Parts needed for electronics and radio construction
The components in most electronics constructors' projects are a mix of what they buy specifically for it and what they already have on-hand.
On-hand parts are either salvaged or common items that you've stocked up on. Stocking up is sensible as it gives you freedom to start and
complete projects when you want. Then you won't have to travel an hour to pick up a dollar part or wait for an online order to arrive.
Tools and test gear
Before you build anything electronic you'll require some basic tools and test gear.
Homebrewing for the novice has a good list of what you'll need.
Salvaging parts
Salvaging is great if you're on a budget or you need specialised parts that aren't so easy to find new. Examples of less common but potentially
useful parts include RF transistors, high voltage capacitors, polystyrene and NPO ceramic capactors, high wattage resistors, potentiometers,
variable capacitors, crystals and ceramic resonators, RF chokes, toroids, rotary switches, transformers (for the enamel copper wire) and more.
Also don't overlook enclosures, sockets, knobs and hardware. Currently available types may be the wrong size or expensive so a good variety
of salvaged parts on-hand is desirable.
Once you've got an old item to salvage you can spend hours desoldering parts from the board. My advice is not to bother. The parts are probably
safer and less likely to be damaged if they remain on the board. Instead I suggest removing the board from the case and storing the boards in
cardboard boxes or tubs. If the case and other bits aren't needed they can be discarded, greatly saving space. Then when you need a part go through
the salvaged boards and desolder what's needed.
Some component types and values are used over and over again in electronics projects. Other types and values are hardly used. If you want to build
up a stock of parts you want more of the commonly used items and fewer of the less used parts. Otherwise you risk wasting money on components
you'll never use.
I'll run through the main electronic components people use in projects and discuss what is and isn't worth buying when stocking up. Note though that
everyone builds different things and what's common for me (as one who builds a lot of radio gear) won't be the same for a maker into (for example) robotics.
Resistors (fixed value)
Resistors restrict the flow of current in a circuit. Common applications include allowing LEDs to run from a higher voltage, biasing transistors, voltage dividers for instance
in op amp circuits, adjusting gain of amplifier stages, determining frequency of audio oscillators and filters and to provide audio and radio frequency attenuation.
Almost anything electronic you build will have a lot of resistors. Which is fortunate since they are very cheap (only a few cents each) and they are typically only sold in bulk packs.
Values vary from under 1 ohm to 10 megohm (10 million ohm). The most commonly used values in electronic circuits would be 10, 22, 47, 100, 220, 470, 1k, 2.2k, 4.7k, 10k, 22k, 47k, 100k, 220k, 470k
and 1M. However you will also see some in between values, eg 15/150/1.5k/15k/150k, 33/330/3.3k/33k/330k, 56/560/5.6k/56k/560k, 68/680/6.8k/68k/680k and 82/820/8.2k/82k/820k values.
If you don't have a particular value you can connect two of the same value resistors in parallel to halve the marked value or in series to double it.
There are some cases where you'll need a lot of resistors of similar value. For example if you mess around with LEDs a lot you'll use a lot of resistors between about 220 ohm and 1.2k to provide
appropriate current from your 5 to 15 volt supply rail. Similarly LM386 amplifiers use a lot of 10 ohm resistors. If your construction is like that then consider buying a multi value resistor
pack along with some single value packs for the few types that you'll most need.
Resistors are typically within 5% or 1% of their marked value. In many cases even a 20% difference won't adversely affect circuit performance. So if you see a circuit and don't have the exact resistor
value try a nearby one as it will likely still work. The most common resistors are rated at 1/4 watt which is fine for low power transistor and IC circuits. Higher power resistors are rated at 1 watt,
5 watt, or higher ratings. Generally speaking the physically bigger the resistor the higher the current rating. Cheaper resistors are carbon film which is fine for most hobby uses. Metal film resistors are better for more critical applications. Power resistors are often wire wound.
Capacitors (fixed value)
Capacitors store electrical charge in a circuit. Common applications include power supply filtering, coupling signals between stages, isolating circuit stages from one another (to prevent unwanted
interaction or feedback), timing applications, audio and radio frequency filtering and as part of the frequency determining element in audio and radio frequency oscillators.
