Project 1: Let's make a Relay Module - what is relay and how to use it in effective way?
ElectroMagnet Relay:
Relays are very important device when you need to make a switching oriented electronic projects like home automation and so on. This Article will help you to understand the basics of relay and guide you to make a relay module of your own.
What is Relay?:
A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches.
The relay’s switch connections are usually labeled COM(POLE), NC and NO:
COM= Common, NC and NO always connect to this, it is the moving part of the switch.
(below images will explain the working )
NC = Normally Closed, COM is connected to this when the relay coil is not magnetized(i.e not passing the current to coil terminals of relay , in short : if the relay is in off state , the NC pin and COM pin are physically touch each others).
NO = Normally Open, COM is connected to this when the relay coil is MAGNETIZED and vice versa.(i.e when passing current to the coil terminals , NO and COM pin comes in touch with each other , and on not passing current to the coil terminals of relay , the NO and COM will be far apart from each other) .
There are 5 Pins in a relay. Two pins A
and B are two ends of a coil that are kept inside the relay. The coil is
wound on a small rod that gets magnetized whenever current passes
through it.(see the above picture)
COM/POLE is always connected to NC(Normally connected) pin. As current is passed through the coil A, B, the pole gets connected to NO(Normally Open) pin of the relay.
A relay shown in the picture is called as electromagnetic or mechanical relay.
General Specification of Relay:
05VDC- It means that you need 5V to activate the relay. In other words, it means that the voltage across the relay coil has to be 5V-DC.
10A 250VAC 10A 125VAC – The maximum AC current and AC voltage specification that can be passed through NC, NO and pole pins/terminals of relay. Some countries have 220V AC power standard, so, it works in those countries also.
10A 30VDC 10A 28VDC- The maximum DC current and DC voltage specification that can be passed through NC, NO and pole pins/terminals of relay.
Ultimate Tip to find the PIN configuration of Relay:
1.Usually the COM pin is placed in center.
2.Near the COM pin, they are Coil terminals. To ensure that there are coil terminal place the multi-meter(set it to resistor mode ) along the two pins . If you are seeing the readings then they are the coil pins of the relay.
let's make a relay module :
Things need :
BC 547 NPN Transistor *1
5v Relay *1
Connecting wires PCB
Soldering equipments
Header pins and Connector Pins
Connect the circuit as Described in the diagram Below:
Applications of Relay:
The applications of the relay are limitless, its main function is to control the high voltage circuit (230V circuit AC) with the low voltage power supply (a DC voltage).
- Relays are not only used in the large electrical circuits but also used in the computer circuits in order to perform the arithmetic and mathematical operations in it.
- Used to control the electric motor switches. To turn ON an electric motor we need 230V AC supply but in few cases/applications, there may be a situation to switch ON the motor with a DC supply voltage. In those cases, a relay can be used.
- Automatic stabilizers are one of its applications where a relay is used. When the supply voltage is other than the rated voltage, set of relays sense the voltage variations and controls the load circuit with the help of circuit breakers.
- Used for the circuit selection if there exists more than one circuit in a system.
- Used in Televisions. An old picture tube television’s internal circuitry works with the DC voltage but the picture tube needs a very high AC voltage, in order to turn on the picture tube with a DC supply we can use a relay.
- Used in the traffic signal controllers, temperature controllers.
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