In the experimental project stage, the concept was not as clearly defined, but the hardware specifications were in hindsight already well advanced. There was a need for a system including a gyro sensor and an accelerometer that could wirelessly transmit data with low latency to a Windows platform directly, or via some sort of hub. This sensor system (including power supply) should have a small enough form factor to fit on a wristband. On the Windows platform the received data would get processed in Pure Data, which in turn controls a composition Ableton Live.
I decided to work with the 2.4SINK Kit by Instruments of Things, which is a set of wireless wristband sensors and a receiver. The receiver is made for modular Eurorack setups, meaning that wristband movements are translated into control voltages (CV’s) that can be used to modulate synthesizers or effect panels. This was of course not necessarily optimal for this application, since all the wristband data was needed in a digital format anyway. Luckily, the module was already built into a small Doepfer box, together with an Expert Sleepers USB Audio Interface, that facilitated up to 10 CV inputs via USB on my laptop.
The sensors looked sturdy, but also thin and subtle. On the backside, each watch had two metal pins that are used to switch the sensor on (if both pins are touched at the same time). Additionally, the pins are used as a mounting contraption to fit them on belt clips or fabric wristbands (“click-mount”). As soon as a sensor got switched on it went into calibration mode, making it important to have the sensor lying still on a flat surface during this process (otherwise the values will drift off constantly).
The receiver consists of an antenna, a little toggle button that switches between “configuration” and “active” mode and 16 dynamically configurable outputs. When switched on, the 2.4SINK receiver will create a wireless LAN network, which, if accessed, will provide the opportunity to visit the configuration page of the 2.4SINK Kit. On the configuration page, it is possible to change a few global settings, as well as individual settings for all 16 outputs (while the switch on the receiver is set to “configuration mode”). For each output, it is possible to choose which parameter of which sensor (up to seven sensors can be connected) should modulate the output. For each sensor, six parameters could be chosen:
- Rotation X
- Rotation Y
- Rotation Z
- Acceleration X
- Acceleration Y
- Acceleration Z
Furthermore, it is possible to output LFO signals that are modulated by the sensor’s parameters. However, this is much more interesting for a modular setup and not very suitable for my use case.
The Expert Sleepers USB Interface (ES8 plus ES6 input expansion module) worked just as most other USB audio interfaces do. The CVs were normalized as input signals ranging from -1 or 0 (depending on the type of input: unipolar/bipolar) to 1.
While there were only two sensors available, the 2.4SINK receiver would have still supported to read out all parameters from both sensors (six plus six parameters, while the receiver features 16 outputs), but the true bottleneck in this case was the Expert Sleepers audio interface, which only has 10 inputs, meaning that not even all parameters from both sensors could be read simultaneously.