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Frequently Asked Questions
How do I use the device for fast-scanning
applications?
Using the LIDAR-Lite v3HP device for fast-scanning applications
may require you to change the program you used for continuous
or burst mode functions with previous versions of the sensor.
This method uses slightly more I2C overhead, but it allows more
efficient polling if you know your measurement time, which
depends on maximum acquisition count settings. It also allows
you to know exactly when the measurement begins. With no
other functions running, the device has been able to reach >1.5
kHz with small acquisition count settings.
You can find sample Arduino code for this in the Garmin GitHub
repository at
https://github.com/garmin/LIDARLite_Arduino
_Library.
1
Initiate a new measurement command.
2
Immediately read the distance registers, obtaining the
previous measurement results while the new measurement is
occurring.
NOTE: Measurement data stored in the sensor is valid until a
new measurement concludes.
3
Perform other actions while polling the status bit until it
indicates an idle state.
4
Repeat steps 1 through 3 as needed.
Does the device operate only on 5 Vdc?
The device requires 5 Vdc to function properly.
Connecting the device to a source greater or less than 5 Vdc is
not supported and may result in poor performance or damage to
the device.
What is the spread of the laser beam?
At close distances (less than 1 m), the beam diameter is about
the size of the aperture (lens). For distances greater than 1 m,
you can estimate the beam diameter using the equation
Distance/100 = beam diameter at that distance (in whatever
units you measured the distance). The actual spread is ~8
milliradians (~0.5 degrees).
How do distance, target size, aspect, and reflectivity
affect returned signal strength?
The device transmits a focused infrared beam that reflects off a
target. A portion of that reflected signal returns to the receiver.
You can calculate the distance by taking the difference between
the moment of signal transmission and the moment of signal
reception. Several factors can affect the signal.
Target Distance: The relationship of distance (D) to returned
signal strength is an inverse square. With an increase in
distance, the returned signal strength decreases by 1/D^2 or
the square root of the distance.
Target Size: The relationship of a target's cross section (C) to
returned signal strength is an inverse power of four. The
device transmits a focused near-infrared laser beam that
spreads at a rate of approximately 0.5º as distance increases
(What is the spread of the laser beam?, page
beam overfills (is larger than) the target, the signal returned
decreases by 1/C^4 or the fourth root of the target's cross
section.
Aspect: The aspect of the target, or its orientation to the sensor,
affects the observable cross section. The amount of returned
signal decreases as the angle of incidence to the target
increases.
Reflectivity: Reflectivity characteristics of the target's surface
also affect the amount of returned signal
device work with reflective surfaces?, page
NOTICE
9). When the
(How does the
9).
A small target can be difficult to detect if it is distant, poorly
reflective, and its aspect is away from the normal. In such cases,
the returned signal strength may be improved by attaching
infrared reflectors to the target, increasing the size of the target,
modifying its aspect, or reducing distance from the sensor.
How does the device work with reflective surfaces?
Reflective characteristics of an object's surface can be divided
into three categories.
• Diffuse reflective
(Diffuse Reflective Surfaces, page
• Specular
(Specular Surfaces, page
• Retroreflective
Diffuse Reflective Surfaces
Purely diffuse surfaces are found on materials that have a
textured quality that causes reflected energy to disperse
uniformly. This results in a relatively predictable percentage of
the dispersed laser energy returning to the device. As a result,
these materials tend to read very well.
Some materials in this category are paper, matte walls, and
granite. It is important to note that materials in this category due
to observed reflection at visible light wavelengths may exhibit
unexpected results in other wavelengths. The near infrared
range used by the device may detect them as nearly identical.
For example, a black sheet of paper may reflect a nearly
identical percentage of the infrared signal back to the receiver
as a white sheet of paper.
Specular Surfaces
Specular surfaces are found on materials that have a smooth
quality that reflects energy instead of dispersing it. It is difficult or
impossible for the device to recognize the distance of many
specular surfaces. Reflections off of specular surfaces tend to
have little dispersion, which causes a reflected beam of light to
remain small and possibly miss a receiver altogether. The
device may fail to detect a specular object in front of it unless
viewed from the normal.
Mirrors and glass viewed at large angles of incidence are
examples of specular surfaces.
How does liquid affect the signal?
There are a few considerations to take into account if your
application requires measuring distances to, or within, liquid.
• Reflectivity and other characteristics of the liquid itself
• Reflectivity characteristics of particles suspended in the liquid
• Turbidity
• Refractive characteristics of the liquid
Reflectivity of the liquid is important when measuring distance to
the surface of a liquid or if measuring through liquid to the
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