Use Duex5 to get 12v

As far as I know the Duex5 (also in Duex2) is the only Controller or Expansions -board for 3D Printers with build-in 12v switching regulator, which means you can easily get 12v even if you use a higher voltage to power your machine (VIN Power - opens Duet3d Glossary) without having to resort to various step-down modules lying around in or outside your printer creating risks for shorts and other errors.

Jumper Settings

In order to activate this 12v switching we need to:

Put a jumper on the pins marked with nr. 1
Check the FAN jumper nr. 2 is placed on the 12v position
I'm going to use the FAN3 Connector marked with nr. 3 for my LEDs

In case you have difficulty seeing the colors as me, being colorblind, the + wire is to the right side of the 2-pin connector, and - wire on the left side.

The diagram I've created is created from the original conenctions diagram on Duet3D wiki.

Step 1: Configure Firmware and Customization Options

Configure firmware

We really just need to open the Config.g file and insert a small line under the other fans in our FAN section, like this:

M106 P3 S1; Set fan 3 value for our LED to on.

It really just put FAN connector 3 on full power.

Further customization options

We can put the power to the LEDs on half (dimming it) by setting S to 0.5 instead of 1, or use the 0-255 range if that's more to your liking.

It also means you can control it using Gcodes to do different things like turning LED on when a print starts and turn it off when a print job ends or what ever you like.