Page 233 - 15 Dangerously Mad Projects for the Evil Genius

208 15 Dangerously Mad Projects for the Evil Genius

Components ■ In a pair or as a variable resistor, to divide a
voltage
In this section, we look at the practical aspects of
In the “Theory” section of Chapter 12, we
components: what they do, and how to identify,
looked at Ohm’s law and used it to decide on a
choose, and use them.
value of series resistor for an LED.
Datasheets Resistors have colored bands around them to
indicate their values. However, if you are unsure of
All component manufacturers produce datasheets a resistor, you can always find its resistance using
for their products. These act as a specification for a multimeter. Once you get the hang of it, it’s easy
how the component will behave. They are not of to read the values using the colored bands.
much interest for resistors and capacitors, being
Each band color has a value associated with it,
much more useful for semiconductors and
as shown in Table A-1.
transistors, and especially integrated circuits. They
will often include application notes that contain
TABLE A-1 Resistor Color Codes
example schematics for using the components.
These are all available on the Internet. However, Color Value
if you search for “BC158 datasheet” in your Black 0
favorite search engine, you will find many of the
Brown 1
top hits are for organizations cashing in on the fact
Red 2
that people search for datasheets a lot. These
Orange 3
organizations surround the datasheets with
pointless advertising and pretend they add some Yellow 4
value to looking up datasheets by subscribing to Green 5
their service. In reality, such web sites usually just Blue 6
lead to a frustration of clicking and should be Violet 7
ignored in favor of any manufacturer’s web sites.
Gray 8
So, scan down the search results until you see a
White 9
URL like www.fairchild.com.
Alternatively, many of the component retail
suppliers such as Farnell provide free-of-charge There will generally be three of these bands
and nonsense-free datasheets for pretty much every together, starting at one end of the resistor, which
component they sell, which is to be much is then followed by a gap, and finishes with a
applauded. It also means that you can price and buy single band at the other end of the resistor. The
the components while finding out more about them. single band indicates the accuracy of the resistor
value. Since none of the projects in this book
Resistors require very accurate resistors, there is no need to
select your resistors on the basis of accuracy.
Resistors are the commonest and cheapest
Figure A-3 shows the arrangement of the
electronic components around. Their typical
colored bands. The resistor value uses just the
uses are:
three bands. The first band is the first digit, the
■ To prevent excessive current flowing (see any
second the second digit, and the third “multiplier”
projects that use an LED)