1. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE Switches and Relays Electro-mechanical transistor

2. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE The Switch ◦ SPST ◦ SPST Pushbutton NO ◦ SPDT The Relay Power up the board

3. © 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

4. © 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.

5. © 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.

6. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE The Relay A Relay is a switch that is controlled by an electro magnet.

7. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE When power is applied to the electro magnet, the switch changes state.

8. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE When the power is shut off, the switch returns to its original state.

9. © 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.

10. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE Power up your board Connect 9V battery/switch to SW1

11. © 2010 Akula LLC, Jeremy R. Hertzberg, BS CMPE What Happens Next? One LED will light up when you power up the board.

12. © 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.