Bling out your swag with 3d printed LED knuckle jewelry. Its stylin’ to make this bright and blingy project!

3d print yourself a fully assembled chain for a more casual approach. You can easily show ASCII characters or scroll messages to make custom tags.
You'll need a few tools and parts to get this project lit up.


Tools & Supplies


This design was printed on a Printrbot in transparent yellow PLA filament. The tolerances are optimized for PLA, but should print well in ABS.
Easily switch out the design to either a chain necklace or knuckles, just swap out the lid of the enclosure!
Supports for:

No raft or support for:
ABS/PLA @240
10% Infill
2 Shells
0.2 Layer height
3 hours for all fours pieces 
Measure your middle and ring finger for a nice fit around your fist. The clips that hold onto the lid will require supports.


Print with the face down, the slide switch hole will require supports.

This lid connects to the knuckleBox.stl via the knuckle-lidClip.stl


Insert into the knuckleBoxLID.stl and slide the connected parts into the knuckle.stl clips.
The illustration above is a reference of the wire connections. The slide switch adapter allows the circuit to be easily turned on.
  • Vi2c pin to 3V or 5V pin (depending on which trinket you use)
  • VCC pin to Trinket BAT+ pin
  • SDA to Trinket #0
  • SCL to Trinket #2
  • GND to GND
Get more code examples on our github: Adafruit-LED-Backpack-Library
#include <avr/power.h>
#include <TinyWireM.h>
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"

Adafruit_AlphaNum4 alpha4 = Adafruit_AlphaNum4();

char *message = "**3D** 4 LIFE***    ";

void setup() {
  if (F_CPU == 16000000) clock_prescale_set(clock_div_1);
  alpha4.begin(0x70);  // pass in the address
  alpha4.writeDisplay();  // clear display

void loop() {
  // just display 4 letters
  alpha4.writeDigitAscii(0, 'H');
  alpha4.writeDigitAscii(1, 'A');
  alpha4.writeDigitAscii(2, 'C');
  alpha4.writeDigitAscii(3, 'K');
  delay(1000); // hold for 1 second

  // scroll the message above!
  for (uint8_t i=0; i<strlen(message)-4; i++) {
    alpha4.writeDigitAscii(0, message[i]);
    alpha4.writeDigitAscii(1, message[i+1]);
    alpha4.writeDigitAscii(2, message[i+2]);
    alpha4.writeDigitAscii(3, message[i+3]);

Assemble 14-Segment LED

The Quad Alphanumeric Display comes with a backpack that you will need to solder together. Follow the guide to complete this assembly.

Soldering Assistant

Use a third-helping hand and Panavise to assist you while you solder.

Clip Pins

The access pins can cause the circuit to be too large to fit into the enclosure so you'll need to trim these. Use flush diagonal cutters to clip off the pins from the back.

Wire Connections

Measure and cut 4 strands of wire wrap to about 20mm in length. Solder these wires to SCL, SDA, GND, VCC and Vi2c pins on the 14-segment LED Backpack.

Slide Switch

Build an on and off switch by measuring a JST Extension cable and splicing the positive wire between the slide switch. We'll need it to be as small as possible, so cut off the pin and solder the wires to the small nub that's left over.

Heat Shrink

Use heat shrink tubing to secure the spliced ground wire connections. These little slide switch come in handy in many projects, so it's a great idea to make extra!

Solder JST connetor to Trinket

You'll need to solder on a female JST connector to the back of Trinket . This will connect to the male JST connector of the slide switch.

Wire Trinket

Use a panovise jr. or third-helping hand to secure the backpack in place. Lay the trinket over the backpack and thread the wires through the corresponding pins.

Solder Connections

Ensure the wires are long enough so that the Trinket has enough room to plug a USB cable in for reprogramming.

Solder wires as listed below:
#0 to SDA
#2 to SCL
VCC to VBat
Vi2c to 5v / 3v

Install into Enclosure

Plug in the slide switch circuit, align and carefully slide the completed circuit into knuckleBox.stl. Once the 7-segment display fits through the opening, grip the edges the pull the rest the the circuit.

Fit into place

If the tolerance is too tight, use an x-acto knife to enlarge the opening.

Install Slide Switch

Position the slide switch into the the opening and push it through.

Adjust Wires in Enclosure

Curve the JST extension around the inside of knuckleBox.stl.

Install Battery

Plug in the 110mAh battery. Curve the wire to fit it inside the box.

Prepare Enclosure Lid

Position the knuckle-lidClip.stl over the knuckleBoxLID.stl part.

Secure Lid

Snap in knuckle-lidClip.stl into knuckleBoxLID.stl.

Install Knuckles

Slide the knuckle-lidClip.stl nub in between the clips on knuckle.stl.

Right-side Up

The rings should have a comfortable fit, not too tight or loose. Ensure the parts are positioned with the 7-segment display facing the correct orientation.

Chain Customizer App

Included is a chain that prints fully assembled in place. The knuckle-lidHoop.stl part was created by the chain generator customizer app available on thingiverse.

Wear it!

Show of your bling bling in your latest music video and be sure to share it with us!

This guide was first published on Jun 23, 2014. It was last updated on 2014-06-23 22:51:41 -0400.