Programmable Earrings

Introduction

I make beaded jewelery using tradition materials (mainly glass beads from my favourite bead shop, YumYum Beads). One day I was soldering up an electronics project and I thought it would be great to make earrings out of electronic components as they look neat. Then I wondered if I could actually make earrings that did something so I made these.

Programmable earrings

The earrings are really an exercise in minaturisation. The original circuit was prototyped on bread-board using 0.1" components. But it was obvious that I couldn't use these for the finished article. Also I had to find a way of powering the circuit. The circuit board, components and power source all had to be light enough to dangle from an ear lobe.

Schematic

Programmable Earrings Circuit Diagram

The circuit diagram is actually very simple. Since I knew I only needed 3 outputs and 1 analog input I chose the 8 pin ATTiny25/45 parts (They differ only in RAM, one has 2KB and the other 4KB). The RGB LED is a common anode part supplied by Oomlout. After some experimentation I opted on a 12mm 3V coin cell. This seemed to have enough mA/hr to drive the earrings for a reasonable length of time whilst having the weight and form factor required. In addition there are discretes for the LED, LDR and decoupling.

PCB

Due to minaturisation where possible surface mount components were used and the board is double sided. Since the LED and LDR are through hole parts they had to clear the battery. The battery retainer is soldered to the back. The PCB provides the negative connection and the retainer the positive one. I chose the size of the surface mount resistors and capacitor based upon what I thought I could reasonably hand solder. The IC is also hand soldered with solder braid used to remove any excess.

Programmable Earrings PCB

There are two faults with this board: The screen print for the battery is on the top of the board and so crosses solder pads and has to be scraped off in places; and the holes for the LED are not big enough and I have to drill them out removing the through hole plating and requiring soldering top and bottom. I used 0.8" thickness board for weight which can be trimmed with scissors.