Relays:
The relay takes advantage of the fact that when electricity flows through a coil, it becomes an electromagnet. The electromagnetic coil attracts a steel plate, which is attached to a switch. So the switch's motion (ON and OFF) is controlled by the current flowing to the coil, or not, respectively.
A very useful feature of a relay is that it can be used to electrically isolate different parts of a circuit. It will allow a low voltage circuit (e.g. 5VDC) to switch the power in a high voltage circuit (e.g. 100 VAC or more).
The relay operates mechanically, so it can not operate at high speed.
There is much kind of relays. You can select one according to your needs.
The various things to consider when selecting a relay are its size, voltage and current capacity of the contact points, drive voltage, impedance, number of contacts, resistance of the contacts, etc.
The resistance voltage of the contacts is the maximum voltage that can be conducted at the point of contact in the switch. When the maximum is exceeded, the contacts will spark and melt, sometimes fusing together. The relay will fail. The value is printed on the relay.
The various things to consider when selecting a relay are its size, voltage and current capacity of the contact points, drive voltage, impedance, number of contacts, resistance of the contacts, etc.
The resistance voltage of the contacts is the maximum voltage that can be conducted at the point of contact in the switch. When the maximum is exceeded, the contacts will spark and melt, sometimes fusing together. The relay will fail. The value is printed on the relay.
