Sonlit

Sonlit Light Show

A sequencer for the lights on your car

Load a track you own, lay lights and closures out on a timeline over its waveform, watch the result play back on a schematic of the car, and export a folder the Model Y will read straight off a USB stick.

Not built yet. The lock sound maker ships first because it is the smallest complete test of the whole phone-to-drive-to-car loop. This tool then arrives in two pieces: a player that imports an existing show and checks and previews it, then an editor for writing one from scratch.

What it will do

The parts of it, in the order they land

The player

Ships first

Import a .fseq file plus its matching audio, both from your own device. Sonlit reads the header, checks it against every rule Tesla publishes, tells you in plain sentences what is wrong if anything is, and plays the show back on the car diagram so you can see it before you ever walk outside. Then it can write the folder back out again.

Reads uncompressed version 2 files at 48 or 200 channels. A 200-channel file made for a Cybertruck opens, and the channels a Model Y does not have are shown as ignored rather than silently dropped.

The editor

Ships after the player

Lanes grouped the way the car is built — headlamps, front lower, sides, rear, closures — over a waveform with a tap-tempo beat grid you can snap to. Left and right pair up on one row with a split toggle and a mirror action, because most of what you want is symmetrical.

On a phone in portrait, a step grid for quick blinks. In landscape, a tap-along recorder: arm it, tap the pads in time with the song, and what you played lands on the timeline as blocks you can then tidy up.

Both halves share the same two guarantees. Your audio is decoded and held in the browser tab and nowhere else — there is no upload in this path at all. And the export is byte-for-byte what Tesla’s documentation describes: a folder named exactly LightShow/ holding lightshow.fseq and lightshow.wav, the audio written at 44.1 kHz because the repository says 48 kHz files will not stay in sync.

Constraints

What the car will and will not let you do

A light show is 48 channels on a 20 ms grid, and roughly half the interesting limits are enforced by the car rather than by the file. Tesla’s own validator checks the header and nothing else, so Sonlit checks the rest and refuses to export a show that will misbehave in your driveway.

The file

Channels
48 (Model Y)
Frame interval
20 ms
Interval range the car takes
15–100 ms
Longest show Tesla allows
4 hours
Longest show Sonlit writes
10 minutes
Audio
44.1 kHz wav or mp3
Default file basename
lightshow

The moving parts

Every closure has a budget the car enforces, counted per show. Go over it and the extra commands are simply ignored, so Sonlit shows the count live on each lane and refuses the one that would break it.

Mirrors
20 commands
Windows
6 each
Liftgate
6
Charge port door
3
Total dancing, recommended
30 s or less

Dancing a closure repeatedly runs into thermal limits. The recommendation is Tesla’s, not mine.

Things that surprise people

  • Most Model Y lights are on or off, not dimmable. Ramping only stretches the turn-on and turn-off; there is no steady half-brightness in between.
  • A light needs at least 15 ms of on-time to emit anything at all, and about 100 ms on and off to read as a flash. Sonlit warns below the second and blocks below the first.
  • Some outputs are wired together. The aux park lights and side markers all share one physical circuit, so they only flash if every one of them is off at the same moment.
  • The doors, the frunk and the door handles do not move on a Model Y. Falcon doors are Model X and pop-out handles are Model S; those channels exist in the format and Sonlit writes zeroes into them.
  • Side markers are fitted to North American cars and the rear fog light to cars outside North America. You pick your market once and the lanes change to match.
  • Test a show somewhere safe. Closures move, and a light show belongs in a driveway or a car park, never on or near a public road.

Today

What is worth doing here now

  1. Read the USB guide

    It is finished and it is the hard part. Getting a folder from a phone onto a flash drive with the exact right name, on a drive the car will accept, is where most attempts fail — and none of it depends on Sonlit existing. Open the USB guide.

  2. Check your car qualifies

    Custom shows need vehicle software 2021.44.25 or newer, and more than one show on a drive needs 2023.44.25. Tap the software version on your touchscreen. If Toybox > Light Show is there, you are set.

  3. Put your name down

    An account is free and takes an email address. Create one and you will hear from me when the player opens, which is also when saved shows start carrying between your browser and, later, the iOS app.

Questions

Things worth knowing before you start

Can I use a song from Apple Music or Spotify?

No. Streaming tracks are protected and a browser cannot open them, so there is no version of this that works with a subscription library. You need a file you actually hold: a purchased download, a recording of your own, a voice memo. The tool will only accept what your device can hand it, and it will say so plainly rather than failing halfway through.

Can I import a show somebody sent me?

Yes, and that is the first half I am building. Give the player a .fseq file and the matching audio and it will parse the header, run every rule Tesla documents over it, and play it back on the car diagram. Compressed files are refused with an explanation — re-export them uncompressed from whatever made them. Sonlit never hosts anyone’s show; the file comes from your device and stays there.

The car says “Light Show” instead of “Custom Light Show”. What did I get wrong?

That exact wording is the car telling you it could not find a valid show on the drive, and it is documented behaviour rather than a bug. Check four things in order: the folder is named LightShow with that capitalisation, at the top level of the drive; the .fseq and the audio file share a basename; the drive has no top-level TeslaCam folder and no map or firmware update files on it; and the drive is exFAT or FAT32 rather than NTFS.

Will it support my Model 3, S, X or Cybertruck?

Eventually, but not at first. Tesla lists Model S from 2021, Model 3, Model X from 2021, Model Y and Cybertruck as able to play a custom show. Sonlit starts with the Model Y from 2020 to 2024 because that is the car sitting in my driveway, and every channel on the diagram is placed from watching that car light up rather than from reading a table. Each further model is a data file, a set of drawings and a day of testing on a real vehicle — so they come one at a time, in that order, and only when I can check them.

When will it actually be ready?

I am not going to give you a date I would have to move. The order is fixed: lock sound, then the shared plumbing, then the light show player, then the editor. Each one goes live when it works on a real car rather than when a calendar says so, and this page changes the day each does.

Acceptable use

  • Use your own recordings or music you have rights to.
  • No public sharing of copyrighted audio through these tools.
  • No use on or near public roads.
  • No automated or bulk use of the storage or email features.

What your car can do depends on its hardware, software version, market and configuration. The drawings on this site are my own stylized diagrams; sources are on the credits page.