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4

Hysteresis

The algorithm validates a crossing event only when a person has fully crossed the two zones. It does not validate
the event when the person remains for a long time under the FoV or when the person decides to return from the
place he came from.
This is illustrated in the figure below: the algorithm stops and the list of states is reset as soon as no-one is
detected in any of the two FoVs.

Figure 5. 

Hysteresis principle

UM2600

Hysteresis

UM2600

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Rev 2

page 5/15

Summary of Contents for VL53L1X API

Page 1: ...algorithm is provided as an example and can be downloaded from st com in the VL53L1X embedded SW section under the reference STSW IMG010 In addition this document presents the details of a counting application where a sensor is set on the top not the side of the area to be tracked Counting people with the VL53L1X long distance ranging Time of Flight sensor UM2600 User manual UM2600 Rev 2 December ...

Page 2: ...breviations Table 1 Acronyms and abbreviations Acronym abbreviation Definition FoV field of view SPAD single photon avalanche diode SW software ToF Time of Flight UM2600 Acronyms and abbreviations UM2600 Rev 2 page 2 15 ...

Page 3: ...e see figure below and Figure 3 Front and back zones a simple algorithm can detect the direction a person crosses the area under the two FoVs This algorithm understands that someone is under one of the FoV as long as the distance measured by the sensor under this FoV is between 0 and a threshold value specified in mm Figure 1 VL53L1X FoV divided in two subfields of view From a timing perspective t...

Page 4: ...o one is seen in either of the two zones the list of states is reset If we consider that a person detected in the front zone equals 2 and a person detected in the back zone equals 1 the algorithm adds the value of the two states and stores the result as soon as it changes Eventually if the consecutive states in the list are 0 1 3 2 0 or 0 2 3 1 0 this means a person has been detected in one direct...

Page 5: ...t when the person remains for a long time under the FoV or when the person decides to return from the place he came from This is illustrated in the figure below the algorithm stops and the list of states is reset as soon as no one is detected in any of the two FoVs Figure 5 Hysteresis principle UM2600 Hysteresis UM2600 Rev 2 page 5 15 ...

Page 6: ...is recommended to configure the sensor to range alternatively on the two zones every 20 ms Figure 6 Example of configuration of the SPAD array The figure below shows the captured distances from two zones where the VL53L1X is set at 2600 mm from the floor The black arrows correspond to the times when a person was detected entering or exiting the area being tracked Three crossings are visible The fi...

Page 7: ... distances when ranging the floor are greater than this threshold We recommend that at installation of the application an autocalibration routine is launched to calculate the threshold This is because flooring material can be different in many locations Figure 9 Histogram of 3500 measured distances describes an example of such a calibration for the use case illustrated in Figure 8 People counting ...

Page 8: ...the reliability of the setup In Figure 10 Reliable setup the mean of the measured distances from the two zones are the same and equals the real distance between the sensor and the floor which is 2600 mm This indicates a reliable setup Here the threshold is less than 1920 mm Figure 10 Reliable setup UM2600 Ranging on the floor to determine the threshold UM2600 Rev 2 page 8 15 ...

Page 9: ...ection reliability can be checked by running a trimming procedure to adjust the width of the back and front FoVs by enabling the relevant SPADs Analysis of the extracted histograms can help in detecting the SPADs belonging to the parts of the FoVs that do not range on the floor and should never be enabled Note that the smaller the number of lines of SPADs used for this trimming the larger the numb...

Page 10: ...ing to the time when a person is detected only in the first or second zone To optimize the behavior of the algorithm it is advised to choose N as small as possible and to apply a filter on the detected distances which consists of considering only the minimum distance value from the last Z measurements up to the time where a person is detected in the last zone This significantly optimizes the proba...

Page 11: ... person with long black hairshows an example of a fast moving person with long black hair In this case the algorithm does not count the person if the threshold is set with the value corresponding to the red line It is recommended to set a threshold at its maximum possible value but still less than the minimum value reported by the autocalibration as described in Section 6 1 Ranging on the floor to...

Page 12: ...O FR01RE board and X NUCLEO 53L1A1 expansion board To operate Place the device without any object within 2 m in front of the ToF sensor Wave your arm in front of the sensor from left to right and from right to left at a distance 50 cm the people counting result displays as shown in the figure below in Tera term The serial baud rate is set at the 460800 bauds per second Figure 15 Tera term UM2600 S...

Page 13: ...6 1 Ranging on the floor to determine the threshold added new content and figures removed original reliable and unreliable figures Section 6 2 Ensure overlap in the two detection zones removed some text Added Section 7 Example long black hair Section 8 Software and board package removed original content and added to Section 5 VL53L1X sensor and algorithm configuration added new content and moved t...

Page 14: ...53L1X sensor and algorithm configuration 6 6 Setup reliability 7 6 1 Ranging on the floor to determine the threshold 7 6 2 Ensure overlap in the two detection zones 10 7 Example long black hair 11 8 Software and board package 12 Revision history 13 Contents 14 UM2600 Contents UM2600 Rev 2 page 14 15 ...

Page 15: ...cts and ST assumes no liability for application assistance or the design of Purchasers products No license express or implied to any intellectual property right is granted by ST herein Resale of ST products with provisions different from the information set forth herein shall void any warranty granted by ST for such product ST and the ST logo are trademarks of ST For additional information about S...

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