I often like to keep a side project in the back of my mind. It helps to occasionally give my brain a break while still keeping it active. One semester I decided I wanted to make a RGB LED Necklace for my girlfriend. I began making some back-of-the-envelope sketches in the margins of my school notes.

Eventually I picked out an I.C., the lp5521, that seemed to do everything I wanted (great current control, fully programmable 3 output sequences). I went ahead and designed a simple PCB and sent it out for manufacturing by Seed Studio’s Fusion PCB service.

While I was waiting for the PCBs to arrive I wanted to start experimenting with the controller chip. Unfortunately the footprint was really small, so I glued it upside down and used strands from a threaded wire to break out the pins.

Once I finally began interfacing with it, I found out I had overlooked something crucial in the datasheet. The program memory was not permanent, any light programs created were immediately lost when powered off! This was disappointing since I had wanted the microcontroller to be standalone without a master chip that had to reprogram it every time power is restored. Since I had already ordered the PCBs and the semester was coming to a close, I decided to hack together something anyways. The result faded the the LEDs in and out for as long as the battery lasted.

I’ll definitely be revisiting this idea to make a much better version. I would like the next form factor to be a cube bead instead of a pendant. It would also be a neat feature to make it wirelessly controlled. This would open up options of changing colors based upon status updates from a smart phone or even using a wireless heart rate sensor to make the necklace pulse in sync with the wearer’s pulse.