Choosing Electronic Parts for Your Project – Part 1
This blog series attempts to show you how to design, program, build, and test your prototypes, eventually turning those prototypes into production-worthy gadgets. Every electronic circuit need is different, however, and your solution to your problem will need specific circuits to solve that problem most efficiently and cost effectively.
So you have an idea for an electronic gadget…great! The trickiest step in the whole process is figuring out which electronic components, or parts, are needed to make up your circuits. This is not a step to be taken lightly. There are a billion ways to solve any problem and seemingly a billion parts out there to help you do it. First off, you have to find the components that make your solution possible, and then you will likely need to refine the design such that it is economically viable and power efficient. There are so many parts out there that it is hard for anyone to know all of the possible options. It takes a lot of research.
Often, electronics designers stick to what they know and have experience working on from past projects. This is with good reason; part specifications can be long, confusing, and sometimes inaccurate documents. Designing with something that you already know can vastly improve the chances of the prototypes working in short order. However, technology is always moving forward, and new parts can combine functions of other parts or improve cost and performance over past technologies.
This section aims to give you an overview of the types of parts that are available and teach you the terminology necessary to find the types of parts needed to solve your circuit problem. Your parts will be identified by a set of specifications that detail exactly what the parts can do, how much power they consume or dissipate, the temperature they can withstand, how they mount to your board or how they are packaged, the type of material makeup, and their size and weight. This is just for starters.
The best resource at your disposal to learn about the available options are the electronic part distributors such as Mouser, Digikey, Arrow, Avnet, and Newark, but prepare to be overwhelmed with choices! You can also find harder-to-find or specialized parts on eBay and Alibaba.
This post starts with the basic circuit elements and works up to the more interesting active, smart circuit devices.
Note About Packaging
The packages of electronics components refer to how the parts mount to the circuit board. Most parts are either soldered to a Printed Circuit Board (PCB) with a through-hole method or with Surface Mount Technology (SMT). Within the SMT category, devices can utilize legs, pads, or balls to connect to the PCB. Some parts can be wired into your circuit through wire terminals or lugs. Yet other devices can utilize specialized connectors between the device and the circuit board.
Foundational Electronic Components
The simplest of all components are discrete passive components. These parts only have a singular purpose, such as offering resistance, capacitance, inductance, or adding a voltage or current control. Most discrete components only have two or three pins. Although these are very simple devices in theory, there are still a million choices to be made regarding the construction of each device. Electronics engineering is a very specific industry, so be prepared for that.
Resistors offer electrical resistance to a circuit. Resistance is measured in ohms, designed as Ω. Parts are ordered according to the resistance as well as the current capacity of the device. Resistors are packaged most commonly in either a through-hole or SMT package. Resistors have no polarity and can be installed in any direction. Resistor networks are parts that combine multiple resistors together in the same package in order to save space on the board and simplify assembly.
Potentiometers are variable resistors that have three terminals. The potentiometer is simply a resistor that has third pin to act as a mechanical “wiper” that allows the resistance between terminals 1 and 2 or 2 and 3 to be varied. Potentiometers can be used to allow user input into a circuit, for example a volume knob on a stereo. They can also allow fine tuning of a design during the production process. Potentiometers are ordered according to the total resistance offered and the degrees of turn, or number of turns that the wiper allows. Higher accuracy and more turns increases the cost. Potentiometers have no polarity are packaged in through-hole and SMT packages for production but are commonly implemented with wire lugs.
Capacitors store electrical charge. Capacitors have many applications in filtering of frequencies. They can be used to store charge for a power regulator circuit or to dampen frequency response of a circuit. Capacitance is measured in Farads designated as F, most commonly in micro, nano or pico Farads, designated as µF, nF, or pF. Capacitors are packaged most commonly in either through-hole or SMT packages. Electrolytic capacitors have a polarity and must be installed such that the positive lead is always more positive charge than the negative terminal, or else the capacitor could be destroyed. Non-electrolytic capacitors have no polarity constraints. When ordering capacitors, you must specify the type of polarization, the type of dielectric (i.e. ceramic, plastic, paper, etc.) the voltage rating, and the amount of capacitance offered. There are many different types of capacitors that have many specific uses.
Inductors store electrical energy in a magnetic field. Like capacitors, inductors are primarily used in filtering of frequencies. Inductance is measured in Henries, most commonly in micro or nano Henries, designated as µH or nH. Inductors are packaged most commonly in either through-hole or SMT packages. Inductors have no polarity constraints.
Ferrite beads, also known as chokes, offer impedance to a circuit. Ferrites are primarily used to prevent high-frequency noise from propagating past them and are often found on the end of cables that connect devices together. They can be ordered in through-hole, SMT or as a wire shield.
Transformers are essentially two inductors that are packaged together to transmit alternating current (AC) power from one circuit to another through electromagnetic induction. They are commonly used to transform an AC voltage from one value to another. The number of windings in each inductor dictates how the voltage will be transformed. In this way, they are a simple AC voltage converter, based upon how the transformer is constructed. Transformers can be packaged in a variety of different packages from SMT all the way up to house-sized buildings for commercial power delivery.
Diodes are devices that either permit or block the flow of current in a circuit, based on the voltage on its terminals. The current can only flow if the anode terminal is at a higher voltage than the cathode terminal, usually by at least 0.7 volts. Diodes are like a one-way valve for voltage, and prevents voltage from going the wrong way. They are used in power conversion from AC to DC and to protect circuits from an out-of-bounds voltage input. A Zener diode is a special kind of diode that is used as a power regulator. A Schottky diode has a lower forward voltage drop (in the 0.15 to 0.45V range) and a faster turn-on time.
Light Emitting Diodes (LEDs) share many of the same properties with normal diodes, covered above, but are primarily used to generate light.
Photo Diodes perform the opposite function of LEDs, whereby they produce electrical current if light is present. These devices are useful to detect the presence of light.
Transistors are versatile circuit elements that are the most complicated of the passive discretes on this list. The three-pin devices can be used as voltage or current-dependent switches, or as power amplifiers or regulators, depending on the circuit. If you have a problem, there is a solution that can be created with transistors, as a microprocessor is at its heart a very large collection of transistors. There are two general technology types, Bipolar Junction (BJT) and Field Effect (FET.) These two types of transistors differ in pin terminology. The BJT transistors have two sub types, known as NPN and PNP which describe the polarity of the component. The FET transistors have many sub types that pertain to n-channel and p-channel. Note that the direction of the arrows in the symbol change based on the type of transistor it is describing.