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KY-008 wrist laser

Status (2026-08-29): LIVE + OPERATOR-PROVEN. Wiring is soldered and the laser is mounted parallel to the wrist camera. The production wall-avoid graph owns GPIO17 through laser-control; the Wrist UI hold-to-fire button and release-to-off behavior passed live operator testing. Native-MJPEG wrist preview is stable at 640×480, 5 fps. Hardware tests passed one 200 ms pulse, six 250 ms flashes, and a recorded ten-flash sequence; every sequence ended with laser state confirmed OFF.

Public write-up: repo README.md. Next work is arm poses and camera/beam targeting calibration.

Config: configs/laser.json. Driver: lib/laser_gpio.py. Supervised test: scripts/test_laser.py.

Wiring

Physical header pins, except where BCM is explicit:

Connection Pi / component
KY-008 VCC and S tied together Pi pin 4, 5 V
KY-008 - 2N3904 collector
2N3904 emitter Pi pin 14, GND
Pi pin 11, BCM GPIO17 2 kΩ resistor → 2N3904 base
Base pull-down 4.7 kΩ base-to-emitter

The 2N3904 is a low-side switch; GPIO17 does not source laser current. On the installed flat-face package, pins were verified as emitter-base-collector from left to right. Recheck the specific transistor datasheet after replacing any component.

The 4.7 kΩ pull-down keeps the transistor off while GPIO17 floats during boot or after the process releases the line. Keep 5 V physically isolated from GPIO17.

Tested software path

LeBot is Ubuntu 24.04. gpiod 2.5.0 is installed in /home/jeff/Marco-Dora/dora-lerobot/.venv. The Pi 5 RP1 controller resolves by label pinctrl-rp1 to /dev/gpiochip4; do not hard-code the chip number.

Dry run—acquire GPIO17 low without firing:

cd /home/jeff/Marco-Dora/dora-lerobot
.venv/bin/python robots/so101/scripts/test_laser.py

Supervised blink test:

.venv/bin/python robots/so101/scripts/test_laser.py \
  --pulse-ms 250 --repeat 6 --interval-ms 250 \
  --confirm LASER-AIMED-SAFELY

The supervised test driver permits only bounded blocking pulses. Config limits each test pulse to 1000 ms, and the test script limits a sequence to 10 seconds.

In the production graph, the UI repeats laser_on while the button is held. laser-control turns off unless a fresh command arrives within 750 ms. Button release, tab/page loss, STOP/cancel, any motion request, node shutdown, and GPIO release all request off; the hardware pull-down covers process death and boot. The server rejects laser-on unless the arbiter is idle, wheel telemetry is stopped, and the wrist preview is fresh.

Live acceptance completed on 2026-08-29:

  • Wrist image remained stable after switching capture from uncompressed YUYV to native MJPEG at 5 fps.
  • Wrist-tab press-and-hold illuminated the mounted laser; release extinguished it.
  • Ten remote 300 ms flashes completed for video, followed by explicit off and /state verification (laser.on=false).

Mounted hardware

The soldered module is in a newly designed wrist-camera mount with the laser axis parallel to the camera. Confirm insulation, strain relief, harness service loops, and full safe joint travel before normal arm motion. Aim only downward into a matte beam stop; avoid eyes, people, pets, glass, mirrors, and polished metal.

Arm pose and aiming work

Follower IDs:

ID Joint Laser role
1 shoulder_pan Horizontal aim
2 shoulder_lift Raised clearance pose
3 elbow_flex Raised clearance pose
4 wrist_flex Vertical aim
5 wrist_roll Camera/laser roll; usually not primary aim
6 gripper Not an aiming joint

Next record STOW and LASER_READY follower positions using teleoperation. LASER_READY must keep the arm out of the forward OAK-D view and constrain the beam below eye level. Keep the laser off during every arm or base movement.

After poses are repeatable:

  1. Calibrate the laser dot relative to wrist-camera pixels at several working distances.
  2. Detect the target in the wrist image and choose an aim pixel or physical offset.
  3. Start with stop-and-align corrections using shoulder pan and wrist flex.
  4. Add a bounded pulse only after wheels are stopped, the safe pose is confirmed, and the target remains valid.
  5. Make phone STOP, cancel, timeout, process exit, and any arm transition force laser off.

The production graph exposes supervised UI-only laser_on / laser_off; it still has no arm actions or DimOS laser skill. Develop arm poses and targeting as a supervised path before exposing autonomous firing.