Control 12V components with Arduino and Relay (newbie)

So first of all, I'm pretty new to this Arduino and electronic world..

The thing is, that I want to control some components (compressor and solenoid valves, all 12V) with an Arduino and a 8-channel relay.

I found this picture for connecting:

But I'm confused, because some other pictures doesn't connect the GND from the relay to the GND on Arduino.

The Arduino should only control the Relay ON/OFF.


Please give us a link to the actual relay card you are going to use.


It maybe this one.

dlloyd’s drawing


Details, diagrams about this subject HERE

NEXT thing is Solenoids etc. Can be ElectroMagnetic Interference territory.

Some help HERE

The relay I'm going to use:

But I bought mine from a Danish website, not Aliexpress :slight_smile:

The picture shows a 5V supply and I guess I'm gonna need a 12V supply?

If the relay coils are 12vdc, you will need an external 12 volt supply.
If they are 5vdc you will need an external 5 volt supply.

What is written on your relays?
SRD ? ? ?


On the relay It's written 10A 250 VAC, 10A 125VAC and 10A 30VDC, 10A 28VDC.. But since all my components (compressor etc) is 12V DC, I guess im gonna need at 12V supply?

"On the relay It’s written 10A 250 VAC, 10A 125VAC and 10A 30VDC, 10A 28VDC… "
That sounds more like the load the contacts can switch. 10A at the different AC & DC voltages.

What is being asked has to do with the voltage needed across the coil to energize the coil and switch the contacts.
Can be 5V, 12V, 24 - which is it?

Yes, as Crossroads says.

What is written after:


Oh sorry guys, It says SRD-05VDC-SL-C

Those are 5 volt coil relays.

They take 5 VDC to energize the relay, 'NOT' 12VDC.
You will need an external 5 VDC supply.
Do not use the Arduino 5 volts.


So I need a 5V power Supply for the relay and a 12V power supply for the components?