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How to use relay example of basic schematic circuit diagram?

How to use a relay with circuit diagrams?

A switch operated electrically is known as relay. The current passing through relay’s coil. The coil will generates a magnetic field which is attracting a lever & changes contacts of switch. The current of coil can be on or off so, relay has two switch positions & it is double throw (changeover) switch. So, the answer of question is that how to use relay? (Mentioned in the topic “How to use relay example of basic schematic of relay circuit diagram”).

basic schematic circuit diagram of relay example

Switch connections of relay are mostly named as POLE /COM, normally Close(NC) & normally open (NO):Pole and COM is equal to Common, normally closed and normally open is always connected with the moving  part of the switch. Normally close, POLE /COM is attached with coil when the coil of relay is nu-magnetized. Visa versa Normally Open, POLE /COM is attached with coil when the coil of relay is magnetized. Some example is show in below:

mechanical relay example


electromagnetic relay diagram




Relay and its symbol

Symbol of relay:

The total pin in relay is five. The two pins are attached with coil are A and B, the coil in kept inside the relay. The coil of relay is wrapper on some conductor rod .when current is passes from it they get magnetized. POLE/COM is always attached to normally connected (NC) pin. When current flow from A and B due to magnetism POLE is attached to the normally opened (NO) pin of relay.

Working of relay:

It has some electromagnetic switching system that mean it have a coil and switch in it. When the current is passes from the coil. It react like a magnet and switch or some metal plate attract toward the coil. When plate and coil are connect so circuit I complete current will pass through it. This make system on and off.

Read>>optimizing basic circuit schematic diagram



 Basic schematic circuit diagram of Relay

The following schematic shows the basic circuit.

relay switch device of basic schematic circuit

Connect the relay with HC11 port pins this is used to control on switches.

The transistor allows the HC11 to control the medium sized coil current of relay. The diode prevents relay from arcing by giving a return path for the energy stored in the magnetic field of coil, extending the life of relay.

How can we identify the pins of relays?

To identify the pins of relay you want ohmmeter. Ohmmeter is used for measuring the resistivity of an element then we measure the resistance of all pins in relay. The two pins which resistance is low not 0 Ohm it’s round about 300 Ohm to 350 Ohm then these pins are coil pins of relay. After finding coil pins then used the Ohm-meter as continuity checker to check that which pins are connected with each other when the relay is charged and discharged. By this process you can find the switching system of relay.

There are different type of relays available there, so different type of relays has different type of switching system. This may be difficult some time to identify there is an example below. For example, different relays has many switch in parallel. The other type of relays is known as latching relays, the major different is they have more than one coil and latching mechanism in it. This latching relay is working on momentary pulse. This pulse are used for switches the switch. This switch will not stop the working until we put pulses on different coil.

Why we use diode with relay circuit

Whenever an electro-mechanical relay is dis charge quickly by the automatic switching system or a semiconductor, the dropping magnetic field creates a basic temporary  voltages of we have to remove this stored energy  and also manage the the change in flow of current. A 12 V DC relay, for instance, probably can produced a voltage of 1000 volts – 1500 volts when we turn off them. So it is very usual to put out the relay coils with those electric components which capacity is  the summit voltages to a much smaller level which gives a path for discharging the magnetic stored energy from the relay coil.

This is not a best practice to use flyback diode to stop the backflow of current. There are few ways to overcome this problem:

  1. A bilateral temporary vanquish diode
  2. A reversed-biase diode is conected in series with a resistor.
  3. A Zener diode in series with reverse-biase diode a (MOV) metal-oxide-visitor.
  4. When conditions allow to use transistor, is often put out the current shock
  5. Don’t used reverse biased diode.
  6. Don’t used resistor and capacitor as “Shock absorber”.

The two wire wound coil. The second winding used as the crackdown of device. This type of winding is not used because it is costly and increased in size of relay.
In above we discuss the bad practice. Now discuss some good practice, in relay Zener diode in parallel to the coil and the coil is used as reverse biased rectifier diode. This allows the relay to have best release dynamics and a better contact life.







If the relay is not working or not performing the activity then you are using wrong voltage coil. Mostly 12 volt coil is used in relays, but few relays have 5 volt coil. 5 volt coil relays are easy to use, so you don’t need high power supply. Five volt coil relays are easier to use, since you don’t need to a high voltage power supply. If you are using 12 volt coil relay on board, you will use nine volt coil relay instead of 5volt coil relay, as shown in the schematic.


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