RASPBERRY PI

ProjectsSHOWCASEPUTTING JOYTONE TOGETHER>STEP-01Custom circuit boardsAt the heart of the Joytone are nine printedcircuit boards (PCBs). These make the Joytonemore reliable and easier to fix than earliermodels. Dave signed up for TechShop in SanFrancisco to learn how to design PCBs.>STEP-03Arranging the boardsNine PCBs, each containing eight joysticks, arearranged into a square in this offset pattern.With two signals per joystick, there are 16analogue signals generated by each row.>STEP-05Raspberry PiThe Arduino looks up the MIDI note itrepresents and sends that information upto the Raspberry Pi, which then uses it tocreate the audio sound.>STEP-02Fitting the joysticksThe clear joysticks and lights are fitted intothe PCBs. Rather than use individual lights, theJoytone employs a strand of 25 Digital RGBLED Pixels (adafruit.com). These are easier tofit and more reliable than individual LEDs.>STEP-04Multiplexer and ArduinoMultiplexers are used to connect the PCBs tothe Arduino Mega. They enable the Arduino toexamine the position and movement of all 72joysticks at once.>STEP-06Played with sticksA sheet of acrylic is laser-cut into a honeycombshape to hold the joysticks. A box holds all theequipment, and the device is ready to play. Asingle finger is used to play each stick and youcan play up to six notes at once.The softwareThe Joytone depends on PureData(puredata.info): “You can connectblocks with lines to direct theflow of data through a series ofmathematical operations, toproduce all kinds of strange anddelightful behaviour.”Dave built a PureData patch forthe Joytone. “[It] receives MIDImessages, then unpacks themand passes the values inside intoa group of blocks that produces asynthesized note,” he explains.“The pitch is controlled by thejoystick the user chose to push,”says Dave. “One axis of the joystickcontrols the kind of waveformproduced. It fades from a brighttrumpet-like sawtooth wave to adarker triangle wave that soundslike a bell.” The other axis of motioncontrols how flat or wide the notesounds by making a small tuningdifference between the pair ofoscillators that produces the note.“All of that expressive potentialis represented in the groupof blocks in PureData,” Davetells us. “There are six of thosegroups in the patch, meaningthe Joytone can play up to sixnotes simultaneously.”Playing the JoytoneWhile the idea behind the Joytoneis complex, playing it is surprisinglyeasy. “My friend who helped mebuild the first one in school is avery talented musician,” affirmsDave,“and the first time we got itworking, he played with a coupleof the joysticks, then pausedand thought for a second, thenimmediately played a Bach fuguehe was familiar with. It was anawesome moment of success after astring of very long nights.”Playing the Joytone is remarkablystraightforward. The joysticks areplayed with a single finger. “It’seasy to hold your hands as if youwere typing on a keyboard,” advisesDave, “and play many notes atonce. The joysticks are pretty closetogether, so the player has accessto a large musical range with prettylimited hand motion.”36 August 2015raspberrypi.org/magpi