What you are expected to learn

At the end of this module, you should be able to:

• define a switch
• list different types of switches
• illustrate the schematic symbols of the different types of switches

How to learn from this module

Going through this module can be both a fun and a meaningful learning experience. All you need to do is make use of your time and resources efficiently. To do this, here are some

tips for you:

1. Take time in reading and understanding each lesson. It is better to be slow but sure than to hurry finishing the module only to find out that you missed the concepts you are supposed to learn.

2. Do not jump from one chapter to another. Usually, the lessons are arranged such that one is built upon another, hence an understanding of the first is essential in comprehending the succeeding lessons.

3. Be honest. When answering the test items, do not turn to the key to correction page unless you are done. Likewise, when performing experiments, record only what you have really observed.

4. Safety first. Perform the experiments with extra precaution. Wear safety gears whenever necessary.

5. Don’t hesitate to ask. If you need to clarify something, approach your teacher or any knowledgeable person.

What to do before (Pretest)

Lesson 10: Switches

A switch is a component that allows us to control whether the current is on or off in a circuit. A closed switch has practically zero resistance, whereas an open switch has nearly infinite resistance.

A simple switch shown in the schematic symbol above can control only one circuit. Switches can be classified according to their contact behavior such as the following,

1. single-pole, single-throw or SPST
2. single-pole, double-throw or SPDT
3. double-pole, single-throw or DPST
4. double-pole, single-throw or DPST

The term pole is defined as the number of completely isolated circuits that can be controlled by the switch. The term throw is defined as the number of closed contact positions that exist per pole.

An SPST (single-pole, single throw) switch as shown in the figure can only make or break a single circuit path. It is used for circuits where the only intent is to turn on or turn off a single circuit path.

A SPDT switch or single-pole, double-throw switch can be used to control two loads although not simultaneously.

Another type of switch is the DPDT or double-pole, double-throw switch. This type of switch may be used to make or break two different circuits at the same time.

Switches can also be classified according to their mechanical construction. Some examples are the following,

1. toggle switch: A switch having a mechanism that snaps into the on or off position at the opposite extremes to which a lever is moved.
2. slide switch: A switch actuated by sliding a block shaped button.
3. rocker switch: A toggle switch whose lever is a specially
4. shaped bar. The bar is rocked back and forth to operate the switch.
5. pushbutton switch: are often spring-loaded switches that are either normally open (NO) or normally closed (NC).
6. lever switch: A switch designed for rapid making and breaking of a circuit.
7. reed switch : A frequency-sensitive switch in which the movable contact is mounted on the tip of a thin, metal strip (reed). The reed is actuated by an alternating-current (ac) coil. The reed closes the contacts when the ac excitation is at its natural frequency.
8. Dual Inline Package (DIP) Switch: It consists of eight miniature rocker switches, where each switch can be set separately. A DIP switch has pin connections that fit into a standard IC socket.
9. Rotary Switch: A switch in which a blade moves in a circle or in arcs over the contacts.
10. Float Switch: A switch operated by a float, such as in a sump pump.

Important Terms

• Pole the number of completely isolated circuits that can be controlled by a switch.
• Switch a component that controls whether the current is on or off in a circuit.
• Throw the number of closed contact positions that exist per pole on a switch.

Self Check