the materials you need to build a color organ circuit can be purchased at your local RadioShack store or any other supplier of electronic components. The table lists all the materials you'll need. Quantity Description 1 Velleman MK110 Simple Onee Channel Light Organ kit 1 2-x-3-x-6-inch project box (RadioShack part 2701805) 1 20 mm PC board standoffs (package of 4, RadioShack part 2760195) 1 RCA-style phono jack (RadioShack part 2740346) 1 3/4-inch control knob (RadioShack part 274415) 1 Chassis-type fuse holder for 1-1/4-x-1/4-inch fuses (RadioShack part 2700739) 1 1 A, 250 V, fast-acting 1-1/4-x-1/4-inch fuse (RadioShack part 2701005) 1 3/8-inch 4-40 machine screw and nut (for mounting the fuse holder) 1 SPST rocker switch (RadioShack part 2750694) 2 3/8-inch grommets (RadioShack part 6403025) 2 Screw-on wire connectors (RadioShack part 6403057) 5 inches 20-gauge stranded hook-up wire 1 Indoor extension cord

Article / Updated 05-09-2017

There are several different ways to design a color organ circuit. Most of them rely on a special type of electronic component called a triac, which is essentially a transistor that's designed to work with alternating current. It has three terminals. Two are anodes, called A1 and A2, and the third is a gate. A voltage at the gate — either positive or negative — allows the anodes to conduct. The anodes are connected to the line load, and the gate voltage is derived from the audio input. The audio input isn't connected directly to the triac gate, however. Instead, most color organs use one of two techniques to isolate the audio input from the line-voltage side of the circuit. One method is to use a transformer. The other is to use an optoisolator, which is a single component that consists of an infrared LED and a photodiode or other light-sensitive semiconductor. Voltage on the LED causes the LED to emit light, which is detected by the photodiode and passed on to the output circuit. The Velleman MK110 kit uses an optoisolator triac, in which the photosensitive semiconductor is actually a triac whose gate is stimulated by light rather than by voltage. The optoisolator is an integrated circuit in a 6-pin DIP package. The figure shows a simplified schematic diagram for the circuit used by the Velleman MK110 kit. As you can see, the audio input is applied to the LED side of the optoisolator, controlled by a potentiometer, which lets you adjust the sensitivity of the circuit. The output from the optoisolator is applied to the gate of the triac, whose anodes are connected across the line voltage circuit. Thus, the volume of the audio input directly controls the voltage of the output circuit.