ST AEK-SNS-2TOFM1 User manual

Introduction
The AEK-SNS-2TOFM1 evaluation board offers an innovative approach based on Time-of-Flight (ToF) sensors for car power
liftgate applications.
This board represents a more cost-effective and reliable solution compared to the standard "kick under the bumper" solution.
The distance among the on-board sensors has been specifically designed for placement under the car bumper.
The kick gesture is replaced with a more unequivocal foot gesture interpreted by a finite state machine built in the
microcontroller firmware.
The board is designed as a small sensor hub ECU able to retrieve and process real-time sensor data to detect a gesture
performed under the two sensors. Moreover, you can control the board through an external domain controller via a CAN or a
serial interface.
Figure 1. AEK-SNS-2TOFM1 evaluation board
Warning: The AEK-SNS-2TOFM1 is an evaluation tool for R&D laboratory use only. It is not intended to be used
inside a vehicle.
Getting started with the AEK-SNS-2TOFM1 evaluation board for car power
liftgate applications
UM3006
User manual
UM3006 - Rev 1 - May 2022
For further information contact your local STMicroelectronics sales office. www.st.com

1Getting started
1.1 Hardware overview
The following figure shows the AEK-SNS-2TOFM1 top components:
1. 12 V DC-DC connector
2. SPC582B60E1 Chorus 1M automotive-grade microcontroller
3. Successful detection LEDs
4. JTAG connector for microcontroller programming
5. CAN connector
6. Serial connector
Figure 2. AEK-SNS-2TOFM1 components (top view)
3
1
4
25
6
3
The following figure shows the AEK-SNS-2TOFM1 bottom components:
1. VL53L1X Time-of-Flight ranging sensor based on ST FlightSense technology
Figure 3. AEK-SNS-2TOFM1 components (bottom view)
11
The board hosts the SPC582B60E1 automotive microcontroller that belongs to the Chorus family, with a high
performance e200z2 single core 32-bit CPU running at 80 MHz clock, a 1088 KB flash memory, and a 96 KB
SRAM in a compact eTQFP64 package. The microcontroller monitors and controls the two ToF sensors to detect
the foot gesture.
The communication between the microcontroller and the ToF sensors is implemented via SPI. The microcontroller
controls the LEDs on the board top side through two dedicated GPIOs.
The AEK-SNS-2TOFM1 can be remotely controlled through a central ECU via a CAN or a serial interface. For this
reason, a CAN connector and a serial connector are present on the board.
UM3006
Getting started
UM3006 - Rev 1 page 2/38

1.2 Software overview
The AEK-SNS-2TOFM1 board contains a preloaded demonstration firmware. It is ready to be tested.
If you have modified the flash memory code and you want to reinstall the original version, use the SPC5-UDESTK
programmer plugged on the JTAG connector. The source code is included in AutoDevKit 1.6.1 (or higher). Among
other demos, you can find one called “SPC582Bxx_RLA AEK_SNS_2TOFM1_1M_with_CAN_for_footdetection-
Trunk System Control”.
For the detailed upload procedure, refer to Section 3.7
The above-mentioned demo purpose is to detect a specific foot/hand gesture and to inform a domain controller
via a CAN message that the successful detection event has occurred.
The gesture consists in a foot/hand movement from the left to the right and vice versa.
Figure 4. Gesture recognition pattern
The recognition process starts when the gesture crosses at least one of the photon beams emitted by the two ToF
sensors.
The algorithm implemented requires that the gesture has to be performed in one second maximum. If the gesture
is not detected, wait one second before repeating it. When the correct movement is detected, the two on-board
LEDs blink three times.
To work correctly, the demo requires the board to be placed at 132 mm height. Otherwise, the two sensors are
not properly configured during the power-up calibration phase. As soon as the board is turned on, and the system
is correctly initialized, the two on-board LEDs turn on. The two sensors detect the movement of the foot/hand for
distances between 0 and 120 mm. The demo can also receive external CAN messages to turn the ToF sensors
on/off. The detected_foot() is used to implement the gesture algorithm.
When performing the tests outdoor, ensure placing the AEK-SNS-2TOFM1 board as shown in the following figure,
to make the sensor photon beams fall within the car shadow cone.
Figure 5. Board placement
ToF
Car shadow
UM3006
Software overview
UM3006 - Rev 1 page 3/38

