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Jetson Orin / Nano + UART Laser Rangefinder

A Jetson Orin or Nano reads an ERDI laser rangefinder over the 40-pin header UART, usually /dev/ttyTHS1, at 3.3 V logic. Wire TX/RX/GND, free the port from the serial console, add your user to dialout, then read frames with pyserial or run the erdi_lrf_driver ROS 2 node.

Step 1: wire at 3.3 V

The Jetson 40-pin header UART is 3.3 V logic. The module UART must be 3.3 V TTL too; supply voltage is not UART voltage, so check the model page for both rows before connecting, and use a level shifter if the module TX is higher than 3.3 V. Power the module from its own supply as the manual says, with a common ground to the Jetson.

Module Jetson 40-pin header
TX Pin 10 (UART RXD)
RX Pin 8 (UART TXD)
GND Pin 6 (GND)
VCC Own supply per the model manual

Pins 8 and 10 are the standard UART pair on the Jetson 40-pin header; confirm against the carrier-board pinout of your exact developer kit or custom board.

Step 2: find the device name

The header UART is typically /dev/ttyTHS1 on Orin Nano and Nano developer kits, but the name can differ by module and carrier board (for example ttyTHS0). Do not guess:

ls /dev/ttyTHS*
dmesg | grep -i ttyTHS

A USB-TTL adapter shows up as /dev/ttyUSB0 instead, which is the easiest way to bring up a first test.

Step 3: free the port and set permissions

On images where nvgetty runs a login console on the header UART, stop it so it does not consume bytes or echo into the module:

sudo systemctl stop nvgetty
sudo systemctl disable nvgetty

If the service does not exist on your JetPack release, there is nothing to stop; check with systemctl status nvgetty. Then give your user access to the port and log out and in:

sudo usermod -aG dialout $USER
ls -l /dev/ttyTHS1

Step 4: read frames with pyserial

ERDI modules use two UART protocols. Family B (LRF22VB, LRF50VB, H series) free-runs at 460800 baud with 5C lo hi chk frames, check byte = inverse of the sum of the distance bytes, LRF1500H uses a 5-byte frame. Units differ by series: VB series millimetres, H series centimetres. The reader below is a minimal rewrite of the parser in erdi_lrf.py for LRF22VB.

import serial

PORT = "/dev/ttyTHS1"    # confirm with: ls /dev/ttyTHS*
ser = serial.Serial(PORT, 460800, bytesize=8, parity="N", stopbits=1, timeout=0.1)
buf = bytearray()

while True:
    buf.extend(ser.read(64))
    i = 0
    while i <= len(buf) - 4:
        if buf[i] == 0x5C and ((~(buf[i+1] + buf[i+2])) & 0xFF) == buf[i+3]:
            raw = buf[i+1] | (buf[i+2] << 8)       # little-endian
            print("out of range" if raw >= 20000 else "%.3f m" % (raw * 0.001))
            i += 4
        else:
            i += 1
    del buf[:i]

For a polled family A module (for example LRF3000A1, 115200 baud), write the request 55 AA 88 FF FF FF FF 84 and read the 8-byte reply 55 AA 88 STA FF DH DL SUM; STA = 1 means a valid echo and the value is (DH<<8 | DL) x 0.1 m. The ready-made Python package is in erdi-lrf-drivers/python (erdi-lrf --port /dev/ttyTHS1 --model LRF3000A1 measure).

Step 5: ROS 2 with erdi_lrf_driver

Build the package in your workspace, then launch it with the Jetson port (commands from the repository README):

cd ~/ros2_ws/src
git clone https://github.com/ErdiTech/erdi_lrf_driver.git
cd ~/ros2_ws
rosdep install --from-paths src --ignore-src -y
colcon build --packages-select erdi_lrf_driver
source install/setup.bash
ros2 launch erdi_lrf_driver erdi_lrf.launch.py port:=/dev/ttyTHS1 model:=LRF22VB rate:=10.0
ros2 topic echo /range

The node publishes sensor_msgs/msg/Range on range. The full parameter list is on the ROS 2 driver page. Your ROS 2 distribution must match your JetPack/Ubuntu release; see the repository README for the build instructions.

Common pitfalls

Symptom Likely cause Fix
Permission denied on /dev/ttyTHS1 User not in dialout usermod -aG dialout, then log out and in
Stray text or no data nvgetty console on the port Stop and disable nvgetty
Device not found Different UART name on your board ls /dev/ttyTHS*
No frames TX/RX swapped, no common ground Module TX to pin 10, module RX to pin 8
Garbled frames Wrong baud 460800 family B, 115200 family A

FAQ

Is the Jetson UART 3.3 V or 5 V?

The 40-pin header UART is 3.3 V logic. Use a 3.3 V TTL module or a level shifter, and never feed 5 V into the header.

Should I use ttyTHS0 or ttyTHS1?

It depends on the module and carrier board. Run ls /dev/ttyTHS* and check the pinout; ttyTHS1 is the common choice on the 40-pin header of Orin Nano and Nano kits.

Can I use a USB-TTL adapter instead?

Yes. It appears as /dev/ttyUSB0, needs the same dialout permission and the same baud rate, and avoids any serial console conflict.

Where is the frame format for my model?

See the model page at erdilrf.com/models for the frame format and units of your exact model. Questions: tommy@erdimail.com.

Explore knowledge

Category pages: Laser distance sensor · Laser rangefinder module

Models mentioned in this article

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