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I’d like to precisely localize (< 1mm) a robot within a roughly 3m square area.

At first I considered a cheap webcam approach — visual odometry or even just reading linear fiducials (tape measures) with OpenCV — but a friend suggested Valve’s “Lighthouse” positioning system, which looks much more promising. (Also: A great excuse to goof with microcontrollers and analog circuitry.)

These are my research notes. They’re written for my own reference, but feel free to email me if you’re working on a similar project.

Lighthouse tl;dr

The lighthouse system is based on precise timing of near-infrared light pulses. A base station (“lighthouse”) emits a wide field of view sync pulse and then sweeps either a horizontal or vertical beam. A receiver uses the duration between the sync and sweep pulses to determine its horizontal/vertical angular position with respect to the lighthouse. Here’s a great animation:

https://www.youtube.com/embed/oqPaaMR4kY4

Receivers do not need to communicate with the lighthouse, which is just always broadcasting.

The original (1.0) base station can be purchased on Amazon for $130 and a revised (2.0) base station can be purchased from Valve for $149 (or as part of the Vive Pro System for $1,400, if you actually want to play videogames).

The 2.0 base stations have a curved front plate and emit a fancier modulated signal of some kind. Apparently they’re mechanically simpler and allow for combining more lighthouses to create a larger tracked area. See libsurvive for discussion and reverse engineering attempts.

For my project, I’m using the 1.0 base station since there’s more available prior art and the signal looks simpler to decode.

Lighthouse resources

Many people have worked on building open source lighthouse receivers and Alan Yates (the original designer) actively helps on Reddit as /u/vk2zay. Resources that I’ve found most helpful:

• Light Emissions: pulse timing information and binary structure of the OOTX frame that base stations use to broadcast factory calibration parameters (measured offsets from their ideal behavior) and the base station’s gravitational field reading.
• Zippies: adorable robots with open source lighthouse receiver circuit and code for Atmel SAMD21 (ARM32) architecture. When I was first investigating the lighthouse, the Zippies creator confirmed that he is getting sub-mm accuracy, inspired me to pursue my own development.
• Trammel Hudson’s 2016 investigation: Several types of receivers (sensor module, phototransistor, photodiode + transimpedence amplifier) and discussion of math for localization.

First attempt

Triad Semiconductor sells chips for the Valve Lighthouse system:

• TS4112: “Complete Light-to-Digital Sensor with Integrated Photodiode” isn’t yet available (“join our waitlist”)
• TS4231: “2nd Generation Light to Digital Converter (Envelope and Data)” I think maybe only works with Lighthouse 2.0 (it mentions modulated signals) and is packaged as 9 ball pins in a 1.3 mm square, so no way I can solder that by hand.