1.2.1 Gesture recognition
The gesture consists in crossing the detection base (that is, the distance between the two ToF sensors) in both
directions, as shown in the figure below.
Figure 6. Gesture on the detection base
The algorithm is based on the idea that the foot detection state can have one of the following values:
•0: not detected
• 1: detected by sensor 1 (left-hand side)
• 2: detected by sensor 2 (right-hand side)
Figure 7. Detection system states
A gesture can be represented through a sequence of states. The sequence that represents the gesture of the
figure above is: 0,1,0,2,0,2,0,1,0. The sequence 0,2,0,1,0,1,0,2,0 is also admitted as we want the gesture to start
in the opposite direction, too. The central zeros in the sequence are necessary because a complete crossing of
the detection base is desired. For example, the first admitted sequence is shown in the figure below.
UM3006
Software overview
UM3006 - Rev 1 page 4/38

Figure 8. Accepted sequence
The detect_foot () function, cyclically called by the microcontroller, implements the algorithm.
The foot detection functions can be divided in:
1. System State Detect that detects the state of the system:
– if sensor 1 detects an object, the state becomes 1
– if sensor 2 detects an object, the state becomes 2
– if there is no detection, the state becomes 0
– if both sensors detect something, the state becomes 3
The last value means that there is a fixed object under the trunk (for example, a stone).
2. State Sequence Update that updates the gesture sequence if the state changes.
3. State Sequence Check that compares the detected sequence with those admitted as soon as the
detected pattern reaches a length equal to the SEQ LEN. If there is a match, the function sets a, which is a
global variable representing the achieved foot detection, to 1.
4. System Reset: if the sequence reaches a length equal to the SEQ LEN and there is no match, or a RESET
TIME has elapsed, the system resets and restarts the detection mode.
UM3006
Software overview
UM3006 - Rev 1 page 5/38

2Basic concepts on FlightSense ToF sensors and their usage in
AutoDevKit
2.1 Overview of the FlightSense ToF sensor principle
The Time-of-Flight is a method for measuring the distance between a sensor and an object. It is based on the
time difference between the emission of a light signal and its return to the sensor, after being reflected by the
object.
Figure 9. ToF principle
According to the ToF principle, the sensors used in the AEK-SNS-2TOFM1 embed:
• an emitter that is a vertical cavity surface emitting laser (VCSEL);
• a receiver that is an array of single photon avalanche diodes (SPADs). The photons emitted by the laser
reflect on the target and trigger avalanches when coming back to the SPAD.
The ToF sensor also features a region of interest (ROI) that can be selected. It can be reduced from its nominal
27° field of view (FoV) to 15° with the only condition of having an array of at least 4x4 SPADs.
UM3006
Basic concepts on FlightSense ToF sensors and their usage in AutoDevKit
UM3006 - Rev 1 page 6/38

Figure 10. ToF sensor system FoV: receiver cone at 27°
The ROI selection is used to position the reduced sensing area at a selected place on the SPAD array to detect
and measure the distance of the specified area of interest of the external scene. Instead, the reduced FoV uses a
reduced number of SPADs for the ROI sensing area to limit the viewing angle of the sensor device.
For more information on the VL53L1X, refer to the datasheet, whereas, for more information about the
programmable region of interest (ROI), refer to AN5191.
2.2 VL53L1X
The VL53L1X is a state-of-the-art, Time-of-Flight (ToF), laser-ranging sensor, enhancing the ST FlightSense
product family. It is the fastest miniature ToF sensor on the market. It features an accurate ranging up to 4 m and
fast ranging frequency up to 50 Hz.
Housed in a miniature and reflowable package, it integrates:
• a SPAD receiving array;
• a 940 nm invisible Class1 laser emitter;
• physical infrared filters;
• optics to achieve the best ranging performance in various ambient lighting conditions with a range of cover
glass options.
Unlike conventional IR sensors, the VL53L1X uses ST latest generation ToF technology, which allows absolute
distance measurement independently of the target color and reflectance.
You can also program the size of the ROI on the receiving array, allowing the sensor FoV to be reduced.
Figure 11. VL53L1X ToF
UM3006
VL53L1X
UM3006 - Rev 1 page 7/38