Again, like resistors, almost everything electronic will have capacitors. But unlike resistors there's a greater diversity of types and values with capacitors. There is often, except in critical
timing or filtering applications, more latitude in capacitor values you can use. For example if a circuit calls for a bypass capacitor value of 100nF (or 0.1 uH) then either 47 or 220nF will
probably work fine.
There are several main types of capacitor. Disc ceramic are available from very low values (eg 1pF) through to over 100 000 times this (or 100nF ie 0.1uF). They are cheap and good for audio and
radio frequency circuits. NPO types are particularly prized for the latter since they don't vary value with temperature (what's known as having a zero temperature coefficient). If you want a good
general purpose type capacitor for many applications then disc ceramic is a good choice to order. If you want to know what they look like, go to your local supermarket and find the lentil aisle.
Disc ceramic capacitors are the same size and colour and are only distinguishable by the wires sticking out. Disc ceramics are typically rated at 50 to 100 volts, making them suitable for low
power transistor and IC circuits, although high voltage types (often coloured blue) are also available.
Another type of medium value capacitor is the polyester film or 'greencap', so called due to their most common colour. Typical values range from 1nF (1000pF or 0.001uF) to about 1uF. They are a
bit bigger than disc ceramics. They are most common in audio equipment. When you get some experience you'll almost be able to tell their value by looking at them as the physically bigger they
are the higher the value. Common voltage ratings are 50 or 100 volts, but special types are suitable for high voltages, such as you might use for mains electricity or high tension applications.
Monolithic capacitors are used in similar applications to greencaps but often have a yellow squarish case.
There are two main types of higher value capacitors. These are tantalum and electrolytic. They sound different when they explode (such as when excess voltage is applied). Also an electroytic
capacitor sends more fluff than you think could ever fit in its metal can when it does. Both start off at about 0.47uf and go up to many microfarads. In the case of electrolytics 10 000uF or more.
Common applications include power supply filtering and audio amplifier bypass and coupling. These do not call for very precise values and you could use either half or double the specified
value and not notice the difference. Voltage ratings need to be strictly observed with a bit of leeway for safety. Eg it's bad engineering to specify a 16 volt rated capacitor for a 12 volt circuit.
Instead go with a higher rating like 25, 35 or 50 volt.
Capacitors you won't come across unless you're into radio or vintage electronics are mica, silver mica and polystyrene. These are rare. However they are good for sensitive radio frequency
applications in places where you might use an NPO disc ceramic. They were typically made in low values only (10pF to 1nF) and may have high voltage ratings suitable for high power RF stages.
What's the most common value of capacitor used in projects?
Without a doubt it would be 100nF (or 0.1uf). These are used by their millions in bypassing and decoupling applications. Typically you'd
have one from the power pin of a digital IC (typically pin 8 for 8 pin, pin 14 for 14 pin or pin 16 for 16 pin) to ground. This ensures a clean supply and reduces the transmission of noise along
supply lines. It's also a common value in many HF RF oscillator and amplifier circuits. Even if you get a multi-pack with several 100nF types includes you'll run out unless you also by a large number
seperately.
Simple transistor and IC audio amplifiers often use 10uF and 100uF values (either tantalum or electrolytic) so get plenty of these. Op amp circuits often call for lower values (which can either be ceramic
or greencaps) like 2.2, 4.7, 10, 22, 47 or 100nF. Radio frequency circuits may use 10nF for bypassing with common values for filtering, tuned circuits and coupling purposes between 1pF and 10nF.
Diodes
Diodes (or rectifiers) conduct current in one direction only. Uses include converting AC to DC, radio signal mixing and detection, voltage regulation, reverse polarity protection,
voltage dropping, capacitance, lighting, and more. Generally the bigger the diode the higher its current handling rating.
The most common type is the basic small signal silicon diode (eg 1N914 or 1N9148). Every electronics builder needs a packet. Higher power silicon diodes (eg the 1N4000 series) handle
higher current than the 1N4148 type and are suitable for power applications. Also useful are 'bridge rectifiers' which are four diodes in the one package. Again useful for power supplies.
