"BAUD RATE" of Lidar is "wrong"

[Pito Salas]

I am hooking up my D500 Lidar (aka as Developer Kit, DTOF Laser Ranging Sensor, 360° Omni-Directional Lidar, UART Bus) to my Rasberry Pi 4+ with a USB cable. Looking at the wiki this lidar is also the same as the STL-19P. The speed is supposed to be 230400bps. I am using the "blue" USBs on the Raspi which are supposed to be faster and better.

When I launch the provided node I get this error:

[ldlidar_stl_ros2_node-6] [ERROR] [1753404383.768522930] [ld19]: ldlidar communication is abnormal.

[ldlidar_stl_ros2_node-6] [LDS][INFO][1753404380.767874390][Actual BaudRate reported:230769]

Note that 230,769. is very close to 230,400 which is specced. Not sure if either number is correct though. 

The node concludes that the communication is abnromal and exits.

Have you had this experience or can you help me figure out what might be the matter?

Thanks!

Pito

[Paul Bouchier]

Hi Pito,

You are using an LD19 lidar, which is the same as I am successfully using.

The message about the actual baud rate is a red herring - it's not relevant. The message that lidar communication is abnormal means that the lidar driver was not able to successfully parse a lidar message for 3 seconds. The lidar driver runs a state machine that looks at the incoming data and looks for a header, then a length, then data. If this fails, you get that error. It's possible that you aren't getting any data at all.

Are the blue lights spinning on top of the lidar? If not, you don't have power to it.

Can you put a scope on the data line from the lidar to verify it is sending data?

Can you open the serial port the lidar is using in a terminal program? (Do that before you try and launch the lidar node.) You likely would see stuff coming out.

Is the serial port name correct in the launch file? You likely have two serial ports in use, one for lidar and one for micro-ros. It's easy to get them the wrong way round.

Paul