Tut 4 : Relay

­­A relay is a simple electromechanical switch made up of an electromagnet and a set of contacts. Relays are quite common in home appliances where there is an electronic control turning on something like a motor or a light. Relays are amazingly simple devices. There are four parts in every relay:

• Electromagnet
• Armature that can be attracted by the electromagnet
• Spring
• Set of electrical contacts

 

It is therefore connected to output pins of the microcontroller and used to turn on/off high-power devices such as motors, transformers, heaters, bulbs, etc. When a current flows through the coil, the relay is operated by an electromagnet to open or close one or many sets of contacts.



Circuit Setup

PBP Program

 

' Example program to activate relay for 1 second and deactivate for 1 second

DEFINE OSC 20 ' using 20MHz clock oscillator
@ device hs_osc

relay VAR PORTD.3    'declare ports
sw1 VAR PORTA.4
          
TRISA=1   

TRISD=0

 

loop:

 

If (sw1=1) Then

High relay

Pause 1000

Else

Low relay

Pause 1000

End If

 

GoTo loop

End