4.12 Detection thresholds
In addition to the regular ranging capabilities, the sensor can be programmed to detect an object under certain
predefined criteria. This feature is available using the plugin "detection thresholds", which is an option not
included by default in the API. The files called ‘vl53l8cx_plugin_detection_thresholds’ need to be used.
The feature can be used to trigger an interrupt to pin A1 (INT) when conditions defined by the user are met. There
are three possible configurations:
• Resolution 4x4: using 1 threshold per zone (total of 16 thresholds)
• Resolution 4x4: using 2 thresholds per zone (total of 32 thresholds)
• Resolution 8x8: using 1 threshold per zone (total of 64 thresholds)
Whatever the configuration used, the procedure for creating thresholds and the RAM size are the same. For each
threshold combination, several fields need to be filled:
• Zone id: id of the selected zone (refer to Section 2.2 Effective orientation)
• Measurement: measurement to catch (distance, signal, number of SPADs, …)
• Type: windows of measurements (in windows, out of windows, below low threshold, …)
• Low threshold: low threshold user for trigger. User does not need to set the format, it is automatically
handled by the API.
• High threshold: high threshold user for trigger. User does not need to set the format, it is automatically
handled by the API.
• Mathematic operation: only used for 4x4 – 2 threshold combinations per zone. The user can set a
combination using several thresholds in one zone.
4.13 Interrupt autostop
The interrupt autostop feature is used to abort the ranging session during a measurement. By default, the sensor
cannot be stopped during a measurement, because the frame measurements need to be completed. However, by
using autostop, the frame measurements are aborted when an interrupt is triggered.
The autostop feature is useful when it is combined with a detection threshold. When a target is detected, the
current measurement is automatically aborted. Autostop can be used in a customer state machine to switch
quickly to another sensor configuration.
An interrupt autostop feature can be enabled by using the function vl53l8cx_set_detection_threshold_auto_stop().
After a measurement is aborted, it is recommended to stop the sensor by using the function
vl53l8cx_stop_ranging().
4.14
Motion indicator
The VL53L8CX sensor has an embedded Firmware feature allowing motion detection in a scene. The
motion indicator is computed between sequential frames. This option is available using the plugin
‘vl53l8cx_plugin_motion_indicator’.
The motion indicator is initialized using the vl53l8cx_motion_indicator_init() function. If the user wants to
change the sensor resolution, he must update the motion indicator resolution using the dedicated function:
vl53l8cx_motion_indicator_set_resolution().
The user may also change the minimum and maximum distances for detecting motion. The difference between
the minimum and maximum distances cannot be greater than 1500 mm. By default, distances are initialized with
values between 400 mm and 1500 mm.
Results are stored in the field ‘motion_indicator’. In this field, the array ‘motion’ gives a value containing the
motion intensity per zone. A high value indicates high motion variation between frames. A typical movement
gives a value between 100 and 500. This sensitivity depends on the integration time, target distance, and target
reflectance.
An ideal combination for low power applications is the use of the motion indicator with Autonomous ranging mode,
and detection thresholds programmed on the motion. This allows detection of movement variations in the FoV
with minimum power consumption.
UM3109
Detection thresholds
UM3109 - Rev 1
page 13/20
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