Send messages between a hub and a bluetooth application.

[gpdaniels]

Desktop app:

• [ ] GUI
• [x] BT connection
• [ ] BLE connection

Android app:

• [ ] GUI
• [x] BT connection
• [ ] BLE connection
• [x] Permissions
• [x] Running in the background

[postpersonality]

Hi! I've investigated this a bit. I have a small dump of a short bluetooth session between Android Robot Inventor and the hub. So far I see it's working via BT, not BLE since it uses RFCOMM. RFCOMM is a part of BT stack.

Here is what I found so far.

Android -> Hub request messages

• {"i":"....","m":"get_hub_info","p":{}}
• {"i":"....","m":"program_modechange","p":{"mode":"play"}}
• {"i":"....","m":"program_terminate","p":{}}
• {"i":"....","m":"reset_program_time","p":{}}
• {"i":"....","m":"scratch.display_animation","p":{"frames":["00900:06960:99099:06960:00900","00900:06960:99099:06960:00900","00900:06960:99099:06960:00900","00900:06960:99099:06960:00900"],"async":false,"delay":500,"fade":5,"loop":false}}
• {"i":"....","m":"scratch.display_clear","p":{}}
• {"i":"....","m":"scratch.display_rotate_orientation","p":{"orientation":"4"}}
• {"i":"....","m":"scratch.motor_go_to_relative_position","p":{"port":"A","position":0,"speed":35,"stall":true,"stop":1}}
• {"i":"....","m":"scratch.motor_pwm","p":{"port":"A","power":50,"stall":true}}
• {"i":"....","m":"scratch.motor_pwm","p":{"port":"A","power":-50,"stall":true}}
• {"i":"....","m":"scratch.motor_run_timed","p":{"port":"A","time":1000,"speed":50,"stall":true,"stop":1}}
• {"i":"....","m":"scratch.motor_set_position","p":{"port":"A","offset":0}}
• {"i":"....","m":"scratch.motor_set_position","p":{"port":"A","offset":73}}
• {"i":"....","m":"scratch.motor_start","p":{"port":"A","speed":80,"stall":true}}
• {"i":"....","m":"scratch.motor_start","p":{"port":"A","speed":-80,"stall":true}}
• {"i":"....","m":"scratch.motor_stop","p":{"port":"A","stop":1}}
• {"i":"....","m":"scratch.play_sound","p":{"path":"/extra_files/Hydraulics Up","volume":10,"freq":16000,"wait":false}}
• {"i":"....","m":"scratch.reset_yaw","p":{}}
• {"i":"....","m":"scratch.ultrasonic_light_up","p":{"port":"F","lights":[0,0,0,0]}}
• {"i":"....","m":"scratch.ultrasonic_light_up","p":{"port":"F","lights":[100,100,100,100]}}
• {"i":"....","m":"trigger_current_state","p":{}}

Description of the request message

• i — Random message ID (consists of 4 chars from range: 0-9, a-z, A-Z, -, _) this is needed for identification of response message from the hub
• m — Command to be executed. This is mapped to the methods inside commands/* of the filesystem of the hub. The methods begin with handle_....
• p — Object with parameters specific to a command

Hub -> Android status messages

• {"m":0,"p":[
  • [75, [0, 0, 179, 0]], // Port A (state of a motor)
  • [0, []], // Port B
  • [0, []], // Port C
  • [0, []], // Port D
  • [0, []], // Port E
  • [0, []], // Port F
  • [-8, 0, 1021], // compass
  • [6, 10, -5], // acceleration
  • [0, 0, 0], // z rot, long side incline, short side incline
  • "",
  • 9932]}
• {"m":2,"p":[8.323, 100, false]} // Battery status message, sent once a second
• {"m":4,"p":"down"} — event when hub gets flipped to a side
• {"m":4,"p":"doubletapped"}

[pizzakid25]

I found a few additional commands I thought might be useful:

• {"i":"....","m":"program_execute","p":{"slotid": 1}} - Starts program saved to slot 1.
• {"i":"....","m":"program_terminate","p":{}} - Stops currently running program.
• {"i":"....","m":"get_storage_status","p":{}} - Returns current storage and slot information.
• {"i":"....","m":"move_project","p":{"old_slotid": 1, "new_slotid": 2}} - Moves program from slot 1 to slot 2.
• {"i":"....","m":"remove_project","p":{"slotid": 1}} - Deletes program from slot 1.

[brabebhin]

Hi. Does sending these commands work with the factory firmware or do I have to flush something custom?

I have a research project using these 51515 hubs as targets, and I have been looking for a way to control them through a desktop application without the need of LEGO app.

[pizzakid25]

@brabebhin These commands work with the default firmware over Bluetooth or USB. Most commands should work for both 51515 and Spike hubs, but there might be a few that are system-specific since the firmware varies slightly.

[brabebhin]

Cool thank you for the information. One more question: i know in older lego sets the serial message had to be prefixed with the length of the message, does this apply here as well?

Thanks