Published May 8, 2025 © GPL3+

Open Hardware Summit Badge 2025

A tutorial for how to assemble your OHS 2025 E-Textile Badge

Story

This project is a step-by-step guide for assembling the 2025 Open Hardware Summit badge. It's also a friendly introduction to e-textiles, covering circuit layout and showing how to sew electronic components onto fabric

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The Circuit

These badges are made up of four components: a Xiao ESP32 microcontroller, two WS2812B-2020 addressable LEDs, and a female SAO connector. You can program the microcontroller to control the LEDs and interface with an SAO board through the header. At the time of writing, the SAO connector is still in production, so it's not pictured in the tutorial. The traces in this diagram are color coded as follows:

Color: Label [MCU Pin]

Red: +5v [5v]

Blue: Ground [Gnd]

Green: LED Data [D7]

Yellow: SCL [D5]

Purple: SDA [D4]

Cyan: GPIO2 [D2]

Orange: GPIO1 [D1]

CAD View

The badge may be powered by USB directly to the microcontroller or by sewing a textile battery to the terminal in the top right corner.

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Assembly

Before you sew components you must trim thread tails left in the manufacturing process. Why did I not trim the thread as it stitches? Machine cuts of conductive thread add a significant amount of machine time to manufacturing and increase the chance of QC issues. Each stop and start leaves a conductive bird's nest on the underside of the fabric. Jumping from trace to trace helps minimize this. You will have to trim each jump of conductive thread on the front and the back of the badge. A clean cut is less likely to short later. The trim locations are shown in the following image.

1 / 2 • Thread jumps must be trimmed

To assemble this badge requires sewing instead of soldering. The components are laid on top of the embroidered traces, and their pins are sewn in using conductive thread. The images below show LEDs sewn into conductive traces. Observe how we are laying the PCB over the existing electrical traces. From there, we sew the PCB into the traces through it's contact holes. This should give you an idea of what the goal is with sewing each of the components. Please excuse my poor hand stitching.

1 / 2 • Hand Sewn

Tips:

Loop into the PCB hole 4+ times. Use more loops if necessary
Make the loops as tight as possible
Make sure you have physical contact between the pre-sewn trace, the thread you are sewing, and the exposed "pin" of the LED
Trim any fraying or stray strands of conductive thread

Use this image as a reference for component orientation. Look out for the LEDs in particular. Notice that the marker on the lower LED faces up and the marker on the upper LED faces the left.

Component Orientation

Power

As mentioned earlier, you may power the badge via USB but most people would probably consider that overkill for the badge. We will implement a non-standard hacky solution. We will stack coin cell batteries, until it works. Why this method instead of a plastic coin cell holder or lipo connector? It minimizes time and HW components. The coin cell batteries will be housed inside of a small tag made to attach to the terminals at the top right of the badge. Below is a front and back image of the tag prior to being sewn. You will have to trim the thread between the terminals on both sides of the battery pack and also trim any stray threads left from manufacturing. Stray thread on the backside of a normal embroidery is no problem but with conductive thread, they cause shorts.

Blue: Design Trims - Yellow: Stray Thread

After trimming, fold the battery pack in half with the paper interfacing facing outwards and sew along the Black guide line. That line is a minimum. You may move the line to make more space in the battery tag. The following images show a sewn battery pack with a coin cell battery inside. Look closely and you will see that I sewed beyond the guide line because I wanted to use 3 coin cell batteries.

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Attach the battery to the rear side of the badge. Polarity is important here. For the battery pack, it has 2 pads. One is larger than the other. The larger pad pad is positive. When the battery is inserted into the pack the flat side of the battery should be touching the large positive pad of the pack. The pictures above and below show this. Be sure that you sew the positive terminal of the battery to the positive terminal of the badge.

Large Battery Pad Faces You - Small battery Pad Faces Badge

Gallery

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Example Blinky

#include <Adafruit_NeoPixel.h>

// LED setup
#define LED_PIN    D7     // Data pin
#define LED_COUNT  2
#define BRIGHTNESS 100

Adafruit_NeoPixel leds(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);

// SAO pin macros
#define SAO_PWR     D5
#define SAO_GND     D4
#define SAO_GPIO2   D2
#define SAO_GPIO1   D1

void setup() {
  leds.begin();
  leds.setBrightness(BRIGHTNESS);
  leds.show(); // Clear all LEDs
}

void loop() {
  setAll(255, 0, 0);   // First channel full
  delay(1000);

  setAll(0, 255, 0);   // Second channel full
  delay(1000);

  setAll(0, 0, 255);   // Third channel full
  delay(1000);
}

void setAll(uint8_t a, uint8_t b, uint8_t c) {
  for (int i = 0; i < LED_COUNT; i++) {
    leds.setPixelColor(i, leds.Color(a, b, c));
  }
  leds.show();
}

Credits

Rodney Trusty

2 projects • 12 followers

Anomaly

Open Hardware Summit Badge 2025