SPD1200N4 UART protocol and integration

SPD1200N4 905 nm Laser Ranging Module

Typical applications: Night vision, Thermal imaging, Civil optics.

Price and buy on erdilrf.comRequest STEP file

At a glance

Protocol family	Family A (55 AA, polled)
Default baud	115200 bps, 8N1
Frame	8 bytes
Distance unit on the wire	metres x 10
Measurement range (datasheet)	see specification

Specification

Values come from the ERDI datasheet for this model. Where the datasheet gives a condition, it is shown.

Parameter	Value	Condition
Laser wavelength	905 ± 5 nm
Ranging accuracy	±0.3 m (≤100 m) · ±0.3 m + D×0.7‰ (100–1,200 m)
Measurement frequency	On request
Interface	UART-TTL	Customizable
Supply voltage	3.3–5 V
Dimensions	On request
Weight	On request
Protection rating	On request
Laser safety class	On request
Operating temperature	On request
Ranging distance	0.2–1,200 m	Strong sunlight or low visibility may reduce range

Pinout and wiring

The pin table for this exact variant is in the model datasheet (see Resources). The connector and wire specification is in the specification table above.

Cross TX and RX (module TX to host RX), share ground, and power the module from a supply that matches the supply voltage in the specification table. See Wiring and power.

Protocol summary

• Frame: 8 bytes, header 55 AA, then function code, four data bytes, checksum.
• Default baud: 115200 bps, 8 data bits.
• Transmit checksum: lower 8 bits of function code + D1..D4 (the header is not included).
• Reply checksum: lower 8 bits of header H + header L + function code + D1..D4 (the header is included). The two formulas differ on purpose.
• Reply to a ranging command: 55 AA <fn> STA FF DIS_H DIS_L SUM. STA = 1 means the measurement succeeded.
• Distance: DIS_H:DIS_L is the measured value in metres multiplied by 10.

Command	Request frame
Single-shot ranging	55 AA 88 FF FF FF FF 84
Continuous ranging	55 AA 89 FF FF FF FF 85
Stop ranging	55 AA 8E FF FF FF FF 8A
Angle measurement	55 AA 8A FF FF FF FF 86

The full frame description is in Family A protocol. Try it without installing anything in the browser serial monitor.

Code examples

Python

pip install erdi-lrf   # PyPI, MIT
erdi-lrf --port /dev/ttyUSB0 --model SPD1200N4 measure

from erdi_lrf import ErdiLRF

with ErdiLRF("/dev/ttyUSB0", "SPD1200N4") as lrf:   # COM3 on Windows
    r = lrf.measure()                          # single-shot (0x88)
    print(f"{r.metres:.3f} m", "raw", r.raw)

Arduino

#include <ErdiLRF.h>

ErdiLRF lrf(Serial1, ERDI_SPD1200N4);

void setup() {
  Serial.begin(115200);
  Serial1.begin(erdiDefaultBaud(ERDI_SPD1200N4));   // 115200 baud; ESP32: Serial1.begin(baud, SERIAL_8N1, RX_PIN, TX_PIN)
  lrf.setTimeout(1000);
}

void loop() {
  ErdiMeasurement m;
  if (lrf.measure(&m) == ERDI_OK) {
    Serial.println(m.metres, 3);
  }
  delay(200);
}

ESPHome

external_components:
  - source: github://ErdiTech/erdi-lrf-home-assistant
    components: [erdi_lrf]

uart:
  id: lrf_uart
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 115200

sensor:
  - platform: erdi_lrf
    uart_id: lrf_uart
    model: SPD1200N4
    name: "Laser distance"
    update_interval: 1s

ROS 2

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/ttyUSB0 model:=SPD1200N4 rate:=10.0
ros2 topic echo /range

Platform status

Only rows with evidence say Verified. See the compatibility matrix for what that means and where the evidence is.

Platform	Status	Guide
Python (erdi-lrf)	Untested	Python / Raspberry Pi / Jetson
Arduino / PlatformIO	Untested	Arduino / PlatformIO
ESPHome / Home Assistant	Untested	ESPHome
ROS 2	Untested	ROS 2
ArduPilot (Lua script)	Untested	ArduPilot
ArduPilot native driver	No driver yet	ArduPilot

Known issues

• The datasheet states that request and reply checksum scopes differ but does not print the transmit formula. The erdi-lrf driver uses the family A transmit formula, which reproduces every example frame the datasheet does print.
• UART logic level is not stated as a separate field for most models. Supply voltage is not the UART voltage: check the module's TX level against your host before wiring, or ask us.

Resources

• Model page with datasheet download: https://erdilrf.com/models/spd1200n4/
• Datasheet and specification page: SPD1200N4 datasheet and specs
• Interactive 3D view: SPD1200N4 3D viewer
• STEP model: available on request, Request STEP
• Drivers and protocol notes: ErdiTech/erdi-lrf-drivers
• Questions: tommy@erdimail.com, +86 133 0819 5790