I made a battery powered earing with neopixels. My goal for this assignment was to learn how to use surface mount components so I kept the design and functionality simple.

Schematic and Board Design

Parts List

• WS2812B neopixel (7)
• 0.1μF capacitor (7)
• ATTiny85
• coin cell battery holder
• 3V coin cell battery

Code

I used Adafruit’s example code for neopixels and adapted it for my needs. I turned the brightness down since I’m only powering it with a 3V coin cell battery.

#include <Adafruit_NeoPixel.h>

int pin = 3;
int len = 7;

Adafruit_NeoPixel strip = Adafruit_NeoPixel(len, pin, NEO_GRB+ NEO_KHZ800);

void setup() {
  strip.begin();
  strip.show();
  strip.setBrightness(20);
}

void loop() {
  rainbowCycle(20);
}

/*
  from adafruit's strandtest example
*/

// Slightly different, this makes the rainbow equally distributed throughout
void rainbowCycle(uint8_t wait) {
  uint16_t i, j;

  for(j=0; j<256*5; j++) { // 5 cycles of all colors on wheel
    for(i=0; i< strip.numPixels(); i++) {
      strip.setPixelColor(i, Wheel(((i * 256 / strip.numPixels()) + j) & 255));
    }
    strip.show();
    delay(wait);
  }
}


// Input a value 0 to 255 to get a color value.
// The colours are a transition r - g - b - back to r.
uint32_t Wheel(byte WheelPos) {
  WheelPos = 255 - WheelPos;
  if(WheelPos < 85) {
    return strip.Color(255 - WheelPos * 3, 0, WheelPos * 3);
  }
  if(WheelPos < 170) {
    WheelPos -= 85;
    return strip.Color(0, WheelPos * 3, 255 - WheelPos * 3);
  }
  WheelPos -= 170;
  return strip.Color(WheelPos * 3, 255 - WheelPos * 3, 0);
}

Process

I had to remill the board several times while making the dimensions larger so that the ground plane would not get disconnected.

After placing surface mount components and reflow:

I left pads to solder wires to that connect to my Arduino Uno to program the ATTiny85. While programming, something went wrong and I could no longer get a device signature from my ATtiny85. I ended up replacing it with another one which worked.

Mistakes in Board Design

After receiving the battery holders, I found out that they are different from the part I used in the board design. The ground pin is on the side and not in the center (as it is in the board design file). I soldered a wire to connect the ground plane in the center to the side plane which was not connected to anything. I then soldered the battery holder on top of that. While programming, I realized I also made a mistake in the board design and forgot to add an external pull-up resistor to VCC on the reset pin of the ATTiny85. I also did not add a resistor before my first neopixel which is recommended by Adafruit.

Documentation Images