Setting up a home lab
In order to build the circuits described in
this volume, you will need a small work area, as well as a
few tools and critical supplies. This section describes the
setup of a home electronics laboratory.
Work area
A work area should consist of a large
workbench, desk, or table (preferably wooden) for performing
circuit assembly, with household electrical power (120 volts
AC) readily accessible to power soldering equipment, power
supplies, and any test equipment. Inexpensive desks intended
for computer use function very well for this purpose. Avoid
a metal-surface desk, as the electrical conductivity of a
metal surface creates both a shock hazard and the very
distinct possibility of unintentional "short circuits"
developing from circuit components touching the metal
tabletop. Vinyl and plastic bench surfaces are to be avoided
for their ability to generate and store large
static-electric charges, which may damage sensitive
electronic components. Also, these materials melt easily
when exposed to hot soldering irons and molten solder
droplets.
If you cannot obtain a wooden-surface
workbench, you may turn any form of table or desk into one
by laying a piece of plywood on top. If you are reasonably
skilled with woodworking tools, you may construct your own
desk using plywood and 2x4 boards.
The work area should be well-lit and
comfortable. I have a small radio set up on my own workbench
for listening to music or news as I experiment. My own
workbench has a "power strip" receptacle and switch assembly
mounted to the underside, into which I plug all 120 volt
devices. It is convenient to have a single switch for
shutting off all power in case of an accidental
short-circuit!
Tools
A few tools are required for basic
electronics work. Most of these tools are inexpensive and
easy to obtain. If you desire to keep the cost as low as
possible, you might want to search for them at thrift stores
and pawn shops before buying them new. As you can tell from
the photographs, some of my own tools are rather old but
function well nonetheless.
First and foremost in your tool collection
is a multimeter. This is an electrical instrument designed
to measure voltage, current, resistance, and often other
variables as well. Multimeters are manufactured in both
digital and analog form. A digital multimeter is
preferred for precision work, but analog meters are also
useful for gaining an intuitive understanding of instrument
sensitivity and range.
My own digital multimeter is a Fluke model
27, purchased in 1987:
Digital multimeter
Most analog multimeters sold today are quite
inexpensive, and not necessarily precision test instruments.
I recommend having both digital and analog meter types in
your tool collection, spending as little money as possible
on the analog multimeter and investing in a good-quality
digital multimeter (I highly recommend the Fluke brand).
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A test instrument I have found indispensable
in my home work is a sensitive voltage detector, or
sensitive audio detector, described in nearly
identical experiments in two chapters of this book volume.
It is nothing more than a sensitized set of audio
headphones, equipped with an attenuator (volume control) and
limiting diodes to limit sound intensity from strong
signals. Its purpose is to audibly indicate the presence of
low-intensity voltage signals, DC or AC. In the absence of
an oscilloscope, this is a most valuable tool, because it
allows you to listen to an electronic signal, and
thereby determine something of its nature. Few tools
engender an intuitive comprehension of frequency and
amplitude as this! I cite its use in many of the experiments
shown in this volume, so I strongly encourage that you build
your own. Second only to a multimeter, it is the most useful
piece of test equipment in the collection of the budget
electronics experimenter.
Sensitive voltage/audio detector
As you can see, I built my detector using
scrap parts (household electrical switch/receptacle box for
the enclosure, section of brown lamp cord for the test
leads). Even some of the internal components were salvaged
from scrap (the step-down transformer and headphone jack
were taken from an old radio, purchased in non-working
condition from a thrift store). The entire thing, including
the headphones purchased second-hand, cost no more than $15
to build. Of course, one could take much greater care in
choosing construction materials (metal box, shielded test
probe cable), but it probably wouldn't improve its
performance significantly.
The single most influential component with
regard to detector sensitivity is the headphone assembly:
generally speaking, the greater the "dB" rating of the
headphones, the better they will function for this purpose.
Since the headphones need not be modified for use in the
detector circuit, and they can be unplugged from it, you
might justify the purchase of more expensive, high-quality
headphones by using them as part of a home entertainment
(audio/video) system.
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Also essential is a solderless breadboard,
sometimes called a prototyping board, or
proto-board. This device allows you to quickly join
electronic components to one another without having to
solder component terminals and wires together.
Solderless breadboard
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When working with wire, you need a tool to
"strip" the plastic insulation off the ends so that bare
copper metal is exposed. This tool is called a wire
stripper, and it is a special form of plier with several
knife-edged holes in the jaw area sized just right for
cutting through the plastic insulation and not the copper,
for a multitude of wire sizes, or gauges. Shown here
are two different sizes of wire stripping pliers:
Wire stripping pliers
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In order to make quick, temporary
connections between some electronic components, you need
jumper wires with small "alligator-jaw" clips at each
end. These may be purchased complete, or assembled from
clips and wires.
Jumper wires (as sold by Radio Shack)
Jumper wires (home-made)
The home-made jumper wires with large,
uninsulated (bare metal) alligator clips are okay to use so
long as care is taken to avoid any unintentional contact
between the bare clips and any other wires or components.
For use in crowded breadboard circuits, jumper wires with
insulated (rubber-covered) clips like the jumper shown from
Radio Shack are much preferred.
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Needle-nose pliers are designed to
grasp small objects, and are especially useful for pushing
wires into stubborn breadboard holes.
