MysteryLidar
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| 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
Protocol
Serial bit rate is 23400 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
angle
number encoded = 640 + 64*angle, for example