When pieces of junk get together with a purpose...

Beautiful things can happen.

(Dangerous things can happen too)



These are some sketches of electronic projects and `at home' science experiments that I have enjoyed making over the years.

Many are built from `junk'. In the twentieth century we have produced a huge amount of unwanted electronic equipment, from household appliances to specialised research equipment thrown out at laboratory dumpsters. For most of my life I have collected, taken apart, stripped or reused such junk, sometimes for pragmatic reasons. Sometimes to procrastinate. Sometimes I just can't bear to see a beautifully designed piece of gear go to waste. I am not alone in this craving. It seems commercial interests are driving us away from repair and reuse and towards disposibility. I believe it is important to retain and propagate knowledge about repairing our increasingly electronic surroundings. Even proper recycling/reuse of computer equipment can make a huge difference in your institution/community. One exemplary organisation which puts this to good use is the American Medical Resources Foundation.

Under construction: photos and links may follow, time pending. Email me with questions or ideas.


Microwave doppler radar.

Converts motion into audio using 3cm wavelength 10mW CW source and mixer. Reflections off passing people and vehicles at a couple of hundred yards can be `heard'.

Here is a description from a recent MIT science education day:

Materials: 10 Ghz (X-band) `burglar detector' doppler module, available from Radio Spares (UK) (Equivalent US model unknown, but I am sure educational science supplies stock something similar). Power supply for module, audio amplifier, speaker system. Flat pieces of aluminium foil, and balls of aluminium foil on strings.

Module is basically a radar: it emits low-power (10mW) microwave beam, and mixes any received waves (reflected off nearby objects) with a little of the transmitted ones. The interference between the two generates beats when the reflection is off a source moving towards or away from the unit. This beat signal is then turned into sound by amplification and a loudspeaker. Roughly you get one cycle of audio sound produced every 1.5 cm of movement of a reflecting object. Anything which is conductive reflects the microwaves, including people walking around the room. Aluminium foil is a good reflector (this was used in 2nd world war to confuse German radars), and you can whizz the foil balls around to hear the sounds produced. The pitch of the sound is proportional to the speed of motion. Motion of a few meters per second gives nice singing tones of a couple of hundred Hz.

3D Stereo Shadows.

Red/green 50W halogen point sources of light and red/green filter spectacles gives scary 3D shadows on walls and hanging bedsheets... this is amazingly vivid when set up correctly! It has proven a great diversion at dance parties. The halogens need to be an adjustable distance apart, to vary the strength of the perspective effect. It would make a great exhibit for Burning Man. As far as I know this simple idea is my own invention - I have never seen it anywhere else.

Pulsed nitrogen gas laser.

My design basically followed that from the old Amateur Scientist columns of Scientific American magazine from the 1970s. Except I extended the discharge volume length to about 1 meter, and used a 1 meter by 0.8 meter sheet of 1/16 in double-sided copper-clad circuit board charged to about 20kV. It gave nice collimated pulses of UV, but had a leaky vacuum system.

Ultrasound beam in water.

Pull apart a $10 yard-sale ultrasonic humidifier and beam a few watts of sound around underwater (caution: do not burn yourself internally; this can be very painful and take months to heal, I have been told by ultrasound researchers). Radiation pressure (a few grams force, so you can feel it with a spoon!) due to reflection off the water's upper surface is very easily visible, especially using a reflected light source. Wavelength is about 1 mm, sound power output about 5 watts (most easily measured again by radiation pressure). The power is such that bubbles (from dissolved gas) will collect at standing wave antinodes, and streaming of the water is visible. Plastic spoons are easily melted. The insides of your fingers too, I imagine.

Optically-stabilized magnetic levitation.

Levitation of ferromagnetic objects via light-beam-controlled feedback mechanism and 4-amp home-wound solenoid switched by ubiquitous 2N3055 transistor.

Playing around with gizzards of microwave ovens.

Not recommended unless you have a lot of experience with high voltage gear and safety procedures! Danger of injury, blindness (and sterility) due to heating of body parts! Generally very dangerous, just don't try it unless you have RF and high-voltage experience.

Lots of fun for standing wave demos, lighting fluorescent lights at a distance. Ultimate aim is to drive with pulses and set up solid-state wideband receiver + amplifier to give primitive radar. Potentially not very friendly to the local 2.4GHz-band users.

Tesla coils and RF generators.

Not very friendly for the local AM radio listeners, but lots of fun with 6 inch sparks (which are generally safe due to skin effect). RF generators made from self-oscillation of old audio PA tubes, gives fat little blue RF arcs when stepped up via a few turns air transformer.

Audio electronics.

Refurbishment of Hammond organ, design of effects pedals, experimental sounds.