Cut LED Strip Segments

Most LED strips emit light perpendicular to the strip's surface. The "Side Light" LED strips in this project contain small 4020 (4mm x 2mm) LEDs which project light towards the side of the strip. These kind of strips work well to diffuse light edgewise along a surface into a diffusion material like hot glue.

A single cuff requires two lengths of LED strip containing seven LEDs apiece. You can cut these strips from the reel by snipping directly through the protective silicone coating with flush cutters.

When cutting the strips, be sure to cut through the middle of the solder pads on both strip ends (red arrows in image), leaving a partial pad on both sides of the cut. This allows wires to be soldered to both inputs and outputs of the cut pieces.

Electronics Layout

The wiring for the strips is shown in the Fritzing diagram below. Both LED strips receive power through the QT Py. The QT Py sends the LED control signals into the input of the first strip, and the output from the first LED strip becomes the input for the second LED strip. The strips must be oriented in opposite directions for the signal to travel through both.

The QT Py supplies power to the LED strips from its power pads, and controls the light patterns with a signal from its MOSI pin.

Wire It Up

In order to determine the lengths of hookup wire needed to connect the QT Py and LED strips, lay out the Side Light LED strips and QT Py controller in place on the top foam layer as shown. The end of the QT Py USB connector is even with the end of the foam, and the LED strips sit over the foam with one LED in each rectangular cutout.

Cut appropriate lengths of 26 AWG hookup wire to make the electrical connections. connections. Strip short lengths of insulation from both ends of each wire.

You can connect the power and ground wires to either the QT Py pins or to the small pads on the back of the board. In this tutoral, the wires are soldered to the pads as shown.

Solder the power/ground wires to the power pads and solder the signal wire (green) to the QT Py MOSI pin.

Insulate and reinforce the solder connections by applying a bit of hot glue over the solder joins, then sliding a short length of shrink tubing over the glue. Apply heat to shrink the tubing and hold the connections together.

Place another two pieces of shrink tube over the LED strip ends before soldering the signal wire between them. The signal wire runs from DO of the first strip to DI of the second.

Apply small blobs of hot glue over the newly soldered joins, then slide the shrink tube over the glue. Apply heat to shrink the tubing.

Test the Electronics

At this point, It's a good idea to connect the QT Py to power and run a program, like one from the Adafruit QT Py and NeoPixel tutorial, to be sure all electronics function correctly. If running a demo program, remember to set the LED pin to the QT PY's MOSI pin, e.g.

pixels = neopixel.NeoPixel(board.MOSI, num_pixels, auto_write=False)

This guide was first published on Oct 16, 2020. It was last updated on 2020-10-16 14:35:14 -0400.
This page (Wire the Electronics) was last updated on Oct 16, 2020.