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.

Physical Hardware:

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

VFD (Vacuum Florescent Display) Clock

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.

Wednesday, September 17, 2008

Active Energy Harvester

We are investigating different survival techneques for micropower devices. Rather than cleverly managing whatever energy is available to an inanimate device it is interesting to see what advantage devices that actively hunt for energy may have.

This project is a solar powered robot that uses a tiny RC-servo to slowly scan the surroundings for solar power. Like some flowers it follows the movement of the sun during the day.

All energy needed to move the solar panels and run the robots microcontroller is stored in an tiny Lithium battery during time with excess solar energy. During nighttime the mechanical function is shut off and only the robots brain is kept running. During periods of energy starvation the robot goes into deep hibernation saving the battery from being destroyed by deep discharge.


Friday, August 29, 2008

Message in a balloon

Continued from "Message in a Balloon" at GeekPhysical

As part of the ongoing micropower device research we wanted to explore environments where no external power sources were available. The aim is to create a tiny model satellite that will survive for as long as possible attached to a small helium balloon. This project is an attempt to create an small and disposable radio transmitter that can be carried by a party balloon and eventually be powered by a tiny solar panel.

In its current version the transmitter morse-codes a radio amateur call sign and identifies itself. For the final project we call upon the radio amateur society to pick up signals from the satellite, log its time and position and report back to a dedicated website. The test transmitter was flown on tethered balloons for several hours to test the range and durability. The message was picked up by several pre-warned radio amateurs at various distances from the test-site.

Our future plans for this project include the use of solar panels, arranged in a triangle formation, which would always be pointing to a source of sunlight, and could thus power the device without the need for external power.

Listen to the message recorded by an radio amateur.

Wednesday, August 27, 2008

Finding Stuff in the Sky

Continued from "Finding Stuff in the Sky" on GeekPhysical

As an artist and experimenter you may come across the problem of finding something or someone in your surroundings and needing to pointing some kind of sensor at them.

First, one needs to acquire an initial position, and thereafter retain a lock on the object need to be performed. One method of achieving the initial position is to first scan the whole space where the object may be located using the sensor(s) and then choosing the position with most/best sensor signal. Once the initial position is acquired a smaller part of the surroundings may be continuously scanned to retain knowledge of the position even if the object is moved.

Antenna tracker

We are doing long distance flights with RC video planes. During these flights a high-gain receiving antenna must be pointed directly at the aircraft. The antenna is mounted on a post with servos enabling it to pan and tilt in such a way that the whole sky can be pointed at.

A microcontroller system is then connected to the servos and a receiver measures the strength of the signal received by the antenna. Initially, the microcontroller has no knowledge of the aircraft position and needs to scan the sky for a suitable signal. Since the antenna is long and flexible it is desirable to use harmonic rather than abrupt movement thus the search pattern chosen is a spiral motion starting from an arbitrary point in the sky and moving outwards.

Once a position with sufficient signal is encountered along this spiral path this is chosen as the lock position. Hereafter the antenna is moved around the initial point in a smaller circle and the point with maximum signal strength is recorded. After each circulation the initial point is moved towards the maximum point. This results in the antenna continuously improving its aim towards the transmitter.

To prototype this system an LED was used as the transmitter and a photo transistor as the antenna/receiver. The LED was modulated to avoid interference from surrounding light sources.

Self sustaining micropower devices - aka, a sexy new doorsign

Continued from GeekPhysical - Sustaining Micropower Devices

Many (interactive) electronic devices spend most of their time doing nothing or very little. The ratio between usage and inactivity often results in an extremely low average power consumption. This opens the opportunity for powering such devices from very weak but ever-present power sources.

To explore the possibilities for having an active electronic microcontroller-based device without the need for any expendable power source we have developed an LCD door sign that will run day and night powered by a tiny pocket calculator solar cell.

Miniature solar cells like those found in pocket calculators will, in favorable conditions deliver a mere 100µA @ 3-4V and since most microcontrollers require at least a couple of milliamps to run some sort of power management is required.

The microcontroller used in the project(1) has the ability to shut itself down reducing power consumption dramatically. An internal timer can be programmed to 'wake up' the controller at regular intervals to do useful work and then go back to sleep. Using a capacitor or rechargeable battery to store the energy collected between small burst of microcontroller activity allows the average current draw to be reduced to a few µA. In effect the solar panel produces an excess amount of energy over time.

The controller used(1) also has the ability to measure the voltage across the battery/capacitor thus giving a measure of the available amount of energy at any given time. The microcontroller program has the ability to change its level of activity depending on available resources. Our project contains an AVR microcontroller, a small alphanummeric LCD, two pocket calculator solar cells and a tiny 80mAh LiPo rechargeable battery.

The controller scrolls the names of the inhabitants on the LCD thus demonstrating a simple and useful device.

Apart from the display function the microcontroller performs the power management functions required to maintain active over a 24 hour power harvesting period. Further, apart from changing the interval of the activity depending on power reserve the controller has the ability to completely shut down the LCD during times of power starvation.

This project does not imply interactivity but functions could be implemented to keep the device powered during interaction. Other weak energy sources such as electromechanics-, electromagnetic-, static electric or chemical could also be applied.

(1) Most modern microcontrollers have this functionality.