LH2 calibration over a serial cable#

The bench alternative to the over-the-air flow: calibrate a single DotBot connected over USB, with no swarm provisioned. Reach for this when you’re working with one DotBot on the bench, or before the fleet is set up. For already-deployed DotBots, prefer the over-the-air flow - no cable, no firmware swap.

What LH2 calibration is, and the arena geometry (the -d square sizing), are covered in the main guide; this page is just the cabled capture path.

Prerequisites#

  • A DotBot v3 you can cable to your machine over USB-C (no external probe - the v3 flashes over its on-board programmer).

  • Two LH2 base stations facing the arena, and a square marked on the floor (see Sizing -d in the main guide).

  • The [calibrate] extra:

pip install 'pydotbot[calibrate]'

1. Flash the capture firmware#

The lh2_calibration app streams raw LH2 counts over serial. Flash it to the cabled DotBot (see device for serial-prefix selection):

dotbot device flash lh2_calibration --probe 77      # board defaults to dotbot-v3

2. Capture the four reference points#

Place the DotBot on the floor square and run the TUI. -d is the side length of the square, in millimeters:

dotbot run lh2-calibration collect -p /dev/cu.usbmodem... -d 500

Move the DotBot to each corner - Top left -> Top right -> Bottom left -> Bottom right - pressing the matching button in the TUI at each. When all four are captured, save. The calibration is written under ~/.dotbot/calibrations/ (a calibration-<UTC>.toml), the same place the over-the-air flow uses.

Flag

Default

Meaning

-p, --port

auto-detect

Serial port of the calibration firmware.

-d, --distance

calibration default

Square side length, in mm.

-n, --extra-lh-num

0

Extra base stations beyond the first (0–5).

--input-data

-

Re-process a saved capture instead of capturing live.

See dotbot run lh2-calibration collect --help for the full list.

3. Use the calibration#

Send the saved calibration to the fleet over the air (the same command the over-the-air flow uses - stop any running app first):

dotbot swarm stop
dotbot swarm lh2-calibration push ~/.dotbot/calibrations/calibration-<UTC>.toml

Bake it into the bootloader (header path)#

For a fresh board whose bootloader bakes the calibration in at compile time (rather than receiving it over the air), export the saved calibration as a C header instead:

dotbot run lh2-calibration apply ./lh2_calibration.h

The swarmit secure bootloader #includes this file; rebuild and reflash the bootloader for it to take effect. For already-running DotBots, prefer the over-the-air push above - no reflash needed.

Troubleshooting#

  • No counts in the TUI - wrong -p port, or the DotBot can’t see both base stations. Confirm line-of-sight and that the base-station LEDs are steady.

  • Positions look skewed or mirrored - the corners were captured out of order. Re-run collect and follow TL -> TR -> BL -> BR exactly.

  • Positions are scaled wrong - -d didn’t match the real square. It’s in millimeters, not centimeters.

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