© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

Switches and Relays

Electro-mechanical transistor

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

The Switch◦SPST◦SPST Pushbutton NO◦SPDT

The Relay

Power up the board

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

Switches

The simplest switch is the Off-On switch

Also known as the Single Pole Single Throw switch

AKA SPST

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

SPST Pushbutton NO

This switch is Normally Open (NO) or Off

Once pushed it allows power to flow.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

Single Pole Double Throw switch

A SPDT switch is like a railroad switch,

It allows current to flow from one of two paths.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

The Relay

A Relay is a switch that is controlled by an electro magnet.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

When power is applied to the electro magnet, the switch changes state.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

When the power is shut off, the switch returns to its original state.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

Why Use a Relay?

First, the relay can be used to turn on a large voltage with a small one.

Second, it isolates the control circuit from the controlled circuit. In the event of a accident to the controlled circuit like a lightning strike, the control circuit is protected.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

Power up your boardConnect 9V battery/switch to

SW1

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

What Happens Next?

One LED will light up when you power up the board.

© 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE

The second LED will light when you press the button. The first will go out.

This indicates it is changing state.