Sensing Motion in Performance

We wanted to try out ways of sensing motion during performances and using that to control lights and other aspects of the show. For a percussionist, the most important movements occur at their hand but as they are already holding sticks we needed a wearable solution for motion sensing

I bought a number of different motion sensors, often call IMUs (Inertial Measurement Units) from AliExpress. These little boards include a tiny sensor that would often be used in smartphones or game controllers, on a board just big enough to solder wires and use in prototyping.

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Some of these boards are more powerful, including accelerometers, gyroscopes and digital compass sensors, but this data is a bit more complex to process, so for our prototype performance we chose to use a simpler accelerometer board (ADXL345). I found SparkFun’s hookup guide and library¬†really helpful in getting started with this chip and we soon had a hacked together wireless sensor to experiment with.

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We tried out a few ways of mapping accelerometer data to lights in our development sessions. The most successful so far was to detect “strike” gestures, marked by a sharp increase in aggregated acceleration, and use that to turn on the costume lights. This way, the lighting on Christina’s costume was related to her percussive gestures.

I soldered one of the ADXL sensors to a Wemos D1 Mini board to make a lighter and smaller sensor that we could use in performance:

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In the prototype performance, we just velcro’d this to Christina’s hand and attached a small USB battery to her forearm for power. We could mount her hand LED right on top of the motion sensor. Simple, but worked!

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RGB Light Costume

Today we finished a testing version of our RGB light costume, this is a white shirt with nine LEDs that can be controlled over the wireless network to change colour during the performance.

The current design has four LEDs on each arm of the shirt and a central LED on the micro-controller board. Each LED module is attached to the shirt with velcro so that we can remove the electronics easily.

For this design, we used:

The firmware for the micro controller is here.

Here’s the controller board and one LED module:

Each of the LED modules contains a WS2812 ‘intelligent’ LED that can be controlled by a data signal from a micro-controller. At this point we are controlling all nine LEDs in the costume simultaneously, but they could also be addressed individually to program animations or movement effects.

These lights are surprisingly powerful! We tried out mapping the same pitch-mapped colours as our stage lights to the costume lights which are very convincing from the audience’s perspective!

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Controlling lights wirelessly

One of the first steps for developing our wearable performer system was to control RGB lights wireless over a wifi network. We put together some of our Wemos micro controller boards with some sewable NeoPixels and can now control them over the network! Cool!

In these pictures the colour of the led is controlled from a laptop. We put together a little test program in Pd (pure data) to allow us to control the signals with little sliders, but for the performance we might use physical controllers or control them automatically using sound or movement.

We also realised that the Wemos boards could be easily powered by a regular USB battery pack – just like a smartphone. These are probably the easiest solution for power in the prototyping stage.

The little white case in the photos was a bit of an experiment; at my workplace (UiO Department of Informatics), some of my colleagues are experienced 3D printers, they found a little Wemos D1 case on Thingiverse and printed one out for me! Cool! I think we’ll print out a few more for our prototyping process as they have nice holes for sewing or mounting and could fit a few parts inside – I think we’ll need to adjust the design so that there’s a hole in the side for wires or connectors for the lights.

Building a performer lighting/sensing system

For Synthesthetic, we would like to have a wearable system for showing coloured lights as well as sense movement. This could be attached to the percussionist or dancers and would allow us to use certain movement to affect sound and lights in the piece as well as for the sensation of colour to be applied directly to the performers bodies. In one of our early meetings we developed a system diagram of how this might work for the percussionist.

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More or less, the performer would wear a small battery-powered device that could communicate over a wifi network with a laptop. This device would have a movement sensor and continually send data to the computer. The device would also have a system of small lights that could be controlled remotely from the computer simultaneously with lights on the stage.

I’ve previously had some experience developing a similar system for Last Man to Die in 2010; at that time we used an Arduino powered by AA batteries and a long network cable, later updated to an Arduino Fio. Suffice it to say that the possibilities have changed dramatically since then!

After a bit of research, we settled on the Wemos D1 micro controller platform which includes WiFi on each board and can be powered by USB or a rechargeable battery. These are very inexpensive (about 5USD each) so I bought several to use with different kinds of performers.

For on-body lighting, I found out that you can get integrated RGB LEDs, sometimes called Neopixels, on “sewable” boards! These little guys are about 2cm across and could be sewn onto a costume or lightweight armbands.

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For sensing, I bought a couple of IMUs (Inertial Measurement Units), these are similar to the movement and orientation sensors in smartphones and game-controllers and should allow us to track the performers movements.

Finally, we started assembling some of the Wemos boards and lights to test them out!

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