Discovery Synth

The Discovery Synth (DS) as an example of a musical interface which applies techniques of deconstructivism and abstraction to its design. The interface’s buttons and potentiometers seek to replace the mechanical abstractions that separate our bodies from the electronics with the body of the user. The DS is a reaction to the observation that electricity, in its raw form, is of little worth to our society. Lightning arching in rainclouds, or striking the ground, does little to ease the struggle of human existence just as the static electricity that builds on your body as you shuffle along a shag carpet is rarely anything but an annoyance. However, electricity can work miracles when harnessed using the correct tools and the power of electricity, in modern society, comes from the design and implementation of electronic components. As a result, we usually interact with electricity via a physical abstraction or a tool which then electronically modifies the underlying circuitry for us. Let’s take the example of the popcorn button on a microwave, the button physically separates the finger from the electronics that operate the microwave. When pressed, the button internally will connect two points in the circuitry which were unconnected when the button is in its resting state. This connection causes electrons to flow, alerting the microwave’s logic to the certitude that the popcorn button is pressed. The DS project wants to bring the user closer to the electronics they are controlling just as Peter Blasser has sought to do with his own work. The project seeks to remove physical constructs – the popcorn button – which separate the body from the electricity which controls the interface. The Discovery Synth is a Raspberry Pi powered interface used in both installation and experimental music performance. Physically, the device features eight buttons, sixteen potentiometers, stereo output, and microphone input. The Raspberry Pi inside the interface is powered using an onboard battery which can be recharged using a USB cable. The Pi, with the help of a custom cape, is reads the values from the buttons and potentiometers. Pure Data is run on the Pi to make sense of the sensor readings while also serving as the audio and video synthesis engine for the device. The DS Raspberry Pi cape was developed in collaboration with Clay Chaplin for the CalArts AV Ensemble which Chaplin leads. Each of the ensemble members built their own version of the DS and students were free to choose whatever specific components, enclosures, and configurations they preferred for their instrument. The authors iteration features eight custom buttons along with sixteen voltage dividers: eight of which are standard mechanical potentiometers while the remaining eight are custom. The instrument is crafted from reclaimed materials: the buttons and pots are housed in the base of an old aluminum lamp, the main body is crafted out of wood found on the side of the road, and the tuning pegs are salvaged from an old guitar. The Raspberry Pi 2 that acts as the brain for the DS, features twenty-six General Purpose In/Out (GPIO) pins which operate as either inputs or outputs at a logic level of 3.3V. While the GPIO pins are adequate for many circuits, they are limited both by their strictly digital operation and minimal current sourcing capabilities when compared to an Arduino Uno microcontroller. The Discovery Synth Cape gives the Raspberry Pi input capabilities which reflect an Arduino or equivalent microcontroller: bestowing the ability to read analog values from sensors in addition to expanding the available number of usable inputs. This is done with two MCP3008, 8-channel, 10-bit, A/D converters.

Buttons

The DS’s buttons are designed as minimally as possible with no physical mechanism separating the action of pressing from the flow of electrical current within the component. Every part of the design is functional and vitally important for the device to work properly. The process started conceptually by distilling how Normally Open (NO) electro-mechanical push buttons function; they internally contain two conductive paths which are electronically separated when no external force is applied. When a NO pushbutton is pressed, two parts of the circuit are joined through mechanical means allowing current to flow from one lead to the other. The DS’s buttons follow the NO model providing no electrical connection between the two leads while the buttons are in their resting state but allowing current to flow when the buttons are pressed. To refrain from using any unneeded abstractions the buttons consist simply of two conductive bolts, spaced a few millimeters apart. The bottoms of the bolts are soldered to lengths of wire which are connected to the DS cape. One of the bolts is connected to the 3.3v power rail while the other is monitored by a GPIO pin on the Raspberry Pi. By pressing on the bolts with a finger, the interactee fathers an electrical connection – through their skin – between the two bolts.

