Solder your 3-pin female connector to the QT Py as shown:
- Right wire to 5v
- Middle wire to A1
- Left wire to G
This will attach to the NeoPixel strip.
Solder your 2-pin female connector to pins A2 and A3. These pins will connect to the capacitive touch wires we're using as a mode controller and an on/off switch.
Find the "in" end of your NeoPixel strip - it's the end with the little arrows pointing away. Our microcontroller needs to be connected to this end for the pixels to work.
Solder the male side of your 3-pin connector to the red, black, and white wires. It's helpful to plug the two halves of the connectors together before you solder so you can be sure which wire is connecting to which pin.
Be sure the red wire connects through both halves of the connector to 5v, the white wire to A1, and the black wire to G.
If you've already uploaded your code, plug in your QT Py with a USB cable and test to be sure your lights come on.
Solder a long wire to each pin of your male 2-pin connector. These wires will need to be long enough to reach your copper tape "switch" pads so give yourself a little extra wire. You can trim them down later.
Plug the 2-pin connector in to the QT Py. Strip some shielding from the far end of the wire and pinch it with your fingers to make the light strip change color modes (A2) or turn on and off (A3).
Waterproofing
Next we'll add the submersible NeoPixel strand. These lights are really sturdily made and can happily be used underwater, but you will need to seal both ends if you want to submerse the entire strand.
First we'll seal the "out" end completely, then we'll add a waterproof extension wire to the "in" end, so we can run the extension up the back of the tank to connect with the above-water NeoPixel strip.
Find the "out" end of your NeoPixel dot strand. On my strand it was the end with the female connector, but always double check the arrows on the back of the strip in case the strip you have has the connectors assembled differently.
Cut this connector off. Cut a piece of clear heat shrink tubing and slide it over the exposed wires.
Fill the end of the heat shrink with hot glue. While the glue is wet and molten, grab your heat gun and shrink the heat shrink, being sure the end of the strands are fully enclosed. This will encase the end of the strand in plastic and completely waterproof it.
Take the female connector you cut off (from the out end of the dot strand). Splice it onto the out end of your LED strip. Connect the red wire to the red-striped wire on the connector, the white wire to the middle wire, and the black wire to the remaining wire.
This connector will be above the waterline, so you don't need to worry about getting the connections water-tight.
Plug in your NeoPixel dot strand and test to be sure your lights come on.
If you want the strand of lights to be visible running down the back wall of your aquarium, you can stop here and start putting your aquarium together. Just keep the connector above the waterline and drop the rest of the strand into the water.
I want my entire light strand to be submersed, without any lights along the back wall. To achieve this, there's one more step: adding a waterproofed extension wire to the in end of the NeoPixel strand, long enough to reach the bottom of the tank so I can bury the entire light strand under the gravel.
I'm using solder seal connectors with silicone stranded wire to make the underwater connections waterproof. A Solder seal connector is a piece of heat shrink that contains some low-melt solder and a couple of glue seals on either side. A heat gun will melt the solder and the glue, creating a submersible solder connection in just one step.
These work great for underwater connections or for in-place repairs on your project, but they are a bit more likely to cause a cold solder joint than a good connection made with a soldering iron. If your project needs to flex or move a lot or needs to pass a lot of current, stick with traditional soldering and heat shrink with glue. But for small projects that don't need to flex, these can save you a lot of time.
And of course, if you don't have any of these on-hand, you can also use the same hot-glue-and-heat-shrink method detailed above over all three solder joints.
For the wire, I'm using 4-stranded 26awg silicone ribbon cable. Silicone stranded wire has a completely waterproof silicone shielding, which will never absorb water or get waterlogged. Choice of wire is important here - cheaper plastic-shielded wire really won't work as well for an underwater connection as the water will eventually seep through the plastic.
Find the striped wire - it's on one edge of your 4-wire strand. Grab the wire on the opposite edge of your ribbon cable and remove it completely, so you're left with 3 wires, one of which is striped.
Separate the ends for a few inches and slip on your solder seal connectors.
Cut the connector off the in end of your NeoPixel dot strand. Twist the ribbon cable onto the ends securely: striped wire to red striped wire, middle wire to middle wire, and remaining wire to remaining wire.
Slide the solder seal connectors over your twisted wires so the gray ring in the middle is positioned right over the exposed wires. Heat the connectors for 20-30 seconds until the metal liquefies and the glue rings on either side have melted completely.
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