A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
Relays are used for:
1) Amplifying a digital signal, switching a large amount of power with a small operating power. Some special cases are:
2) A telegraph relay, repeating a weak signal received at the end of a long wire.
3) Controlling a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers.
4) Controlling a high-current circuit with a low-current signal, as in the starter solenoid of an automobile.
5) Detecting and isolating faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),
6) Isolating the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors to conserve energy.
A) Now you only have to do is to make 2 circuits.
B) First circuit is very easy as you can see in the pictures about this. This circuit is made by the children in schools. I hope you will have no difficulty in making this.
C) Now ready to make the 2nd circuit. This is the easiest circuit in the world as it does not require anything except LDR. We cannot say it as a circuit as it does not require anything.
D) Now joint the two circuits which you have made.
E) Fix the LED and LDR both in the parallel. But opposite to each other.
F) You can see in this that we have made a relay in which only one current is passing means that it is one directional.
G) This circuit is only based upon the current flowing capacity of LDR.
We here observe that it is that circuit which draws very less energy and gives out current in only one direction. But we need relay which should be connected not the other end if the signal is not coming. For that we will need the help of magnetic field.
1. See that the LED and LDR are in the same line.
2. The battery should be connecting well.
3. Connecting wire should be tightly wind.
Relay as a switch
We require something that can make a relay to switch on another circuit when signal is not coming.
1. Take all the material in front of you and then start working on it.
2. First take motor and then attach a wing to it of aluminium if it is not of alluminium then cover it with aluminum foil.
3. Attach a very low power spring to get the restoring torque or force.
4. Attach the motor wire to the signal wire.
5. Attach the wire to the body (note: The wire you are going to attach will be the wire which you are going to attach it with anything. So when using this circuit don’t touch it as high current may flow from it.)
6. Take the 2 plates put it in parallel to each other. As shown in the diagram.
7. Connect the 2 plates in different circuits
8. The wire which is connected with body of the motor will send electricity to the plates.
9. If the signal is coming it will pass electricity to the upper plate.
10. If the signal is not coming it will pass electricity to the lower plate.
We got correct relay which we were searching for. It will gill the current in the direction we want. If you have connected the wire with high volt then don’t touch the body as you may get current.
Project Source Code
Filed Under: Electronic Projects