Hardware Hacking - Nicolas Collins

Hardware Hacking 55

Chapter 16: Switches

You will need:

• The electronic toy from the previous experiments.


• Some hookup wire.


• A Single-Pole Double-Throw switch (SPDT,) momentary or toggle.


• Soldering iron, solder & hand tools.

Switches are useful for turning power on and off to a circuit to save battery life,
for turning on and off specific sounds or functions, and for resetting a circuit if it
freezes up. They are often described in catalogs, on websites or in packaging by
arcane abbreviations. Here are the main distinguishing features:

• Mechanical style
  A switch can be momentary pushbutton, like a door bell, that changes state
  (turns something on) when you press it, and returns to its default state (off)
  when you release it; or it can be a push-on/push-off switch that alternates but
  holds states. It can be a toggle switch with a handle, like a traditional light
  switch, that stays where you put it until you switch it back. There is also the
  rotary switch, such as the cycle selector on a clothes washer, with which you
  select between several positions, rather than just on and off. Slide switches, like
  the rotary switch, can select between two or more positions. There are a few
  other oddball switches we’ll discuss if they become relevant.


• Number of “throws”
  A switch is also described by the number of mutually exclusive connections it
  makes when moved or “thrown”. A simple pushbutton that either turn
  something on or does nothing is called a “Single Throw” or “ST” switch. If the
  switch alternates between two possible connections it is a “Double Throw” or
  “DT” switch. Rotary switches that can make several different connections are
  classified by the number of connections – i.e., a 5 position switch would be
  abbreviated as “5T”.

Single Throw (ST) Double Throw (DT) 5-Throw (5T)