Acconeer A121 User manual

A121 Touchless Button Reference
Application User Guide
User Guide

A121 Touchless Button Reference Application User Guide
A121 Touchless Button Reference Application User Guide
User Guide
Author: Acconeer AB
Version:a121-v1.4.0
Acconeer AB November 20, 2023
© 2023 by Acconeer AB - All rights reserved Page 2 of 13

A121 Touchless Button Reference Application User Guide
Contents
1 Acconeer SDK Documentation Overview 4
2 Touchless button 5
2.1 MeasurementRangeandPresets ....................................... 5
2.2 Configuration ................................................. 5
2.3 Calibration .................................................. 5
2.4 Processing................................................... 6
2.5 Results..................................................... 6
2.6 GUI ...................................................... 6
2.7 Tests...................................................... 7
3 Memory 12
3.1 Flash...................................................... 12
3.2 RAM ..................................................... 12
4 Power Consumption 12
5 Disclaimer 13
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A121 Touchless Button Reference Application User Guide
1 Acconeer SDK Documentation Overview
To better understand what SDK document to use, a summary of the documents are shown in the table below.
Table 1: SDK document overview.
Name Description When to use
RSS API documentation (html)
rss_api The complete C API documentation. - RSS application implementation
- Understanding RSS API functions
User guides (PDF)
A121 Assembly Test Describes the Acconeer assembly
test functionality.
- Bring-up of HW/SW
- Production test implementation
A121 Breathing
Reference Application
Describes the functionality of the
Breathing Reference Application.
- Working with the Breathing
Reference Application
A121 Distance Detector Describes usage and algorithms
of the Distance Detector. - Working with the Distance Detector
A121 SW Integration
Describes how to implement each
integration function needed to use
the Acconeer sensor.
- SW implementation of
custom HW integration
A121 Presence Detector Describes usage and algorithms
of the Presence Detector. - Working with the Presence Detector
A121 Smart Presence
Reference Application
Describes the functionality of the
Smart Presence Reference Application.
- Working with the Smart Presence
Reference Application
A121 Sparse IQ Service Describes usage of the Sparse IQ
Service. - Working with the Sparse IQ Service
A121 Tank Level
Reference Application
Describes the functionality of the
Tank Level Reference Application.
- Working with the Tank Level
Reference Application
A121 Touchless Button
Reference Application
Describes the functionality of the
Touchless Button Reference Application.
- Working with the Touchless Button
Reference Application
A121 STM32CubeIDE
Describes the flow of taking an
Acconeer SDK and integrate into
STM32CubeIDE.
- Using STM32CubeIDE
A121 Raspberry Pi Software Describes how to develop for
Raspberry Pi. - Working with Raspberry Pi
A121 Ripple Describes how to develop for
Ripple.
- Working with Ripple
on Raspberry Pi
XM125 Software Describes how to develop for
XM125. - Working with XM125
XM126 Software Describes how to develop for
XM126. - Working with XM126
I2C Distance Detector Describes the functionality of the
I2C Distance Detector Application.
- Working with the
I2C Distance Detector Application
I2C Presence Detector Describes the functionality of the
I2C Presence Detector Application.
- Working with the
I2C Presence Detector Application
Handbook (PDF)
Handbook
Describes different aspects of the
Acconeer offer, for example radar
principles and how to configure
- To understand the Acconeer sensor
- Use case evaluation
Readme (txt)
[README Various target specific information
and links - After SDK download
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A121 Touchless Button Reference Application User Guide
2 Touchless button
The purpose of the touchless button reference application is to employ the A121 sensor as a contactless button. This
algorithm proves useful in scenarios where registering a button press is needed without physically touching a surface. A
prime example would be in public spaces.
Moreover, the algorithm is designed to automatically recalibrate itself when static objects obstruct the sensor, preventing
prolonged and erroneous detections. An initial calibration of the background is performed before starting to detect button
presses. As long as no presses are detected the background will be continuously updated. If a button press is detected
for a long period of time ( calibration_interval_s seconds), the background will be reset since this is considered a
change in the environment. If the initial calibration is done with something in front of the sensor, this will most likely
cause false detects when removed, but the calibration will be reset and a new calibration will be performed. The algorithm
is very dynamic to be able to adapt to changes in the environment.
2.1 Measurement Range and Presets
The reference application is designed to have two different detection ranges: one in close proximity to the sensor and
another farther away. Users can choose which range, or even both, to activate simultaneously.
The close range is defined as the zone from the sensor up to 5 centimeters, while the far range spans from the sensor to
roughly 24 cenitmeters. These ranges are presented in three preset configurations within the Exploration Tool: one for
exclusive close range detection, another for exclusive far range detection, and a third for detecting in both ranges.
It’s important to note that the algorithm can also accommodate extended ranges, provided the sensor settings are
appropriately adjusted to encompass a larger distance.
2.2 Configuration
Each detection range is composed of a single subsweep, allowing for independent configuration and adjustment of each
range.
