The best definition I could find online is:
These handy boards provide a simple method to interface a low level control output from a control system such as the FSR Flex Gpio ports to higher level loads such as a low voltage screen controller. They can also be used to reverse control output logic if necessary
**can someone break this down in layman’s terms?**
In: Technology
Not sure of the exact unit you’re using, but I’ll try for generic relay operations.
As noted by another commenter, a relay is just a form of switch. Your car has a multitude of relays, which are used to avoid high amperage circuits from being run into the switches in the car.
Example – headlights…a car’s headlights can draw between 8-10 amps (highbeams on older vehicles). That sort of load would require a heavy gauge wire to operate. It is inconvenient and unsafe to try and route a heavy wire from the fuse block all the way to the switch and then back out to the headlights – especially if the switch is on the turn signal lever.
Instead, they run a small gauge wire through the switch, which only needs to carry a load of about 0.02 amps – this circuit will operate a small electromagnetic coil inside the relay. When that coil is activated, it closes a set of spring loaded contacts inside the relay. These contacts are what carries the higher amperage load of the lights. The relay can be mounted under the hood, between the battery and lights – much shorter run heavy wire.
Standard “Bosch style” relays will also have numbers to designate the terminals:
85 – power to electromagnetic coil
86 – ground for coil
30 – power for heavy load
87 – power to heavy load (normally open contact, only sends power when coil activated)
87a – power to heavy load (normally closed contact, only sends power when coil deactivated)
Just to confuse things, some controllers don’t send power to the coil, but instead activate the ground side of it.
Do a search for something like “fog light relay circuit” for visual examples.
We also use relays in industrial applications – can use a 24VDC signal to activate the coil, while the heavy load may be a 480VAC circuit.
A relay is a physical switch that is controlled by an electric current. So a relay have two different sides to it. There is the control side and there is the switched side. The control side have two pins while the switched side typically have three pins but can have a different number of pins depending on what kind of switch it uses. The relay is used to seperate two circuits from each other. As there is no electronic connections between the controll side and the switched side nothing on the switched side can affect the signals on the controll side. The circuit is galvanically seperated. That is of course assuming you stay within the limits for voltage and current of the relay.
Relays are often used in control circuits to allow a low current low voltage signal control a high current high voltage load. For example the GPIO pins on a microcontroler might not output enough voltage or current to power motors, heaters, lights, etc. However they might have enough output for a relay which can then switch the load on or off. For example you can apply a 3.3V 100mA signal on the control side to switch on a 24V 5A light on the other side of the relay. It is also possible to use the relay the other way around, having a high voltage signal power the relay to give a low voltage signal to the microcontroller. This is an alternative to a voltage divider or an optoisolator but offers greater degree of isolation so you are guaranteed that the high voltage never reaches your microcontroller.
Relays are just switches. You can make them change state when inputs change or switch a voltage from a power supply separate to your main card.
Please and thanks. I just bought a kit and am about to assemble a relay board… but I don’t know what I can use it for when it’s complete.
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