The Blinkring, an interesting piece of electronic jewelry, is also an interesting display of PCB construction and an inventive use of paperclips.
Over in the Dangerous Prototypes forums, Bertho Stoltiens has been sharing an interesting project that puts a blinky party on your earlobes. The Blinkring is an earring roughly 31mm in diameter with 12 LEDs spread around its face.
The concept was to use a standard Cr2032 coin cell and make a printed circuit board (PCB) that could fit around it, effectively making the PCB the battery holder. The little bit of space left over around the cell would house all the electronics necessary to run the LEDs. Stoltiens had some challenges ahead of him on this project. He would need not only a visually pleasing way of holding the battery, but also a switch that someone could manipulate easily while wearing the earrings.
The battery-holding clip was made from a paperclip. Stoltiens said in the forums that the small curves you can see on the clip supply a much-needed spring effect that allows it to sit flush on the battery after installation. On the opposite side of the PCB is the user interface switch, which is also constructed from a paperclip and has a small loop to give it some spring action. The paperclip looks surprisingly elegant in both cases. Stoltiens said on his personal blog (where you can download the schematic and firmware) that his next version will include an off-the-shelf switch; the process of shaping the switch was very labor intensive.
In addition to the physical challenges of PCB construction, he ran into issues with programming the chip. He's using a PIC12LF1552, which is not programmable by the PICKit2 programmer he was using. A workaround using the PICKit2 Device Data File Editor was necessary to move forward. On top of that, there was a physical issue. The PIC12LF1552 doesn't really have standard ISP headers for programming. Stoltiens came up with a fairly elegant solution. He added five contact points on the back of the PCB and made a custom programming dock to hold the earring when updates were needed. You'll note that the pads on the PCB are spaced at 100mil intervals, so he could use pins through verto-board as his dock.
The LEDs are arranged in six spots. Each spot has a red and a green LED. He was hoping to achieve uniform brightness through hardware, but he ultimately had to tweak the software to get the LEDs looking right. He simply has the green LEDs remain lit for roughly twice as long as the red ones during any activity.
There are several modes of activity; all can be accessed by hitting a single button. If the button is held, the unit turns off. It will wake the next time the button is pressed. Stoltiens said on his blog that the unit can run for 100-200 hours and will last for more than a year when asleep.