The measurement_type processing parameter is used to activate a specific range and set which patience and sensitivity
processing parameters to apply during the processing.
The sensitivity parameters ( sensitivity_close and sensitivity_far ) establish the detection threshold for each
range. Meanwhile, the patience parameters ( patience_close and patience_far ) dictate the consecutive frame count
above the threshold required to recognize a button press, as well as the consecutive frames below the threshold to signify
the end of a button press action.
2.3 Calibration
Each subsweep is comprised of multiple points ( num_points ), with each point corresponding to a distance in space where
reflected pulses are measured. These points undergo continuous individual calibration. The threshold is normalized for
each point by evaluating the standard deviation in the number of sweeps received during the calibration_duration_s
period. This threshold normalization remains dynamically updated as long as no detections occur within any range.
Consequently, there might be slight variations in the processor result when both ranges are simultaneously active compared
to their separate activation on the same data.
To change the calibration to include more or fewer frames, the configuration parameter calibration_duration_s
should be increased or decreased respectively. Note that during the calibration no button press actions should be performed
since the purpose of the calibration is to record the background noise.
The calibration_interval_s configuration parameter establishes the maximum time interval in seconds between
successive calibrations. When a consecutive detection reaches the time limit set by calibration_interval_s , a fresh
calibration is initiated. The purpose of the parameter is to adjust the normalization of the detection threshold to
effectively respond to significant environmental changes, such as the introduction of static objects within the detection
range. Therefore, calibration_interval_s should not be set lower than the estimated duration of the longest
continuous detection event.
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A121 Touchless Button Reference Application User Guide
2.4 Processing
For every frame, the processor evaluates whether the sweeps significantly surpass the threshold or not. In the selected
range or ranges, a frame is recorded as significant when a minimum of two sweeps at the same distance surpass the
threshold within the same frame. The patience settings ( patience_close and patience_far ) dictate the number
of consecutive significant frames needed for the event to be deemed as a valid detection (button press). Similarly, it
specifies the number of consecutive frames required to be nonsignificant to signal the end of a detection event. Increasing
the patience setting results in the button detecting prolonged presence in front of the sensor, consequently reducing its
responsiveness. However, it decreases the risk of false detections if short sporadic noise appears.
Since the data from the A121 sensor is complex, each data point includes both phase and amplitude information. The
threshold takes advantage of both the real and imaginary part of the data and can be seen as an circular boundary in the
complex plane. A data point can pass the threshold by either a shift in phase (which would be caused by movement), a shift
in amplitude (which would be caused by a more reflecting object) or both at the same time. Which in turn will trigger a
detection. The placement of the circular boundary in the complex plane is determined by the mean and standard deviation
of the calibration frames measured during the time set by calibration_duration_s and the radius of the boundary is
set by the sensitivity parameters ( sensitivity_close and sensitivity_far ). Opting for a high sensitivity setting
results in a smaller radius, leading to a lower threshold. Conversely, a low sensitivity setting produces a larger radius,
subsequently yielding a higher threshold.
2.5 Results
The algorithm will provide six different results, three for each range: detection, threshold and detection score.
The result parameters detection_close and detection_far will simply declare if there is detection within the range.
The parameters will be True for detection, False for no detection and None if the range is not activated.
The detection scores parameters will provide the detection score for each point in each subsweep. The output shape will
therefore be ( sweeps_per_frame , number of points in current subsweep). The detection score will be None if the range
is not activated.
The parameters threshold_close and threshold_far gives the threshold to which the detection scores are compared
against. The thresholds are inversely proportional to the sensitivity parameters where threshold_close = 10 /
sensitivity_close and threshold_far = 10 / sensitivity_far .
2.6 GUI
In the GUI two plots are displayed, see Figure 1. The top plot shows the detection duration for the close and far range.
The displayed range can be changed by switching the Range parameter under Processor parameters in the GUI or switch
preset under Preset Configurations.
The bottom plot displays the detection score for each distance point in each range. To hide thresholds or points click on
the corresponding symbol in the legend. The points represent the 2nd highest detection score per frame for each distance.
The 2nd highest score is chosen for plotting since a frame counts as significant after two points at the same distance
pass the threshold during the same frame. A detection in the activated range(s) will be shown in the top plot when the
consecutive number of points above the threshold is greater or equal to the patience parameter for the activated range(s).
The purpose of the bottom plot is to demonstrate the effect of the sensitivity settings and to give the user an idea of which
points are most important for the user’s detection scenario. The sensitivity settings might need to be adjusted depending
on integration and purpose of the application. The sensitivity will always result in a trade-off between missed detections
and false detections.
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A121 Touchless Button Reference Application User Guide
Figure 1: Example of the touchless button GUI. Detection is found in both the close and far range. The threshold for each
range and the detection score for each distance is shown in the lower plot.
2.7 Tests
The following section presents the results from various tests on the algorithm.
