The “Ember” is a handheld digital interface modeled on the mbira, a traditional African lamellophone. The driving force behind the Ember’s design was a desire to create a new kind of digital instrument that could be played expressively and not just another knob filled or grid based MIDI controller. Furthermore, the Ember is not just a digitized traditional instrument. The functionality and form of the traditional instrument were used as the point of departure to create a new kind of handheld digital instrument.
The impetus behind the physical design was to create a handheld instrument that allowed for both melodic and continuous control. Being modeled on the mbira, the mechanics of the Ember are directly related to that of a lamellophone, in that the sound is generated from the vibrations of long tongue- like plates that are fixed at one end. A lot of consideration was put into the physical design of the Ember and it has gone through several revisions. Originally it looked very similar to an mbira, other than the fact that it was made of cardboard and had all manner of sensors and wires sticking off of it. However, it became very apparent that the design of the original prototype was cumbersome to hold and to play. A combination of too many sensors and the shape contributed to awkward playing and an inability to hold it steady with one hand. So, a radical redesign was necessary if musical proficiency was to be achieved. First, a method of holding it securely with one hand was needed. The mbira is designed with a hole that the player places their pinky through to support the instrument. So playing on this idea a new body shape was designed that included a hand hole, so that the user’s left hand can fit through it, allowing them to easily and comfortably hold the instrument with one hand. Although this restricts the use of the left hand, it adds a level of stability while playing and frees up the right hand to do other tasks, on or off the instrument. The shape of the body and placement of the handhold were designed to position the two hands at a comfortable angle. This angle allows for ease of play and also promotes prolonged playability by keeping the wrists straight and avoiding awkward or unhealthy wrist positions. Second, the amount of sensors needed to be trimmed down to accommodate the new body shape. In the end, nine piezo powered tines, two membrane potentiometers, and a joystick. The sensors are distributed between the two hand positions; the tines and the membrane pots for the right hand and the joystick for the left. In this setup the left hand becomes responsible for switching functionality, scrolling through lists, or adding expression through the joystick, while the right hand is primarily responsible for melody and continuous control through the tines and the membrane pots. When the shape was set we modeled it using high-density foam to finalize the body size, ergonomic features, and layout. The bridge for the tines was laser cut with rasterized insets to help hold the tines in place and help isolate the vibration of the individual tines. The tines themselves were laser cut out of 1/16” acrylic and don’t actually vibrate like a real mbira. From the first design experiment it was concluded that a stiffer tine allowed for greater control over attack velocity and provided more consistency overall. The final prototype is pictured in figure 5 without the top of the bridge so the piezo films are visible.
For this interface a unique method of using piezo films was developed to simulate the tines of the mbira. Sandwiched between the bridge and the laser cut acrylic, the piezos are safe from accidental triggering while picking up direct hits to their connected tine. When the keys are struck, the piezo picks up the vibration and registers it as a Note On message, even detecting different velocities depending on the pressure applied when played. Due to the body shape and hand positions it is not played like a traditional mbira, instead it is played with one hand, and it seems that striking the tines grants greater control than plucking.
The membrane potentiometers were chosen because they can be controlled with a single finger, allowing the user to manipulate them while playing the tines at the same time. The Ember also includes an analog joystick designed as a utility device, giving the user a kind of “mouse” on board the instrument. However, this simple sensor is also quite useful when used to add expression. The joystick features a button as well, which can be used to change functionality of the joystick itself, or used to cycle through the different harmonic series.
The combination of piezos and membrane potentiometers proved to be quite difficult to work with. Specifically we had to troubleshoot a lot “bleed” across the sensors. We found that the membrane potentiometer would create false readings across the piezos, and sometimes vice versa. We were able to control this contaminating data by a combination of resistors and diodes on the piezos, as well as a bit of Arduino trickery. As we saw the problem to be that the analog to digital buffer was not clearing itself out between analog pin reads, we decided to hook up empty pins to ground and read them in between each sensor. This acted as a sort of flush that rid the circuit of any leftover voltage and solved our data line problems very effectively. At this time a PCB shield is being designed and will hopefully further stabilize the circuit.