The construction is simple providing you have the secret ingredient which is a length of RGB lighting strip based on the HL1606 LED controller from Wuxi Asic's Corp in China. I got mine while on a business trip in Shanghai. These light strips are becoming popular for signage and architectural lighting around the world. I have attached a picture of the 5 Meter strand I bought along with it's controller box. While they aren't common in this country (yet), there are several suppliers in the orient who will ship you some of this magic stuff. Check out these suppliers. Supplier 1 , supplier 2. There will be many more soon, no doubt ! (Note: watch this space.. I think I may be buying some of these stripes from China soon. I'd be happy to get some for folks if there's interest)
These light strips consist of a flexible copper tape with very (!) bright surface mount RGB LED's spaced at every inch. Each pair of LED's is controlled by an HL 1606. The strips are sold in many lengths each composed of shorter lengths which contain 20 LED's with 10 driver chips. My headband is made of one of those 20 LED segments.
The real trick to making this work was reverse engineering the HL 1606. This chip is a mystery.. with no English language documentation, and only very marginal documentation in Chinese.Using a scope, a demo driver I purchased, and rough translation of the documentation I was able to reverse engineer the signaling required to drive the strips.
The input signaling uses a Serial Peripheral Interface (SPI ) bus which uses one data pin (D_I) .. and a clock pin (C_I) to shift in the control bits to load the color info to the strip. A Latch signal (L_I) is used to latch the data for one HL 1606 and pass it's old data to the chip on it's right. There is also a pulse width modulation (PWM) control pin (S_I) which controls color brightness and fades. Note this project does not use these fade features due to code size restrictions.. but they are very cool to explore.
Once I figured it out, it was pretty straightforward to program a micro controller to drive the strips. I used a PICAXE 08-M . I chose the PICAXE because a) I had them laying around :-) and b) they require very few external components to use.
The PICAXE 08M is a Microchip PIC12F683 which comes preloaded with a simple tokenized basic interpreter The PICAXE family as a nice, easy to use integrated development environment which is available free of charge for download here.
All that was left was to write the code, download it to the PICAXE, and solder it together. Happy Building !!!
Step 1: Cut the light strip to length
To cut your own headband, find one of the soldered connections attaching the fist set of 20 LEDS to the next section. Carefully cut at the soldered connection with sharp scisors. Use a fine tip, low heat soldering iron to clean off and re-tin the solder connections to the strip segment you just cut.