Solder the headers to the top / front of the QT Py. The easiest way to do this is to place the headers into a solderless breadboard with the short ends up, and set the QT Py on top upside-down, so you're soldering to the back of the board.
The QT Py will plug in to the female headers on bottom of the BFF. Be sure the USB port on the QT Py is aligned with the 2.1mm jack. Double check that the pins are lining up correctly -- it's easy to mix this up and you can damage your board if you plug it in backwards.
If you're new to header usage, check out our guide on how to solder headers.
Cut your Stemma connector in half and strip some shielding from the yellow wire. Slip a piece of heat shrink on there.
The light strand has 3 wires: power, ground, and data. The data wire is directional: solder to the IN end and not the OUT end or it won't work.
My lights were helpfully labeled at the factory, but not all lights from all sources will be labeled, and they aren't always standardized. The only way to be sure you're getting it right is to test.
Alligator clips can be very helpful here -- make your connections temporarily and be sure everything works before your solder.
Testing is a little tricky here. We can't just hook the clips to a Circuit Playground Express running known good code, since these lights require 12v power. So we'll need to test with our QT Py and BFF setup.
Connect the red and black alligator clips to wires coming from the screw terminal or 2.1mm jack on the BFF, and the data wire clip to the yellow wire on the stemma. If your lights don't come on, try connecting JUST the data wire to the other end of the strand.
Once I'd figured out which wire was which, I added some color-coding by soldering a red wire to the power (striped) wire on the connector, a yellow wire to the middle (data) wire, and a black wire to the remaining (g) wire. This way, it was easy to keep the wires straight once I got them inside the box.
If your power supply has a 2.1mm or other jack, cut it off. Thread the wires through one of the cable glands from the outside so the bare wire is inside the box.
Slip the 3 wires from your light strand's extra connector through the other cable gland. I attached a female connector to the box, since my IN end on my lights has a male connector.
Connect all the power wires to the BFF, using either the reconnected 2.1mm jack, or a male 2.1mm screw terminal, or the included screw terminals. It doesn't matter which way you connect the wires, just be sure both red wires are going to + and both black wires are going to -.
Splice the third (middle) wire from your connector to the yellow wire from the Stemma connector and plug it into the QT Py, then plug the QT Py into the BFF.
All wires accounted for? Double check once more that reds are going to + and blacks are going to -, then plug in your light strand and your power supply to light up your strand.
Splice the third (middle) wire from your connector to the yellow wire from the stemma connector and plug it into the QT Py, then plug the QT Py into the BFF.
All wires accounted for? Double check once more that reds are going to + and blacks are going to -, then plug in your light strand and your power supply to light up your strand.
Troubleshooting
If your lights don't come on or act strangely, here are some things to try:
- Try connecting the data wire to the other end of the strand. The data wire on these lights are directional.
- Be sure your screw terminal connections are tight and haven't pulled out. Add some zip ties to either side of the cable gland to act as strain relief.
- Be sure you've uploaded the code successfully, and that the correct data pin is specified.
- If your lights are on but the colors are unexpected, try changing the color order in the code. Look for a line that shows BRG, RGB, GRB, etc and just mix the letters up and re-upload. This tells the code to look for Blue, then Red, then Green (or whatever order you've specified). This isn't really standardized so can cause the colors to come out wrong.
- Flickering? Try a different power supply.
- One light comes on? Your power and ground wires may be reversed.
Once it's all working, tighten the cable glands and close up the box with the included screws. I added some industrial velcro to stick my box to my power supply, and put zip ties on the inside and outside of the cable glands to add additional strain relief.
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