LW20 altitude or distance sensor

The LW20/C is a laser altitude and distance sensor from LightWare, sold as a 100 m microLiDAR rangefinder for unmanned aircraft and other vehicles. It measures the distance to a surface with a time-of-flight laser and reports the result over a serial UART or I2C interface, which makes it a typical choice for height above ground, terrain following, landing and short-range obstacle detection.

The sensor emits a rapid series of pulses from a 905 nm laser, receives the reflection and processes it immediately. The range is 0.2 to 100 m, specified on a target with 70% albedo in sunlight and a size of 0.9 x 0.9 m. Resolution is 1 cm. Accuracy is plus or minus 5 cm at update rates below 500 readings per second and plus or minus 10 cm above 500 readings per second. The beam divergence is below 0.5 degrees and the optical aperture is 12.7 mm. LightWare states that the measurement is not affected by target colour, texture or the angle of incidence, and that background light, wind and noise have very little influence on it. The laser is Class 1M for eye safety, which means magnifying optics should not be used to view the beam.

The update rate can be selected between 48 and 5000 readings per second. Faster rates suit forward-facing obstacle detection, while slower rates are preferable for scanning. Median, rolling-average and smoothing filters are available: a median filter keeps an altitude hold stable over water or broken ground, a rolling average supports terrain following, and a smoothing filter suits level monitoring. A first-and-last-pulse function reports more than one target in the field of view, which helps measure through foliage or dust. Two alarm outputs signal when an object is closer than distances set by the user.

For integration, the sensor measures 30 x 20 x 43 mm and weighs 19.5 g, and its enclosure is IP67 rated, so it can be mounted outside the airframe. It runs from 4.5 to 5.5 V and draws 85 mA typical, with less than 200 mA at start-up. The interfaces are serial UART and I2C at 3.3 V TTL, 5 V tolerant, plus a servo driver output: a small digital servo can steer the beam for scanning or SLAM mapping. Factory serial settings are 115200 baud with 8 data bits, one stop bit, no parity and no handshaking, and the I2C address is 0x66. A five-way adapter for Pixhawk-type flight controllers is supplied with each unit, and a USB adapter, breakout board and ABS or aluminium mounting brackets are available. Operating temperature is -10 to +50 °C.

The LW20/C is CE certified, RoHS3 compliant, NDAA compliant (Section 848) and Blue UAS listed. Typical applications are altimeter and terrain-following duty on multirotors and fixed-wing drones, automated landing, level and distance measurement, and sense-and-avoid on small autonomous vehicles.