MysteryLidar

Project MysteryLidar
Aliexpress Mystery Lidar
Status	In progress
Contact	bertrik
Last Update	2024-08-03

Introduction

I bought a cheap lidar from AliExpress, no guarantees, no datasheets. This page is about understanding it and reverse engineering the protocol

Hardware

Has stickers with the following codes:

• on the side of the plastic casing: data matrix HHCT3B6X9K00863
• on the PCB: data matrix FW0251022426001437
• next to the power/data connector: 2d bar code 20617158

Protocol

Serial bit rate is 230400 bps

From the Aliexpress page:

Baud: 230400; Packet_length=60Bytes (in every ~4ms period)

• B0= 0x55
• B1=0xAA
• B2=0x23
• B3=0x10
• B4+B5=current resolution LSB+MSB
• B6+B7= Start Angle of this packet LSB+MSB
• 16x:
  • B8:B9= Distance LSB+MSB
  • B10= Quality (1 byte only) . . .
• B56+B57= Final Angle of this packet (LSB+MSB)
• B58+B59= CRC

The angle is encoded in steps of 1/64 degree, with a 640 offset.

Some numbers:

• each packet is 60 bytes
• each packet contains 16 measurements
• each packet contains data for 10 degrees
• there are about 35 packets per rotation
• there are about 6 rotations per second

=> 6 rotations/s * 36 packets * 60 bytes = 12960 bytes/s

Example packet:

 55 aa 23 10 ec 59 ac f7 7f 40 cd 7f 40 cc 7f 40 cf 7f 40 c6 7f 40 bf 7f 40 b4 80 40 b9 80 40 ba 80 40 bc 80 40 ba 80 40 b5 80 40 d0 81 40 ca 81 40 c2 82 40 c2 82 40 c8 0e a0 cd 2e

angle

number encoded = 640 + 64*angle, for example