Presets range test
The purpose of this test was to check that no detections are made outside the appointed range for each preset. Close range
should not have detections outside 0.05 m and far range should not have detections outside 0.24 m.
Test setup
For this test an A121 EVK (XC120 + XE121) was used. To test the presets a corner reflector was moved just outside the
edge of the appointed ranges (0.05 m and 0.24 m), see Figure 2.
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A121 Touchless Button Reference Application User Guide
Figure 2: Test setup to test preset ranges, to ensure no detection outside the range.
Configurations
The configurations below corresponds to the presets in Exploration Tool, see Table 2.
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A121 Touchless Button Reference Application User Guide
Table 2: Touchless button configurations.
Parameter Close range Far range
Sensitivity 1.9 2.0
Patience 2 2
Calibration duration 0.6 s 0.6 s
Calibration interval 20.0 s 20.0 s
Sweeps per frame 16 16
Sweep rate 320 Hz 320 Hz
Inter sweep idle state Ready Ready
Inter frame idle state Ready Ready
Continous sweep mode True True
Double buffering True True
Start point 0 0
Number of points 3 3
Step length 6 24
HWAAS 40 60
Profile 1 3
Results
No detection outside any of the ranges.
Persons test
The algorithm was tested on 10 different people to evaluate the functionality of the algorithm.
Test setup
For this test an A121 EVK (XC120 + XE121) was used integrated with a blinkstick to give the user direct response on
their action. The setup was encapsulated in a 3D-printed cover. No lens was used. See Figure 3.
10 different people were asked to perform a tap with the back of their hand/fingers towards the sensor, as if they were
tapping a button to open a door on for example a buss or a train. The action counted as detected if either or both of the
ranges (close range and far range) detected the action.
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A121 Touchless Button Reference Application User Guide
Figure 3: Shows the setup and action used in the persons test.
Configurations
This test utilized the “Close and far range” preset in Exploration Tool. This preset uses two subsweeps, the subsweep
configurations can be seen in Table 2.
Results
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A121 Touchless Button Reference Application User Guide
Table 3: Results from persons test.
Number of detections Number of actions
Person 1 10 10
Person 2 10 10
Person 3 10 10
Person 4 10 10
Person 5 10 10
Person 6 10 10
Person 7 10 10
Person 8 10 10
Person 9 10 10
Person 10 10 10
Comments regarding changes in temperature
Changing temperature will affect the SNR of the signal. At lower temperatures the SNR is increased and at higher
temperatures the SNR is decreased. Some actions will therefore trigger detection easier at lower temperatures and the
sensitivity can threrefore be set lower at these termperatures. It is therefore favorable to set the sensitivity according to
the desired responsiveness at the highest estimated temperature for the intended integration. The sensitivities selected for
the presets were chosen to minimize missed detections and false detections in the range -10°C and 50°C. The evaluation
was made using 8 different sensors at three different temperatures: -10°C, 25°C and 50°C.
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A121 Touchless Button Reference Application User Guide
3 Memory
3.1 Flash
The reference application compiled from ref_app_touchless_button.c on the XM125 module requires around 73 kB.
3.2 RAM
The RAM can be divided into three categories, static RAM, heap, and stack. Below is a table for approximate RAM for
an application compiled from ref_app_touchless_button.c.
RAM Size (kB)
Preset Close Far Close and Far
Static 1 1 1
Heap 7 7 10
Stack 3 3 3
Total 11 11 14
4 Power Consumption
Average current Current (mA)
Preset Close Far Close and Far
68 68 70
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A121 Touchless Button Reference Application User Guide
5 Disclaimer
The information herein is believed to be correct as of the date issued. Acconeer AB (“Acconeer”) will not be responsible
for damages of any nature resulting from the use or reliance upon the information contained herein. Acconeer makes no
warranties, expressed or implied, of merchantability or fitness for a particular purpose or course of performance or usage
of trade. Therefore, it is the user’s responsibility to thoroughly test the product in their particular application to
determine its performance, efficacy and safety. Users should obtain the latest relevant information before placing orders.
Unless Acconeer has explicitly designated an individual Acconeer product as meeting the requirement of a particular
industry standard, Acconeer is not responsible for any failure to meet such industry standard requirements.
Unless explicitly stated herein this document Acconeer has not performed any regulatory conformity test. It is the user’s
responsibility to assure that necessary regulatory conditions are met and approvals have been obtained when using the
product. Regardless of whether the product has passed any conformity test, this document does not constitute any
regulatory approval of the user’s product or application using Acconeer’s product.
Nothing contained herein is to be considered as permission or a recommendation to infringe any patent or any other
intellectual property right. No license, express or implied, to any intellectual property right is granted by Acconeer
herein.
Acconeer reserves the right to at any time correct, change, amend, enhance, modify, and improve this document and/or
Acconeer products without notice.
This document supersedes and replaces all information supplied prior to the publication hereof.
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