Zener diodes, with voltage ratings from about 3.3 volts up to 30 volts or more can provide voltage regulation for low current applications in conjunction with a suitable resistor. Voltage
regulation is important for sensitive circuitry whose performance characteristics undesirably change when its supply voltage varies. Light emitting diodes are perhaps the most well-known
type of diode, wth lighting, display and status indicator applications in projects. Unlike a globe they are current sensitive and need to be wired in series with an appropriate current limiting
resistor suitable for the supply voltage used.
Lesser known diodes include the germanium and varactor diodes. Both are primarily used in radio applications. The germanium diode is more sensitive than the silicon diode so is widely used in
small signal radio applications like crystal set receivers, AM detectors and RF probes. The varactor diode changes capacitance when the DC voltage applied to it is varied. This makes it useful
for applications such as variable frequency oscillators, FM modulators and frquency multipliers. All diodes exhibit this effect but varactors have been optimised for this application.
Transistors
Transistors are central to discrete component electronic circuitry. They perform a wide variety of amplification, oscillation and switching functions. The most common bipolar junction transistor is
NPN, with the collector more positive than the base which is more positive than the emitter. PNP transistors are similar except the polarities are reversed. Some circuits (most notably audio
amplifiers) require both to work. There are many different part numbers but a common type such as 2N3904, BC548 or 2N2222 (NPN) or 2N3906 or BC558 (PNP) will work in simple circuits like you see in
Talking Electronics. For a little more power devices like the BD139 (NPN) or BD140 (PNP) are good, even up to about 10 MHz.
Field effect transistors have different connections (gate, source, drain). They are less common than bipolar transistors but are used in certain amplification
and switching applications. MOSFETs are a variation used in high power switching applications.
Small signal transistors of both types are typically in a black plastic semi-cylindrical package called the TO-92. Higher powered transistors are in bigger packages
like TO-5, TO-3 or TO-220. These are metal and are able to have a heat sink screwed or clipped on to dissipate heat generated.
Integrated circuits
Integrated circuits have revolutionised electronics and made construction easier. Commonly used linear types include the 741 op amp (and newer lower noise derivatives), 555 timer and LM series
voltage regulators. The simpler logic ICs typically included four AND, OR, NAND or NOR gates in the one package. Other common types include inverters, flip flops, counters, dividers,
oscillators, phase locked loops and more. More recently we have seen the rise of programmable electronics, based on PICs and microcontrollers. Gathering the collection below
will assist with building many projects.
Arduino bits and pieces
Beginners in Arduino normally commence with a starter board. The Ardino IC will be on a pre-soldered board with a voltage regulator, crystal, LEDs, sockets etc. Shield boards plug in to
provide additional functions. But if you're building an Arduino based project from scratch you might want a different arrangement. Or you might prefer to keep your Arduino board intact for
future experiments prototypes. Fortunately the extra parts needed to make your project independent are readily available.
Circuit boards
Most builders will want some sort of circuit board for their project. Solderless breadboard is good for protyping, especially for IC non-critical IC projects that operate at DC and audio frequencies.
Once satisfied with a design you can use a more permanent mounting method involving soldering. Possibilities include pre-punched matrix board, pre-punched strip board or a printed circuit board.
I'm a fan of matrix board (without the strips) for simple transistor and IC projects. Alternatively you could use strip board (known as Vero board in some countries) and use a drill bit to break
unwanted connections between strips. For radio frequencies I prefer 'dead bug' style of contruction on a piece of unetched printed circuit board to minimise stray capacitance. Below are some supplies
to gather to ensure you're never without circuit board for a project.
Variable capacitors
Variable capacitors are useful in many radio project applications. They often form the tuning element in simple transmitters and receivers that use free-running
or variable crystal oscillators. Front-end receiver preselectors or transmitter band pass filters may use variable capacitors. And in conjunction with an inductor they provide
impedance transformation such as done by antenna couplers.
The better variable capacitors have air spaced plates. These are more stable in value and can accommodate higher voltages before they break down. The cheaper and smaller types
use plastic dielectric. Stability and voltage ratings are less but you can get away with them for many homebrew applications, such as in variable crystal oscillators and QRP
antenna couplers.
