Introduction: Anachronistic Audio: Radiation Windchimes
The final piece of my Autodesk Artist-in-Residency and the Anachronistic Audio project is called Radiation Windchimes. To complement the rest of this body of work I wanted an instrument of sorts, something that produced audio to be altered and amplified by the other pieces. Around that time I had been thinking of using radiation as a random audio source for a separate project, so I changed that idea around a little bit and decided to instead build the Radiation Windchimes.
Step 1: Why Radiation?
Of all the art pieces, contraptions, circuits, and projects I'd done in the recent past, this is really the only one that has an intentional point to be made at its core. After the Fukushima disaster (which I'm not in the least trying to trivialize, mind you) there was a huge rash of fear-mongering, speculation, and misinformation by various non-credible news sources which, as usually happens in the internet age, got re-quoted, up-voted, re-posted, etc all over social media. Some of my friends who I thought were relatively intelligent started posting about "Fukushima radiation reaching California" and other sensationalized articles with exaggerated facts and false maps. Yes, it's true- atmospheric radiation shortly after the event was detectable here: in the most miniscule amounts imaginable by the most sensitive detectors on the planet. That was expected.
Ok, so Instructables nor my artist residency are my personal soapbox, and I don't intend to use them as such. The purpose of this artwork is to make one step back a bit and think, in light of all the hysteria, that radiation is around us all the time. The Alpha, Beta, and Gamma background radiation from space, medical equipment, building materials, our food and water, and countless other sources are moving through the air constantly, like a radioactive breeze. Hence the wind chimes as an indicator and reminder that it is always there.
Radioactivity... is in the air for you and me. -Kraftwerk
Step 2: Electronics Design and Prototyping
To start investigating how to build this piece, I ordered the MightyOhm Geiger Counter kit from the Maker Shed. This basically is a small battery-powered DC boost power supply, a detector circuit and microcontroller, and a piezo speaker and LED. Using their open-source documentation as I guide, I did a board layout for a much smaller circuit board utilizing SMD components that would be embeddable in the final piece.
My boards had a three pin connector to bring power and ground to the board, and the signal off of the board to the control electronics. I decided to stick with the SBM-20 Geiger–Müller tube for aesthetics and because it was easy to order a large surplus lot of them from Ukraine. The boards required quite a bit of rework to get them to a functional and stable working state. Many of the SMD parts weren't rated appropriately for the higher voltages involved in this circuit, and the HV rated versions weren't available in the package footprints that I used on the PCB so they had to be airwired.
Just as a side note, there are two fundamentally different types of GM tubes. There's the metal type like the SBM-20 which can detect beta and gamma particles, and the more expensive mica glass window type which is also sensitive to alpha emissions. This is a handy site listing some of the available tubes and comparing their sensitivity:
Step 3: Wind Chime Sampling
I have a set of wind chimes in my backyard that I bought at the mall when I was 14 or 15 years old. They've got a lovely tuning and nice deep tone that made them worth holding on to for over 20 years.
Using my handy (and pretty destroyed) ZOOM H4 field recorder, I struck each chime with a wooden block in sequence and let the tone ring out. Then I took the recording into Sound Forge, split it into separate samples, adjusted them for consistent volume across all 8 sounds, and cropped out any dead space. On a few of them, I used a mild compression to reduce the original attack spike where the wood hit the chime to avoid popping sounds later on in the process.
Step 4: Software and Pd Patch
Anticipating that I would eventually be running this on an embedded device such as a BeagleBone or Raspberry Pi, it seemed appropriate to write the sampler code in puredata.
Talking to some other AiRs, I discovered there is an awesome software distribution called Satellite CCRMA that is available for both of these platforms. Developed at of the Center for Computer Research in Music and Acoustics group at Stanford, this software image basically boots the Pi into a system ready to do interactive audio installations with Pd, various audio drivers, easy integration with Arduino as an input device, and good documentation. It was simple enough to develop the Pd patch on my Mac Mini and FTP it over to the Raspberry Pi for testing the actual embedded system.
Now I'm certainly not a Pd expert, but by starting with some basic samplers and the pduino patch I cobbled together the patch in the screenshot above which looks for state changes on the input pins of the Arduino. These pins are connected to the Geiger counter boards and toggle upon a particle detection. The Arduino debounces and mildly attenuates the triggers for aesthetic purposes before passing the signals up to the Pd patch. The patch then triggers the associated wind chime sample.
Step 5: Making the Wooden Object
I thought it would be most poignant to construct the array of Geiger tubes on a base of the universal radiation symbol. To stay within the aesthetic realm of the other projects in the series I wanted to use nicely finished wood so I decided to form the symbol using a laser-etched inlay procedure I had been experimenting with earlier in the shop.
Firstly, I cut the front and back pieces out of plywood on the ShopBot. In the picture you can see the back piece on the left with the wells for holding the electronics. The front at this point only had the holes which would carry the high voltage through to the Geiger tubes.
