Lawrence Button

We went through various design iterations, finally settling on a simple giant 36cm wide button (just large enough to fit inside a Pelican 1637 Air case). It has a 20cm deep base, which houses 768 individually addressable ultra-bright RGB LEDs on flexible PCBs, and the control electronics. I wanted the LEDs to be visible from as far around as possible (if playing in a venue with audience on all sides).

Building the button to withstand the rigours of touring (while also being lightweight enough to be checked into hold luggage) was a challenge. The top and bottom plates were CNC machined out of 4mm aluminium, and a custom 3D-printed middle part with M3 heat-set inserts held them together. The middle part has a profile with grooves for cables and to hold the flexible LED PCBs, revolved to an angle of 240 degrees. The LEDs are a few centimetres back from the edge, where a diffuser (made of 3mm translucent acrylic, heated up and bent around a custom CNC’d mould of the correct diameter) fits in a groove to give the impression of one coherent light source. The dome is spun out of 2mm aluminium on a custom 400mm dome mould, welded to another piece of aluminium and a 3D-printed adapter screwed on to attach to the switch mechanism

This leaves a small enclosure inside for the control electronics, power supply, and push-switch mechanism.

The mechanism itself took a while to perfect. The button top needs to come off for transport, but also needs to be sturdy enough not to fly off when hit hard. The first iteration (with a smaller button) had a custom-printed mechanism with four springs and four retaining magnets to give the correct force/travel curve (the magnet gives a simulacrum of a dome switch with some ‘give’) and the revised version, with a larger button, allowed for four giant Cherry MX switch copies with a custom spring to give more upwards force (the dome weighs almost 1kg).

The first iteration of this board had a custom STM32-based sample playback PCB, which would play out 48KHz WAV files on an SD card, and sample-synchronously read back from a text file with hex codes to display on the WS2812 LEDs. The PCB had a daughterboard with two 7-segment displays and buttons to select samples and stop the audio. The PCB was quite space-constrained and also featured XLR line drivers and phantom power fault protection, so all components were surface-mount.

The second iteration was a different design – the band now tours with a dedicated Ableton rig and video wall / lighting rig, so the decision was made to offload audio playback onto Ableton, and output MIDI / input DMX512 to the button to use as a conventional lighting fixture, giving the LD control of colour and intensity. A custom PCB was made to house two Arduino Nanos, one taking care of DMX to WS2812 with optoisolated MAX485 line drivers, and the other a standard DIN MIDI output with noteon/noteoff every time the button was pressed.

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