Potentiometers

The DS interface features a total of sixteen potentiometers in two banks of eight. Each of the two banks contain distinctly different types of potentiometer. The first bank, which this document will refer to as the knob-style potentiometers, are typical store-bought mass produced potentiometers and are mounted in the metal portion of the interface next to the buttons. The second bank, or the slider-style potentiometers, are custom designed just for the DS and do not look like the bank of knob-style potentiometers. The goal when designing the slider-style potentiometers was to remove the physical abstraction wedged between the human and the circuitry in order to create a direct interaction: just like with the buttons discussed above. A potentiometer is mechanical component that functions electronically as a variable resistor. Potentiometers, or pots as they are often called, have three leads they use to connect to the circuity around them. The outside leads are connected to the ends of a resistive material, while the inside lead is connected to the wiper. To adjust its point of contact with the strip the wiper is typically moved using mechanical force to come into contract with the strip at different points producing a varying resistance between the wiper and the outside leads. A common application for potentiometers, and how the DS is using its potentiometers, is to connect the component to a circuit so it functions as a voltage divider. By connecting one of the two outside leads of the potentiometer to the circuit’s power, the other outside lead to ground the center wiper lead will produce a variable voltage depending on its position. The DS slider design functions identically to the conventional potentiometer described above; it has a strip of resistive wire, specifically Kanthal, that comes into contact with conductive copper tape at different locations producing a variable voltage at the wiper node. What makes the slider novel is not how it behaves electronically, but is instead its construction. The DS slider, just like the buttons discussed above, contains no parts that are not completely necessary to it functioning: there is no casing, levers, springs, or anything else. The copper tape exposed on the outside of the DS’s wooded case serves at the sliders wiper and is connected to an A/D converter found on the DS cape while the Kanthal wire suspended above is the resistive strip and is connected to power on one end and ground on the other. One of the primary duties of the DS cape is to provide analog readings from the potentiometers to the Raspberry Pi, which normally is limited to digital readings by the capabilities of its GPIO pins. This is done with two sixteen pin, MCP3008 ICs. The MCP3008, manufactured by Microchip Technology Inc., provides eight channels of 10-bit resolution A/D converters,  can be controlled over SPI, and operates on a voltage range of between 2.7V and 5.5V. With the help of these IC’s, the DS reads a high value from the slider when the user presses its wire down close to the aluminum portion of the interface and a low value when held down on the opposite side. A pecurality of this design becomes apparent when the slider is not being pressed. With no external force to bend the wire down the Kanthal moves to a resting position ½” above the interface, breaking its connection with the copper-tape wiper below. This results in the Pi receiving a reading of “0” for that channel. In this way, the sliders do not hold their last value as a typical potentiometer does and effectively function as “normally-open potentiometers”. Meaning, the sliders only return values when physical force is applied to them, just as a normally-open pushbutton will only return a value when pressed. This quirk is desirable in some circumstances, especially working well for controlling effects, filters, or some sample playback parameters. In compositions with parameters that demand the ability to hold and maintain an intermittent value, they have to be mapped to the standard store bought potentiometers. To partially offset this limitation, the interface is often presented with several copper pipe segments. The pipes are used to maintain an electronic connection between the wiper and Kanthal wire allowing the performer to hold intermittent values on with the components. However, the pipes are not a perfect solution. They work well for holding values, but a awkward when increasing or decreasing a value and overall are clunky to use. The DS project succeeded in creating new ways to interact with familiar electronic components. Both the buttons and sliders designed for the interface, while maintaining the electronic functionality of the component they are named after, approached their construction in a different way. The DS works well when used by the author, but proves difficult for those unfamiliar with the interface. Especially with the sliders, which look like guitar string and invite users to strum or pluck them, folks struggled to figure out how to interact with the device. That being said, clarity and transparency are not declared tenants of the project and overall the project is considered a success.