Next I used the laser etcher to raster etch a depression which would hold the contrast wooden inlay. As seen in the third picture, this was almost a two hour etching job! I've been informed that this would have been much quicker using the router and a chisel to sharpen the corners, but the point was to try a new technique.
Then I cut the inlay pieces out of walnut veneer and glued them into the laser etched wells and sanded it all flat when dry.
Step 6: High Voltage Standoffs
In order to mount the Geiger tubes on the face of the wooden piece they would need to be isolated by some fairly non-conductive material. I chose to use the ceramic insulators usually found on electric fences with a homemade thumbscrew assembly to hold the tube in place.
In the above picture, you can see the stackup which would be installed on the front wooden piece. Starting with a forged eye-bolt, I tapped a hole straight into the top for a thumbscrew to hold the Geiger tube. The ceramic insulator sits on top of the wood, and a delrin bushing sleeve keeps the bolt electrically isolated from the wood. A combination of a delrin washer on the bottom and metal washers on both sides squeeze the whole assembly tight against the wood when the nut on the bottom is tightened. Voila!
Step 7: Installing the Electronics
After the standoffs were all mounted, it was time to glue the two wooden pieces together and to install the electronics.
Whoops! Guess I'll need a cable chase to get the three-conductor power/data cable to each of the Geiger PCBs back to the central cavity. Hammer and chisel time.
The bottom and top were glued together with Titebond and clamped overnight.
I quickly cut some rectangles out of phenolic and used VHB to attach them to the piece, followed by mounting the PCBs. At this point I also ran the wires through the chases in the wood and hot-glued them in place. The orange wires you see above are rubber coated HV-insulated cable which will carry the ~300VDC from the board to the eyebolts by having ring lugs attached and being tightened under the washers.
Step 8: Testing the Geiger Tube Array
Next I brought the whole shebang up to the electronics lab to check the circuitry and the installation. The drive PCBs have trimpots to adjust the voltage output, so I adjusted all of the board to roughly 300VDC. I also put a scope probe on each of the PCB outputs and verified that they were all detecting particles (you can see the negative pulse on the scope trace indicating a detection event).
After troubleshooting and finding a bad SBM-20 tube, all six of the tubes/PCBs were working perfectly and it was time to install the controller.
Step 9: Raspberry Pi Is Taller Than Expected...
Ugh. Even with all right angle adapters for the power and audio output, the Raspberry Pi was still a bit too tall for the cavity I had prepared. And to make things worse, our ShopBot was offline and moved to a different building.
To remedy this, I took the CAD files back to the Metabeam and cut an additional 1/2" backing piece and glued it on. For some reason, this was an incredibly difficult and sooty cut, way moreso than most work I've done on the metabeam. Must have been something in the plywood formulation. Regardless, it got the extra clearance that I needed to finish installing the electronics.
Step 10: Connecting the Pi and Arduino Micro
To make all of the controller connections, I first soldered the trigger outputs from each of the Geiger PCBs to an Arduino Micro which would be running a slightly modified Firmata firmware. The Micro would then be connected to the Pi over USB to provide input signals to the Pd patch.
I flashed the Satellite CCRMA distribution onto the SD card per their instructions, logged in over ethernet and installed my Pd patch, and set the Pi to auto-load the patch on startup. When the Pi rebooted, I had the lovely sound of windchimes in my headphones!
Step 11: Internal Speaker System Installation
It dawned on me at the last minute that having the Windchimes be a totally self-sufficient installation would make it easier for gallery display, and that it wouldn't be too difficult to integrate speakers into the artwork. Since it was effectively a big block of wood, a pair of surface transducers should be able to make it resonate while taking up very little room.
To add this system to the piece, I switched the power supply to 12V and installed a DC/DC buck regulator to provide the 5VDC for the control electronics. Next I wired in a small power amplifier with a 1/8" patch cable input from the Raspberry Pi and stuck two surface transducers on either side of the piece. Luckily for me, they sounded great even at moderately loud volumes.
Step 12: Final Piece, Video Example
After making a display stand, the piece was complete and functioned very well. The windchime sounds are eerie eminating from the front panel of the piece and are a nice indication of omnipresence of radiation. These detectors individually will usually pick up around 20-30 detections per minute just from background radiation, so I adjusted the code to attenuate this a small amount so that it didn't constantly chime.
In trying to adjust the code to add a retrigger delay on the sound samples, I inadvertently discovered a pretty cool "feature": super fast retriggering of the sound samples actually causes a sound that is similar to an actual clicking Geiger counter! Since I thought it was cool and people usually don't roam around galleries with their own Cesium-137 samples, I went ahead and left the code alone.
Overall, the piece came out exactly as planned. I also must give huge props to the CCRMA group at Stanford for their work on Satellite and the amazing projects they do to push the boundaries and drive interactive electronic music forward.