2.2.1 ToF sensor characteristics
The AEK-SNS-2TOFM1 sensor characteristics are:
• a laser wavelength of 950 nm ± 30 nm;
• invisible laser (Class 1);
• invisible laser radiation;
• a maximum laser power emission of 25 mW.
2.2.2 Laser safety considerations
The AEK-SNS-2TOFM1 ToF sensors contain a laser emitter and the corresponding drive circuitry.
The laser output is designed to remain within Class 1 laser safety limits under all reasonable foreseeable
conditions, including single faults, in compliance with the IEC 60825-1:2014 (third edition).
The laser output remains within Class 1 limits as long as you use the STMicroelectronics recommended device
settings and respect the operating conditions specified in the data sheet.
The laser output power must not be increased and no optics should be used with the intention of focusing the
laser beam.
Figure 12. Class 1 laser product label
2.2.3 VL53L1X-SATEL industrial-grade ToF evaluation board
The AEK-SNS-2TOFM1 development is based on the hardware and software provided to evaluate the ToF
sensors. The evaluation board used is the VL53L1X-SATEL. For this board, we have already implemented an
AutoDevKit component named AEK_SNS_VL53L1X.
The demo software for the AEK-SNS-2TOFM1 has been developed by reusing the APIs already available for
the VL53L1X-SATEL. In turn, the VL53L1X-SATEL drivers have been imported from the STM32 drivers just by
customizing the hardware abstraction layer (HAL) calls for the SPC58 family microcontrollers.
The VL53L1X-SATEL breakout compact board can be used for easy integration.
Thanks to the voltage regulator and level shifters, this board can be used in any application with a 2.8 V to 5 V
supply.
UM3006
VL53L1X
UM3006 - Rev 1 page 8/38

Figure 13. VL53L1X-SATEL top and bottom views
The embedded VL53L1X ToF sensor uses the I²C protocol for communication.
The I²C bus on the VL53L1X has a maximum speed of 400 kbits/s and uses a default device address (0x52).
You can connect the VL53L1X-SATEL to an MCU board through different connection types, as shown in the figure
below.
Figure 14. VL53L1X-SATEL connection types
UM3006
VL53L1X
UM3006 - Rev 1 page 9/38

2.2.4 Power up and boot sequence
The ToF sensor has two different options for the power-up and boot sequence:
•Option 1: the XSHUT pin is connected and controlled from the host. This option optimizes the power
consumption as the sensor can be completely powered off when not used, and then woken-up again. The
hardware standby mode is defined as the period when the power supply is present and the XSHUT is low.
Figure 15. Power up and boot sequence
XShut
System state Power off HW standby SW standbyBoot
Power supply
•Option 2: the host does not control the XSHUT pin, which is tied to the power supply through a pull-up
resistor. When the XSHUT pin is not controlled, the power-up sequence starts as shown in the figure below.
In this case, the device goes automatically to software standby after boot, without entering the hardware
standby mode.
Figure 16. Power up and boot sequence with a pull-up resistor
XShut
System state Power off SW standbyBoot
Power supply
Note: The AEK_SNS_VL53L1X component uses option 1. This means that when more than one sensor is
used, each sensor XSHUT pin has to be connected. Then, the host turns the sensor on by using the
AEK_TOF_CONFIG procedure.
UM3006
VL53L1X
UM3006 - Rev 1 page 10/38