Raspberry Pi A, Руководство пользователя, Страница: 222 / 314

P A R T I V
H A R D W A R E H A C K I N G
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Work stand —Commonly referred to as helping hands , these are weighted stands with
clamps or clips that hold the item to be soldered in place. Some work stands include an
integrated magnifying glass for delicate work, while the most expensive work stands
add a light to help illuminate the work area.
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Multimeter —Multimeters are test meters that have multiple functions including
voltage, resistance and capacitance measurement, along with continuity testing for
finding breaks in circuits. Although a multimeter is not an absolute necessity, it can be
extremely useful for diagnosing issues with circuits. Professional multimeter units can
be quite expensive, but a simple model is fairly inexpensive and is a sound investment
for anyone getting started in electronics.
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Desoldering wick
—Mistakes happen, but they don’t have to be permanent. A desol-
dering wick is a braided metal tape that can be placed over a solder joint and heated,
pulling the solder away from the component and into the wick. With practice, it’s pos-
sible to use a desoldering wick to salvage components from discarded electronic equip-
ment—a handy way to gather common components cheaply.
Reading Resistor Colour Codes
Most electronic components are clearly labelled. For example, capacitors will have their capac-
itance , measured in farads , printed directly on them, while crystals will have their frequency
likewise marked.
The major exception is a resistor, which typically has no writing on its surface. Instead, the
resistance value in ohms is calculated from the colour bands that adorn the resistor’s surface.
Learning to decode these bands is an important skill for a hardware hacker to learn, because
once a resister is removed from its packaging, the only way to figure out its value is to use a
multimeter, which is an awkward and slow measuring tool for this particular job.
Thankfully, the resistor colour codes follow a logical pattern. Figure 13-1 shows a typical
four-band resistor. A high-resolution colour version of this diagram is available on the
Raspberry Pi User Guid e website at
www.wiley.com/go/raspberrypiuserguide2e
. The
first two bands are assigned a colour that equates to a resistance value in ohms. The third
band is the
multiplier, by which the first two numbers are multiplied to arrive at the actual
resistance value. The final band indicates the tolerance of the resistor, or how accurate it is. A
resistor with a lower tolerance will be closer to its marked value than a resistor with a higher
tolerance, but you’ll pay more for the component.