Electronics Basics - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 54

The unit of capacitance is the farad (F). Most capacitors are in the microfarad
range, but they can be as small as 1 picofarad (10 -12 F) and as large as 10 4 F in
supercapacitors.
Using Capacitors
If capacitors can store energy, how can this be used? First, capacitors can be
used to regulate power lines, helping to i lter out slight drops in power. Power
lines are thought to be stable, but this is not always the case. Especially in motor
systems, the power levels in power lines can vary. When motors start, they draw
a lot of current, making the voltage temporarily drop. Adding capacitors onto
the power supply helps i lter out those drops and stabilizes the power for other
components. These are described as decoupling capacitors.
WARNING Some capacitors can hold a large charge, and that charge is still there
when you remove the power. Be careful when using these devices. Examples in this
book are limited to 12V, which do not pose a threat, but larger devices like computer
monitors and televisions can contain capacitors that store massive amounts of energy.
Be careful!
One other use for capacitors, and one that is the most used on homemade
electronics, is to help with one of the most basic components: buttons. A but-
ton is a simple mechanical device that will either make an electrical contact
or break it. The problem is that these devices are not perfect, and pushing a
button to make a contact often results in “bounces,” or unwanted spikes, when
the metal inside the switch bounces on the contacts. By using a capacitor, the
bounces can be i ltered out.
Diodes
A diode is a small component that allows electricity to l ow in only one direc-
tion. A perfect diode would not have any voltage drop and would not allow
any electricity to l ow in the opposite direction, but we don't live in a perfect
world. Diodes do in fact have a voltage drop depending on the type of diode
you use. A silicon diode like the 1N4148 have a voltage drop of approximately
0.65 V. Germanium diodes have a voltage drop of about 0.3 V.
Also, diodes have something called a breakdown voltage , the reverse voltage at
which a diode conducts in reverse and most often breaks the component. The
1N4148 has a breakdown voltage of at least 100 volts, something that you will
not encounter in the examples in this topic, but it is useful to know.
Diff erent Types of Diodes
There are many types of diodes. This topic presents only the most common
diode. Other types of diodes exist; Zener diodes have a specii c breakdown