Grab one of the female connectors you cut from the end of your LED strand. It has 5 wires: two loose power and ground wires and the three that were connected to the lights.

Solder your male battery connector to the two longer loose power wires: red to red, and black to the other.

On your QT Py, solder a red wire to 5v, a black wire to G, and a white wire to A0. Connect these wires to your connector's remaining 3 wires: red to red, white to the middle wire, and black to the remaining wire.

Test It

Now, plug in your battery and one of your light strands to be sure your wiring is correct and your software is working. If everything looks good, it's time to seal it all up. If you don't see any lights, head to the Troubleshooting section below.

Once you're sure everything is working, cover your QT Py in heat shrink to help keep the wire connections from flexing and breaking or pulling out.

Add your on/off switch by soldering it in-line with the red wire on your power connector. I added a zip-tie for strain relief to help make sure these wires don't break or get pulled out.


If your lights don't work when you plug in your battery, here are a few things to check:

If your lights don't come on at all:

  1. Check all your wire connections against the wiring diagram to be sure everything is wired correctly.
  2. Be sure your battery is charged, and that the wires on the top haven't come loose.
  3. Check to be sure you're connected to the IN end of the LED strip and not the OUT end. It won't work if you connect them the wrong way.
  4. Visit http://mermaid.local/ in your web browser (or whatever URL you set up during software install.) Didn't set one up? Go back to and plug your board in, and click "Install" again. If your software installed correctly, it will lead you back to your controller.
  5. Did you remember to change the GPIO pin number in the WLED software, on the LED Seup page? Pin A0 on the QT Py is digital pin 26, so be sure you've updated that.

If your lights come on in yellow, but you can't control them:

  1. Make sure you're on the correct Wifi network. Your device needs to be on the same network as your lights.
  2. Try reinstalling the software from If your board is recognized, the installer will take you back where you need to be.

This guide was first published on Nov 02, 2022. It was last updated on Mar 08, 2024.

This page (Electronics Assembly) was last updated on Mar 08, 2024.

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