Circuit Overview

The circuit diagram above shows this project's electronics and wired connections. The two Side Light NeoPixel strips are controlled by an ItsyBitsy nRF52840. Power is provided by a 500 mAh LiPo battery via a LiPoly Backpack which also recharges the battery when power is connected to the Itsy Bitsy board through its USB connector. We'll solder a slide switch to the backpack to make it easy to turn the battery power on and off.

Cut the Side Light NeoPixel Strips

This project uses two 12-pixel lengths of NeoPixel Side Light LED strip. Unlike standard NeoPixel strips, the LEDs on the Side Light strip emit light perpendicular to the strip's surface, allowing a viewer to see the illumination from the LED without having to look directly into a very bright light source.

Identify the segments of strip to cut. You'll need to remove the protective silicone casing around them. The Side Light NeoPixel Strip has pre-soldered power/signal connectors at both ends, but these wires are too bulky to be included in the collar and should not be included in the cut pieces.

When cutting the strip, make the cuts directly across the copper pads - as close to the midline as possible, so that there will be partial pads to solder on both ends.

Solder the Side Light Strips

Solder the output pads of one LED strip to the input of the other. The LED strips sit parallel to each other with outer edges spaced 36mm apart. Place the strips on a flat work surface and align their edges with the largest piece of vinyl as shown, making sure the LEDs on each strip point towards each other. Cut three pieces of hookup wire in the correct lengths to connect the pads.

Read this tutorial for a good overview of LED strip solder techniques. First tin the pads you'll be connecting. Then strip the ends of the wires and tin them with a bit of solder. Once both have been tinned, place the wire end over a pad, and apply a bit of heat with the soldering iron tip until they melt together.

Repeat this step for all three wires, connecting 5V to 5V, GND to GND and Dout to Din. After soldering, slide a small length of shrink tube over each LED strip to cover the solder joints, then heat with a heat gun or hair dryer to shrink the tube and provide strain relief.

Solder the Slide Switch

The LiPoly backpack board has pins designed for attaching a slide switch to control its power output. Before soldering the switch you'll need to sever the trace connecting those pins with a craft knife. We'll only need two of the switch legs, so using tin snips, clip one of the outer legs off of the switch.

Slide the two switch legs through the holes in the LiPoly backpack and solder them in place. Once soldered, you can trim the portions of the switch legs which protrude past the bottom of the board using a pair of snips.

Wire the Backpack

Connect the corresponding Bat, GND and USB pins on the LiPoly backpack and the ItsyBitsy nRF52840 with short lengths of hookup wire as shown. While the LiPoly backpack can be mounted directly on top of the ItsyBitsy with header pins, we want them to sit side-by side in the collar to create lower profile. When joined, the boards should sit approximately 5mm apart.

Its easiest to complete this step by first soldering the Bat wire to both boards. That helps to hold them in position while you solder the GND and USB wire in place.

Connect the ItsyBitsy to the Side Light Strips

Next we'll solder the 5V, GND and Di pads on the strips to the appropriate board pins, leaving approximately 3/4" of space between the ends of the LED strips and the edge of the Itsy Bitsy nRF52840 board..

The LED strip 5V pad connects to the Itsy Bitsy's Vhi pin. From the ItsyBitsy nRF25840 description, we see that the Vhi will always carry the higher of the USB and Battery voltage when they are connected, allowing the NeoPixel strip to run off of either battery or USB power.

In the electronics assembly the Vhi pin is located close to the output end of the upper LED strip, so it will be easiest to connect it to the NeoPixel 5V pad there. Since power and ground on both LED strips are connected to each other, it doesn't matter which strip segment we use to make those connections. Solder a piece of hookup wire to the ItsyBitsy's Vhi pin, but don't solder it to the LED strip just yet.

Next we'll add ground wire. Note that we've already connected the ItsyBitsy's GND pin to the LiPoly backpack, and there isn't another ground pin on the board. We can use a little trick to create a ground connection between the ItsyBitsy nRF52840 and the Side Light NeoPixel Strips without an additional pin. Since ItsyBitsy's microUSB connector is attached to ground through its solder pads, we can solder a ground wire where the microUSB connector meets the board.

Carefully use your soldering iron to place a small blob of solder onto one one of the pads holding the USB connector (shown in the image with the red arrow). Then tin the end of the ground wire and use the tip of the soldering iron to melt the wire to the pad. 

Now solder a slightly longer wire to pin 5 on the ItsyBitsy. This wire will connect to the Di pin on the bottom LED strip. Lay the ItsyBitsy next to the LED strip ends to make sure the wires extend the same distance away from the board. Tin the corresponding pads on the LED strips.

Before soldering the wires to the NeoPixel strips, cut two small pieces of shrink tube and slide them over the LED strip ends. Now solder the 5V, GND and Di wires to their corresponding pads, then slide the shrink tube over the connection and apply heat to shrink it. The final electronics assembly, minus the battery, should look like the last picture at left.

This guide was first published on Feb 02, 2021. It was last updated on Feb 02, 2021.

This page (Assemble the Electronics) was last updated on Apr 10, 2021.

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