A relayboard is effectively a board containing one or more relay switches. A relay switch is often used to switch a large amount of power on for a small operating energy; or to turn specific circuits on and off within an application.
Often the relay becomes the breaker point between a low and high voltage, or a low and high current, part of an application. The most obvious version of this usage is the RCD board used to insulate your home against electrical surges. The trip switches on the board are all relays – in effect making the RCD (otherwise known as a residual current device) one of the largest and most obvious relay boards in the country.
This form of relay usage is referred to as circuit breaking.
A relay board may also be used to instil Boolean logic functions into the workings of a device. The open and closed states of the relays are used to signify AND, OR, NAND, or NOR. The AND function is created when two normally open contacts are connected in parallel. NAND and NOR functions have similar connection protocols, but with normally closed switches.
The switches in relay boards are categories either as NO or NC (normally open, or normally closed). Thiscategorisationrefers to the natural state of the switch – in other words its “resting” position. A switch that rests “closed” will be passing current in its supine state; and, when activated, will turn the current off. A switch that is normally open will pass no current in a state of rest – but when activated, will complete a circuit.
To use relay boards properly within applications, then, a number of considerations must first be made. The number and style of contacts required is your first consideration – how many normally open or normally closed switches do you need to provide the functionality required? There is, by the way, a third type of switch to throw in to the mix – a double throw switch, which has no normally open or closed designation.
You have to think about the end purpose of your application in order to define the contact sequence correctly. For instance, a make before break circuit is required if you are relaying an audio signal, otherwise you drop the audio connection when you activate the relay. This kind of contact sequence was used in telephone relays to prevent the caller from being dropped as the number was dialled.
The useful life of your relay board is another prime consideration. Relay boards are part of electrical circuits, but they have mechanical parts too – which means they have a reasonably easy to define lifespan. It goes without saying that you need your relay to be capable of flipping at least as many times as the lifetime of the application demands, if not more.
The material you use at the contact point is also key. In situations where your device requires low voltages to be switched, the contacts for relay boards may need to be coated in special material such as gold plate.