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LW20 / SF20 LiDAR sensor
Product manual
9. How to set up a scanning LiDAR using a digital servo
The LW20 can be converted into a scanning LiDAR by attaching it to a digital servo and using the built-in servo driver hardware and
software. The LiDAR data can be streamed live or used to activate two internal alarms. This makes a useful SLAM mapping device or
a collision sensor.
The servo driver works with most standard digital servos. Note that analog servos are not compatible as they respond too slowly to
the control signals produced by the LW20. The LW20 is connected to the servo as shown in the diagram below:
Figure 18 :: Servo connections
To reduce the chances of power supply spikes affecting the performance of the LW20, it is important to run the servo from a
separate power supply. Check the servo specifications for the correct voltage and current ratings and make sure that there is a
common connection to the negative rails of the LW20 and servo power supplies.
Communications to the LW20 and the servo can be made through either the serial port or via an I2C bus. In this guide we will use the
serial port and the GUI interface to set up the servo parameters and configure automatic scanning.
Select the "Servo" button under the "Setup" tab to access the initial servo configuration graphic.
Figure 19 :: Setting up the electrical and mechanical characteristics of the servo
With the LW20 connected to the GUI, settings can be entered and saved even without the servo attached. This is useful if you already
know what values to enter for your chosen servo. If the servo is connected, then ticking the "Connected" box and entering settings
through the GUI will result in live movements of the servo, allowing you to see the effect of the new values.
The servo position is controlled by a pulse-width modulated (PWM) signal coming from the blue control line of the LW20. This signal
can change in width from 0us to 3000 us in steps of 0.7us and updates 333 times per second. A given servo will be limited to a
specific range of PWM widths, corresponding to the physical limits of rotary motion.
By default the minimum PWM width is set to 1000 us and the maximum PWM width to 2000 us. This is suitable for most servos but
new values can be entered if needed. If a new value beyond the capabilities of the servo is entered, the servo may draw too much
power, get hot or buzz.
CAUTION: Setting PWM values outside the specified range of the servo may cause damage to the servo.
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LW20 / SF20 LiDAR - Product manual - Revision 7
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© LightWare Optoelectronics (Pty) Ltd, 2018
www.lightware.co.za
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