Lightsaber

Arduino Lightsaber

A lightsaber prop built around an Arduino Nano on a custom PCB. It has a 144-LED blade, sound from a DFPlayer Mini, swing detection with an MPU-6050, a small OLED and two buttons. I built it for a Halloween costume.

The OLED screens, rendered by the firmware's own UI code in a PC simulator.

Hardware

The pin map, bill of materials and the known problems with the V3 board are in docs/hardware.md. The schematic is in hardware/exports. The schematic has mistakes the board inherited; the firmware works around them, so trust the board and docs/hardware.md over the schematic.

The hilt is modelled in Fusion 360 (lightsaber-hilt.f3z), and the printable tube is hilt-tube.stl, which GitHub shows in a 3D viewer.

Building

You need arduino-cli with the arduino:avr core. The sketch has no third-party libraries.

arduino-cli compile -b arduino:avr:nano firmware/lightsaber
arduino-cli upload -b arduino:avr:nano -p COM3 firmware/lightsaber

Nano clones with the old bootloader need arduino:avr:nano:cpu=atmega328old. The build uses about 18 KB of the 30 KB of flash and 42% of RAM. Pins, LED count, current limit and the battery and motion thresholds are in config.h.

Building with -DDEBUG_SERIAL=1 prints swing speed and battery voltage over USB at 115200 baud:

arduino-cli compile -b arduino:avr:nano --build-property "compiler.cpp.extra_flags=-DDEBUG_SERIAL=1" firmware/lightsaber

SD card

pip install numpy
python firmware/tools/build_sd_card.py

This fills firmware/sd-card/ and writes sound_lengths.h. Copy the MP3 and ADVERT folders to the root of a FAT32 micro-SD card. Details and the track list are in firmware/sd-card/README.md.

First run

1. If the screen is upside down, flip it in the menu.
2. Lay the saber still and run CALIBRATE in the menu. This zeroes the gyro. It also happens at power-up if the saber is lying still.
3. Compare the BATTERY page with a multimeter on the cell. If it's off, scale BANDGAP_MV in config.h; the Nano's voltage reference is only accurate to about 10%.

Controls

The menu pages are sound, light, colour, sensitivity, flip, calibrate, battery and exit. Light and colour preview on the blade. The saber retracts by itself after five minutes without movement.

How it works

The blade is rendered per pixel into the LED array, which is the only frame buffer in the sketch. The OLED has none either. The panel is mounted on its side and driven in vertical addressing mode, so one physical column is one 32-pixel row of the portrait screen. Each screen is a function that returns a row as a uint32_t, and the UI streams a few rows per loop() pass.

The LED strip needs interrupts off for about 4 ms per frame, which rules out serial receive. The DFPlayer is therefore driven blind. The hum loops on the main channel, effects play as DFPlayer adverts that pause and then resume it, and the one-shot lengths are compiled in so the firmware can stop them when they end.

The cell feeds the Nano's supply directly, so the supply voltage is the cell voltage. The firmware measures it against the internal 1.1 V reference. Charge level and warnings use the voltage with the blade off, because the strip pulls it down by several tenths of a volt when lit.

Repository

firmware/lightsaber/   the sketch
firmware/sd-card/      sounds for the DFPlayer
firmware/tools/        asset and SD card builders, PC simulator
hardware/kicad/        KiCad 8 project
hardware/fabrication/  gerbers exactly as ordered (V3)
hardware/exports/      schematic PDF, PCB renders
hardware/3d/           hilt model, tube STL, PCB STEP
docs/                  hardware notes, images

The simulator runs the real ui.cpp and blade.cpp on a PC (it needs MSYS2 g++ or MSVC):

python firmware/tools/sim/run_sim.py
python firmware/tools/make_readme_images.py

Blade timelines from the simulator. Time runs left to right and the hilt is at the bottom.

Credits

The blade sounds come from the TeensySF font in the ProffieOS default SD card, by Fredrik Hubinette (CC BY-SA 4.0). The menu and boot sounds are synthesized by the repository's tools.

License

MIT. The sound files are under their own licence, see above.