Power 5V Relay direct from 5V Source

Hey All,

Relatively new to electronics and managed to get the 5V relay working with Arduino which is fantastic.

However I’m wondering why I can’t get my 5V relay to work direct from power source.

The voltage drop across the Input is 5V, similar to Arduino output, yet the relay won’t engage and I can’t figure out why.

I’ve attached a diagram which shows how I’ve wired it up.

Relay Diagram.jpg

How to attach an image

Here's OP's pic:

Relay Diagram.jpg

Looks like you have a relay module (ie relay on a board) not a bare relay? Most of those are active low, gnd to in.

(But that wouldn't explain how your code's working, unless you're digitalWrite()-ing a low there too.)


Yes you're correct, it's a module - not just the relay itself.

There's no code - I'd just like to wire it up directly to the power supply and a reed switch.

I'll try using ground....

There's no code

I saw this:

managed to get the 5V relay working with Arduino

... and took that to mean a code solution.

Yep that worked, thank-you so much.

So I need to use GROUND instead of the 5V supply to activate the relay module.


Keen Nosey to know why you have an Arduino in the mix if it's not for its program...

I did post it in "General Electronics" :slight_smile:

I'm just wanting to use a simple Reed Switch to activate a relay - not really arduino related.

Thank-you for your assistance.

Arduino-as-power-supply :wink: