Friday, November 7, 2008
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.
Wednesday, November 5, 2008
After a certain someone nearly threw our 'alarm clock' (mobile phone) out the window the last time Britney Spears woke us up (Blackout has GREAT wake up songs) it was decided that perhaps we should have our own alarm clock. Since a friend inherited 15,000 of said VFD tubes (Russian Made), and had some odds and ends from an electronics factory that were no longer being used; we decided it would be interesting to solve our 'alarm clock problem' with these.
Components are new but have been rejected from the assembly line in the electronics factory, normally due to bent pins and other mild deficiencies. We saved these throw-aways and used them for the clock. The circuit boards used were custom designed and manufactured using a rapid prototyping process (CNC Machining). Three plates (boards) were specifically designed; one for holding the displays and interface button, one for the clock electronics and one for the speaker, and to act as a base for the entire clock.
The processor uses a 16mhz crystal to generate the time signal. The 16mhz signal is first divided by eight and then by two thousand to generate a one second pulse. The program counts the seconds to form the minutes and hours. These are then displayed on the tube.
The interface was designed to give the user a fluid experience when setting time, alarm, and snooze features. The time is set by holding down button one, which stops the dot flashing. Once the dot stops flashing, the time can be programmed. Hours are programmed with the left button (1) and minutes with the right button (2). To set the alarm, the same process occurs but initiated by the right button (2). When the alarm goes off in the morning, there is a snooze feature, which can be 'snoozed' by pressing left (1). To turn off the alarm, hold down the right (2) and press left (1). The best feature? An innovative snooze twist, the clock flashes between time display and the word "Sn" when it is snoozing! Finally you know if your clock is on snooze or if its turned off... We are working on a new feature which may display how many minutes are left between the last snooze and the upcoming buzz. Speaking off, the buzz is hopefully going to be replaced by our great Arduino synth which is capable of outputting some truly fantastic music. We are also considering a dimmer function, the VFD tubes are capable of having their brightness adjusted, and the circuits are prepared for a light sensor, we just have to work it into the interface!
The electronics for driving the VFD tubes is a bit tricky, it needs a slightly higher voltage than the normal 5V signal used for typical LED clocks. The VFD uses 35V as well as a 1.2V filament voltage. Apart from driving the clock and user interface, the processor also has to control the generation of these voltages. Each VFD tube works like a regular 7 segment display, and are actually driven exactly the same way. The processor switches rapidly between the four tubes, so that only one tube is lit at a time (multiplexing). As such you can see eleven little legs, (pins) eight of them control the anodes (segments) within the tube. Two of them have filaments connected between them, and one has a grid which enables or disables the entire tube. All the anodes for the four tubes are connected in parallel and the processor uses the screen to switch rapidly between the tubes. This makes it possible to write individual digits on each tube using only eight common pins.