Friday, November 7, 2008
Biometric Jewelry Continued...
The circuit board has been routed using a CNC machine to create the intricate details, twists and turns that make this piece unique. In case you're not familiar with how circuit boards are made, here it is. A very strict and detailed process was followed to create the project. First, a design was created using an image of a celtic triangle. This was then mapped into a vector art program, and traced over. The circuit diagram was laid overtop, and all cut lines, drill points and cut outs were defined. To create the circuit board, first transparencies were printed, matched, and is contact copied in a UV light box which transfers the image from the transparency to the circuit board. The circuit board, which is covered by photo resistive material is then covered with a chemical, which removes all the photo resistive material except that which has the pattern from the transparencies imprinted on it. The circuit board is then put in an etching machine, removing all the copper not covered by the photo resistive material. This reveals the copper tracks.
The CNC machine is used to drill holes where they are needed (for components, etc). The outlines of the pattern are then routed into the circuit board and the outline of the shape is established. The CNC machine then details the shape, drilling and etching to reveal the final celtic knot triangle.
Once out of the CNC the components were soldered on to it and all copper traces are covered with solder. Components that should not be painted, such as the LEDs, are masked off with masking tape and then is sprayed with paint and put in an oven to cure. The tape is removed, and a glowing heart rate monitor is revealed.
The LEDs are programmed in a special way since the micro controller (AVR Tiny45) is so small, with few pins, all the LEDs are connected in such a way that only a single one can be lit at a time. In order to give the impression of each LED having individual brightness to create the waving motion, very fast multiplexing was implemented. (i.e. switching between LEDs very rapidly, varying the time each LED is turned on).
The necklace itself has a heart rate receiver, receiving pulses from the heart rate monitor.
The heart rate portion is borrowed from a previous project, so every time a heart beat occurs, the LEDs light up in a pattern wherein each LED receives an individual brightness to simulate ambers glowing in synch with the heart rate, and fading out over time.
The processor, five LEDs and a capacitor were all that were used on the necklace. In a moment of minty inspiration, we used a Listerine breath strips container to house a lithium polymer battery, however we are contemplating using lithium coin cells instead for easier replacement rather than charging.