CogHack #26: Tangible output: Theremin Birdfeeder
To fulfil the tangible output brief of this hack day I started with the material. Every year I trim the willow hedge in my garden and think I should really do something with the offcuts. After all people have been using the unique properties of this material to produce interesting and useful things for thousands of years, so I could probably manage something.
Making my own aspirin seemed unwise so I looked around for project ideas that seemed achievable for a novice willow weaver and I came across these conical birdfeeders.
Nice enough but not quite hackday worthy yet. How to elevate this to something a little more technical? In the office we have a theremin kit from the open theremin project. A theremin, for those unfamiliar, is a musical instrument played without touching it through electrical conductivity of the body. Could I use this to alert me to birds visiting my feeder, and would they play beautiful music?
The weaving itself was relatively straightforward. A little tricky in the first few bends with 5 strands to keep track of but once you get going the pattern becomes simple to follow. I had soaked the willow in advance to make it more pliable but there were still some sections that cracked far more easily than others. Whether this was down to insufficient or irregular soaking or just the natural variation in the wood I couldn’t say.
The theremin itself consists of two aerials: a straight vertical aerial which controls pitch and a horizontal loop which influences volume. Ideally I was hoping for the output to be silent until the feeder was approached and for the volume and pitch to change as the bird moved through 3d space. The standard setup for a theremin is that volume decreases with proximity, which is the opposite of what I wanted. For now I went with embedding the pitch aerial in the feeder and mounting the volume loop below so that it was generating a continuous tone. By messing around with the calibration and controls I was able to get the base tone at a very low frequency that was less audible and rapidly ramped up as you approached.
The final element here was to find a test bird. In my mind’s eye I had pictured a charm of goldfinches or a squadron of long tailed tits gently interacting with the device as they darted in and out. Sadly the Cogapp offices are on the 8th floor and the only avian visitors we get are pigeons, seagulls, and (very excitingly) the occasional passing peregrine falcon. If you have ever met a Brighton herring gull you will know that they are mighty and terrifying beasts. My creation would not last long in their inquisitive beaks.
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I was going to need a proxy bird. I didn’t have time to learn the science behind body conductivity and research and reproduce the electromagnetic properties of a sparrow so I went for a piece of fruit and some trial and error. A kiwi had the duel advantages of being the right size and at least having the same name as a bird, but tying one to a piece of string and dangling it near the aerial produced no effect at all. Rubbing it on my jumper to build up charge? Still nothing. Wrapping it in tin foil for a more conductive surface? Nothing. Wrapping copper wire around the kiwi to produce a coil? Very faintly, there was a change in tone coming through the speakers. Moving the coil so that it was wrapped around and running up the string made this effect much stronger. This was even more so if I was touching the bare end of the wire as a sort of human-fruit cyborg. Worrying that this was just because I was grounded and therefore not sufficiently birdlike I stood on the desk. A little decoration was required and, kiwi’s being flightless birds, the tin foil came in handy for it’s robot wings.
The open theremin kit is built on an Arduino microcontroller with all the audio being produced digitally on the chip after sampling the input from the aerials. As the software is open source and the Arduino re-programmable I could in theory adjust the behaviour to better match my use case by inverting the function of the volume aerial, or setting a threshold on the tone signal for when it would start emitting output. After some messing about getting the Arduino connected and logging data it was getting close to the end of the day and I decided not to risk re-programming just before demo time.
Being a primarily backend developer much of my work is not only screen based but not even visible to the end user and so getting to build an actual physical thing is a bit of a treat. Did I prove that the idea was viable? Not entirely. Did I learn anything? That theremins are very sensitive and fiddly pieces of equipment.
I did get a new birdfeeder out of it and I have set it up at home in the hope of attracting some birds before connecting the electronics to see if there is a response. So far they have not shown much interest. One problem is that positioning is limited by needing to connect the power and audio out cables. The theremin itself is low power and could happily run off a battery pack while a small battery powered F.M or bluetooth
transmitter would allow free placement with the audio playing far away without disturbing the visitors. Finally the electronics would need weatherproofing, which would be easy enough with an old takeaway plastic box.
Steve is a Developer at Cogapp, a digital agency specialising in the cultural sector. Please get in touch if you’d like to hear more about our work.
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