Prep LED Strips

Now we need to convert these 5-meter reels into 2-meter strips for hanging. Each reel provides two 2-meter strips, plus one 1-meter strip. The latter can be joined in pairs to produce a few additional 2-meter lengths.
Peel back the rubber weatherproofing cap on the end of the strip (you might need to cut or tear it away…that’s okay, we won’t be needing it). Then cut the wires, close to the strip.
Using a soldering iron, scrape the remaining wire tips off the solder pads.

Be super extra careful to avoid getting any tiny wire strands or solder balls down inside the sleeve! Also watch out for solder bridges between the pads.

There may be little bits of rubber stuck here and there. Peel them away with tweezers, or scrape them with the iron if they’re on the solder pads.
Unroll the strip and repeat for the connector at the opposite end. We won’t be using the JST plugs for this project, but save them for future things…they’re quite handy!

NeoPixel strips are all manufactured in half-meter lengths. These are joined at the factory to produce a complete reel. If you look along the strip, you can clearly see where the sections are joined…there are solder connections there.

Measure 2 meters down the strip. Or simply count four half-meter sections.
Using a hobby knife or box cutter, carefully cut through the sleeve (but not the strip) at the 2m mark, where the solder blobs are.
Separate the strip using a soldering iron.

Normally you have to heat the three pads and gently twist the strip away (it may take several passes). Or if you’re lucky, you have an iron that they make these extra-wide tips for.

As with the end of the strip, watch out for solder balls and bridged pads.
Measure, cut and desolder a second 2m length of strip. You should then have a 1m section left over.
Repeat for all of the NeoPixel reels.

Later steps will be easier and less error-prone if all of the strips (both the 2m and 1m varieties) are laid out flat, all oriented the same way. Don’t leave them in a heap of disarray.

Joining the 1m Sections

Working with 10 reels of NeoPixels, there’s now 20 two-meter strips and 10 one-meter strips. The latter will be reconnected into 5 two-meter strips, for 25 two-meter strips total. 24 will be assembled into the curtain, one is left over as a spare (for future repairs). With better planning I’d have allowed for a few additional spares!
It’s extremely important that the two sections are straight. Even a tiny kink will throw off the whole grid!

A straightedge is used as an alignment guide; this and the LED strip are taped down to the work surface.

Make sure you’re connecting DOUT to DIN. Don’t join strips back-to-back!
The end of one strip overlaps the start of the next (one set of pads should be directly over the other) and the connections are re-soldered.

These strips are going to see a lot of abuse, and the solder connections better be bulletproof! If you’re having trouble successfully re-joining strips, you may need to remove the old solder from the pads (using solder wick) and start fresh. Old solder gets weird and sticky when all the flux has boiled away.
Check for shorts between pads using a multimeter. This strip looked great on top…but it turns out all three pads were bridged underneath! Clean these up with the soldering iron and some solder wick if needed. And once again, watch out for solder balls getting into the sleeve.
Later we’ll seal the gap in the sleeve…but not yet. It’s prudent to test all the strips before making those connections inaccessible.

Adding Wires

We’ll now add JST plugs to each strip. Wait…didn’t we just remove a bunch of JST plugs?
These are different. They’re three-pin connectors, to match the three pads on the NeoPixel strip. And there’s one for every 2m strip (at least 24, plus any spares).

Using plugs (rather than hard-wiring the strips) makes maintenance much easier, if any strips need replacing later.

IMPORTANT: Set the female (socket) receptacles aside for later, use male (pin) plugs on the strips. This is the opposite of the factory connectors, but it’s safer (sticky-outy things on the power supply side is a bad idea).
The rubber sleeve is cinched back a bit and clamped in place, then the wires from the JST plug are soldered to the strip. (In hindsight, I might’ve cut these to half their original length and stripped new ends…but your overall design might be different.)

JST plugs feature a polarity “key” so they don’t plug in backwards. Doesn’t matter which orientation you choose, just make sure every plug/strip is aligned the same way!
Make sure you’re connecting to the DIN end.
Like the joined strips, these solder connections are going to see a lot of abuse, so you’d better have some Nobel Prize-worthy solder connections, shiny and flowing smoothly between the copper pads and the wires.
Not too much, not too little, and not “balled up” on the surface. It may work best to wick off any old solder and apply fresh.

And you know the drill by now: don’t let any solder bits get down inside the sleeve.
Repeat this for all 24 strips plus the spares. When you’re done, check these things on every strip:

  1. Are all the JST plugs oriented the same way on every strip? With the “key” facing either up or down? Doesn’t matter which way, just be consistent.
  2. Did you connect to the DIN end?
  3. Use a multimeter to test for electrical shorts: GND to DIN, DIN to +5V, and GND to +5V.
  4. For the joined strips, confirm DOUT connects to DIN; arrows should point the same way down the whole strip.
Do not continue until every strip checks out!

Test Again

Sorry for the repetition, but it’s really important.

Return to the Arduino code that was used for testing reels, and make one small change near the top:
Download: file
#define N_LEDS 60 // 2 meter strip @ 30 LEDs/m
Upload this modified code to the Arduino, then disconnect the USB cable.

Take one of the mating JST receptacles (female socket) and strip a little extra insulation from the wires. Plug it into one of the strips and trace the wires so you know exactly which is +5V, GND and DIN. Double check, then maybe even stick labels on them.

Connect the wires to the corresponding points on the Arduino: 5V, GND and pin 6. If possible, route DIN through a static-protection circuit as shown on the prior page.

Re-connect the USB cable. You should get the LED “chase” again, red, green and blue. Let it run for a couple minutes as you examine the entire length of the strip. If everything checks out, unplug USB first, then the JST connector, then reverse these steps as you connect the next strip for testing (we’re avoiding connecting the strips to a live circuit).

Troubleshooting is about the same as for reels. If there’s a problem, stop immediately and refer to the checklists on the prior page, and also look for the following:

  • Confirm that 5V, GND and DIN are properly routed from the strip, through the JST connectors, to the Arduino.
  • Confirm you’ve soldered the plug to the DIN end.
  • Confirm all the JST plugs are oriented the same way. You can have all the “keys” on the NeoPixel side of the strip, or all on the back, but not a mix of the two.
  • For joined strips, confirm you’ve soldered them DOUT to DIN (arrows all pointing the same way), not back-to-back.

Sealing the Gaps

Do not continue until every strip has been tested. Going forward, all those solder connections become inaccessible…if something was mis-wired, it might not be salvageable after this.

Set aside all the full 2m strips. This next part applies only to the joined (2X 1m) strips.

Lets fix those gaps in the sleeve, where the two pieces meet…
Cut some 1-inch sections of clear heat-shrink tube (1/2" diameter). Slide one over the strip…close to, but not yet on top of, the gap.

Wriggle the sleeves so the ends butt together close to the solder connection. You may need to hold the end of the strip with pliers and “inchworm” the sleeve down a few millimeters over several passes.

Squeeze some hot-melt glue or Permatex 66B under both sleeves, top and bottom (tested both…hot glue is cleaner). Re-butt them, slide the tubing over the gap and shrink it using a heat gun.

You really need to use a heat gun for this. Flame does not work well on large heat-shrink, and may be unsafe for certain glues!
It’s not beautiful…but with the LEDs turned on, and from a couple feet away, nobody will notice.

Aside from weatherproofing, the glue + heat shrink provide some much-needed strain relief for the solder connections.
This guide was first published on Aug 11, 2014. It was last updated on Aug 11, 2014. This page (Prep LED Strips) was last updated on May 04, 2015.