Connecting 12v water pumps and switchs

Hi, everyone
First post over here :smiley:
I started looking into Arduino a while back, and today I decided to give it a go, and started doing some planning, but first I would like for someone to double check my connections wich I'm not sure if they are right, project below.

So I'm not sure about:
The relay board GND, where to connect it !?
Connection between the ULN and Relay PCB !?
Pump's connections !?

Parts I'm using:

uln2803a datasheet
relay PCB info

And I think this is all to get me started, if you need more information let me know.


Connect the GND on the Arduino and the relay board together.

You don't need to use the ULN2803 relay driver. The MOSFET on the relay board performs the same function. It turns the small signal from the Arduino into the current needed to drive the relay.

Connect the pump's supply voltage to Cx then connect NOxto the pump. The other side of the pump to the pump's return voltage.
Just like a switch in series with the pump.

You don't need to use the ULN2803 relay driver.

In fact if you do have it then it won't work unless the FET inputs have pull up resistors on them internally, which is doubtful.

Thanks everyone I think I got it, I was using the ULN because a friend of mine told me, but in his case he was using independent relays with no MOSFET. So better for me :smiley:

Richard I based this as the float switch being a normal button is this right ?

What do you mean "Turn on the internal pull-up resistor for this pin" do that on the programming later? this would be easyer, no need to use a resistor outside right :slight_smile:

Fixed the 2nd pump connection to NO.

Some digital PINs are reserved for the keypad and LCD shield but im leaving that for later.

Please check my schematics now.

Thanks you guys bend very helpful.

Hi, Richard, exactlly I might get a 5A 12v power supply and use it for both pumps and Relay's :slight_smile:

Also I might need to turn off/on 2x 220v pumps I did some calculation and:

1ยบ pump 33w, 150mA
2ยบ pump 66W, 300mA

I checked that the relay's support up to 10A/230AC so this shouldnt be a problem!?

Glad I'm finally get a hang of this :slight_smile: :slight_smile:


perfect thanks.

Will rest for today.