User Manual

63
Lesson 7 Relay
Introduction
As we know relay is a dev ice which is used to prov ide connection between two or more
points or dev ice in response to the input signal applied. I n another w ords relay provide
isolation between the controller and the device as we know dev ices may work on AC as well
as on DC. However, they receive signals from microcontroller w hich works on DC hence we
require a relay to bridge the gap. Relay is extremely useful when you need to control a large
amount of current or v oltage with small electrical signal.
Components
- 1 * Raspberry Pi
- 1 * Breadboard
- 1 * Relay
- 1 * LED
- 1 * Resistor (220Ω)
- 1 * Resistor (1KΩ)
- 1 * NPN Transistor
- 1 * Diode (Rectifier)
- Sev eral jumper w ires
Principle
Relay
There are 5 parts in every relay:
1. Electromagnet – It consists of an iron core wounded by coil of wires. When electricity is
passed through, it becomes magnetic. Therefore, it is calLED electromagnet.
2. Armature – The movable magnetic strip is known as armature. When current flow s through
them, the coil is it energized thus producing a magnetic field which is used to make or break
the normally open (N/O) or normally close (N/C) points. And the armature can be mov ed
with direct current (DC) as well as alternating current (AC).
3. Spring – When no currents flow through the coil on the electromagnet, the spring pulls the
armature away so the circuit cannot be completed.
4. Set of electrical contacts – There are two contact points:
． Normally open - connected when the relay is activ ated, and disconnected when it
is inactive.
． Normally close – not connected when the relay is activ ated, and connected w hen
it is inactive.
5. Molded frame – Relays are cov ered with plastic for protection.
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