Needle-nose pliers
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No tool set would be complete without
screwdrivers, and I recommend a complementary pair (3/16
inch slotted and #2 Phillips) as the starting point for your
collection. You may later find it useful to invest in a set
of jeweler's screwdrivers for work with very small
screws and screw-head adjustments.
Screwdrivers
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For projects involving printed-circuit board
assembly or repair, a small soldering iron and a spool of
"rosin-core" solder are essential tools. I recommend a 25
watt soldering iron, no larger for printed circuit board
work, and the thinnest solder you can find. Do not use
"acid-core" solder! Acid-core solder is intended for the
soldering of copper tubes (plumbing), where a small amount
of acid helps to clean the copper of surface impurities and
provide a stronger bond. If used for electrical work, the
residual acid will cause wires to corrode. Also, you should
avoid solder containing the metal lead, opting
instead for silver-alloy solder. If you do not already wear
glasses, a pair of safety glasses is highly recommended
while soldering, to prevent bits of molten solder from
accidently landing in your eye should a wire release from
the joint during the soldering process and fling bits of
solder toward you.
Soldering iron and solder ("rosin core")
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Projects requiring the joining of large
wires by soldering will necessitate a more powerful heat
source than a 25 watt soldering iron. A soldering gun
is a practical option.
Soldering gun
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Knives, like screwdrivers, are essential
tools for all kinds of work. For safety's sake, I recommend
a "utility" knife with retracting blade. These knives are
also advantageous to have for their ability to accept
replacement blades.
Utility knife
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Pliers other than the needle-nose type are
useful for the assembly and disassembly of electronic device
chassis. Two types I recommend are slip-joint and
adjustable-joint ("Channel-lock").
Slip-joint pliers
Adjustable-joint pliers
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Drilling may be required for the assembly of
large projects. Although power drills work well, I have
found that a simple hand-crank drill does a remarkable job
drilling through plastic, wood, and most metals. It is
certainly safer and quieter than a power drill, and costs
quite a bit less.
Hand drill
As the wear on my drill indicates, it is an
often-used tool around my home!
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Some experiments will require a source of
audio-frequency voltage signals. Normally, this type of
signal is generated in an electronics laboratory by a device
called a signal generator or function generator.
While building such a device is not impossible (nor
difficult!), it often requires the use of an oscilloscope to
fine-tune, and oscilloscopes are usually outside the
budgetary range of the home experimenter. A relatively
inexpensive alternative to a commercial signal generator is
an electronic keyboard of the musical type. You need
not be a musician to operate one for the purposes of
generating an audio signal (just press any key on the
board!), and they may be obtained quite readily at
second-hand stores for substantially less than new price.
The electronic signal generated by the keyboard is conducted
to your circuit via a headphone cable plugged into the
"headphones" jack. More details regarding the use of a
"Musical Keyboard as a Signal Generator" may be found in the
experiment of that name in chapter 4 (AC).
Supplies
Wire used in solderless breadboards must be
22-gauge, solid copper. Spools of this wire are available
from electronic supply stores and some hardware stores, in
different insulation colors. Insulation color has no bearing
on the wire's performance, but different colors are
sometimes useful for "color-coding" wire functions in a
complex circuit.
Spool of 22-gauge, solid copper wire
Note how the last 1/4 inch or so of the
copper wire protruding from the spool has been "stripped" of
its plastic insulation.
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An alternative to solderless breadboard
circuit construction is wire-wrap, where 30-gauge
(very thin!) solid copper wire is tightly wrapped around the
terminals of components inserted through the holes of a
fiberglass board. No soldering is required, and the
connections made are at least as durable as soldered
connections, perhaps more. Wire-wrapping requires a spool of
this very thin wire, and a special wrapping tool, the
simplest kind resembling a small screwdriver.
Wire-wrap wire and wrapping tool
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Large wire (14 gauge and bigger) may be
needed for building circuits that carry significant levels
of current. Though electrical wire of practically any gauge
may be purchased on spools, I have found a very inexpensive
source of stranded (flexible), copper wire, available at any
hardware store: cheap extension cords. Typically comprised
of three wires colored white, black, and green, extension
cords are often sold at prices less than the retail cost of
the constituent wire alone. This is especially true if the
cord is purchased on sale! Also, an extension cord provides
you with a pair of 120 volt connectors: male (plug) and
female (receptacle) that may be used for projects powered by
120 volts.
Extension cord, in package
To extract the wires, carefully cut the
outer layer of plastic insulation away using a utility
knife. With practice, you may find you can peel away the
outer insulation by making a short cut in it at one end of
the cable, then grasping the wires with one hand and the
insulation with the other and pulling them apart. This is,
of course, much preferable to slicing the entire length of
the insulation with a knife, both for safety's sake and for
the sake of avoiding cuts in the individual wires'
insulation.
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During the course of building many circuits,
you will accumulate a large number of small components. One
technique for keeping these components organized is to keep
them in a plastic "organizer" box like the type used for
fishing tackle.
Component box
In this view of one of my component boxes,
you can see plenty of 1/8 watt resistors, transistors,
diodes, and even a few 8-pin integrated circuits ("chips").
Labels for each compartment were made with a permanent ink
marker.
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