Switches and Relays
Electro-mechanical transistor
© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

The Switch
◦ SPST
◦ SPST Pushbutton NO
◦ SPDT
© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

The Relay

Power up the board
Switches
© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

The simplest switch is the Off-On
switch
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Also known as the Single Pole Single
Throw switch
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AKA SPST
SPST Pushbutton NO
© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

This switch is Normally Open (NO)
or Off
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Once pushed it allows power to flow.
Single Pole Double Throw switch
© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

A SPDT switch is like a railroad switch,
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It allows current to flow from one of
two paths.
The Relay

© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
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.
Why Use a Relay?
© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE

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.
Power up your board

© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
Connect 9V battery/switch to SW1
What Happens Next?

© 2010 Akula LLC,
Jeremy R. Hertzberg,
BS CMPE
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.