Hardware Hacking Projects for Geeks

118

Part II: Advanced Hacks, Tools, and Techniques

How to Identify Resistor Values

One of the more common electronic components is the resistor. You can see

what one looks like in Figure II-1.

A resistor reduces, or resists, the flow of electrical current. Think of it as a dam

that holds back water, letting only a certain amount flow through.

A resistor has its resistance value in Ohms marked with color bands on its

side. Each color band represents a number you can plug into the equation

illustrated in Figure II-2. The values for the colors are given in Table II-1.

Hold the resistor so that the

three closely grouped color

bands are to the left

YX x 10

Z

Gold

Silver

(No color)

5%

10%

20%

First digit

of resistance

value

Second digit

of resistance

value

Exponent of

multiplier

Value tolerance

Yellow Purple Red Gold

Example

74 x 10

2

= 4700 (+/-5%) Ohms

Figure II-2: Calculating resistor values

Figure II-1: Resistor

Parallel connection

R

1

R

2

R

total

=

R

1

x R

2

R

1

+ R

2

R

1

R

2

R

total

= R

1

+ R

2

Series connection

Combining Resistors

Resistors can be combined to change

the net value. If two resistors are

combined in series, their values are

added. If they are combined in paral-

lel, their values are determined by the

equations depicted below.

How to Identify Resistor Values

part2.indd 118

1/13/2002 4:11:54 PM