Then there are trimmer capacitors. These are good where only occasional adjustments are needed. For example band pass filters in transceivers or aligning
crystal oscillators to an exact frquency. There are air and plastic dielectric trimmers. Those with a half-turn from maximum to minimum capacitance generally have a low maximum
capacitance range (eg 10 to 100 pF). Whereas mica compression trimmers which need several turns often have a much higher maximum values.
If you are using a variable capacitor for a main tuning on a receiver, the half turn of the shaft doesn't allow easy tuning especially if the tuning range is more than about 30 - 50 kHz.
To help you need some sort of mechanical reduction or gearing between the tuning knob and the variable capacitor. Though expensive, a vernier reduction drive and dial is a good addition
as it makes tuning much easier. For example a 6:1 drive would mean that instead of 1/2 turn to tune the full range of your receiver or transmitter you cover it in 3 turns of the tuning knob.
Mechanical reduction is particlarly helpful for SSB gear or CW equipment with narrow filters due to their more critical tuning.
Inductors
Inductors (or coils) are another widely used component in circuits. In conjunction with capacitors they can form filters that offer higher suppression of some frequencies than others.
Depending on how they are connected they can be set up to:
(a) pass signals of a particular frequencies (band pass filter)
(b) reject signals of a particular frequency (band reject or notch filter)
(c) only pass signals that are below a particular frequency (low pass filter), or
(d) only pass signals that are above a particular frequency (high pass filter)
These functions are very useful to allow selection of stations (ie tuning) in receivers or filtering in transmitters so that their output is clean and any interference is minimised.
Another type of inductor, normally comprising two or three separate lengths of wire twisted together, may pass a broad range of frequencies but form a transformer to step up or
step down impedances. This is required to ensure efficient power transfer between stages in a transmitter or receiver or between a transmitter final amplifier and the antenna.
Another antenna application is as a balun, allowing a balanced antenna (such as a loop or dipole) to be connected to coaxial cable without the risk of feedline radiation.
Whereas one function of capacitors (discussed before) is to effectively short unwanted radio frequencies to earth, one use of inductors is to ensure that radio frequencies are not shorted
to earth (as doing so would ruin the function of a stage such as an RF amplifier). A clue that this is a function of an inductor you see in a circuit is if it is labelled 'RF choke'
(which is really just a high value inductor relative to the RF being isolated).
Inductors are less used in non-radio circuits but one application where they are handy is to lessen unwanted AC noise transmission (or transients) through various parts of a circuit or
from its power supply. This is particularly important in sensitive circuitry such as high gain audio amplifiers that are prone to feedback and hum.
Inductors are wound either on a non-metal cylinder or (more often) on a toriod. You can get them in prewound forms (particularly for RF chokes whose exact value is often not that important)
or buy the parts to wind your own. The latter typically involves a toroid plus suitable (often enamel-covered) copper wire between approx 0.1 and 1mm diameter. This can be salvaged from
old transformers or bought new.
The most common toroid types
include ferrite (dark grey colour) most used for balun transformers and iron powder (most commonly coloured red or green) for RF tuned circuts and filters. Larger toroids are handy if you
need to accommodate many turns of wire (for high inductance values) or need to handle high amounts of RF power.
Toriods have an identification code that indicates their size and material type. For instance an FT50-43 is a ferrite toroid that is 0.5 inch (13mm) in diameter using type 43 ferrite material.
A FT37-43 would be a similar but smaller part (0.37 inch (10 mm) diameter. In radio frequencies type 2 or type 6 is most common for iron powder toroids as used in tuned circuits and filters. Type
2 toroids are red and are best for lower and middle HF frequencies. Type 6 toroids can also be used for higher HF and lower VHF frequencies and can be identified from their yellow colour. The code again
indicates this. For instance a T50-2 is a red 0.5 inch diameter toroid using type 2 material whereas a T200-2 is a 2 inch (51 mm) diameter version. Whereas a T37-6 is a yellow 0.37 inch diameter type
using type 6 material.
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