A121 Range Sensor

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A121 Range Sensor
A121-Range-Sensor

Millimeter-wave radar, I2C/UART
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Overview

Introduction

A121 Range Sensor is based on 60 GHz Pulsed Coherent Radar (PCR) technology, enabling human presence and motion detection, and supports high-precision distance measurement. With configurable detection zones and sensitivity parameters, it possesses excellent anti-interference capability. The module integrates an Arm® Cortex®-M4 MCU (STM32L431CBT6), which can function as a standalone unit running user applications directly on the Acconeer RSS, or communicate with an external host via a register command protocol. It features small size, low power consumption, and easy integration, making it suitable for applications such as human presence detection, proximity sensing, non-contact triggering, and vital sign monitoring.

Usage Scenarios

  • Consumer electronics
    • Human presence and motion detection
    • Material classification and object detection
    • Vital sign detection (e.g., breathing, heart rate)
    • Gesture control and non-contact buttons
  • IoT & smart cities
    • Smart parking solutions
    • Liquid level/height monitoring
    • Liquid surface velocity measurement
    • Structural integrity monitoring
    • Pedestrian/people flow counting
  • Industry & agriculture
    • Proximity and distance sensing
    • Vibration measurement
  • Automotive electronics
    • In-cabin monitoring (occupant/status detection)
    • Access control and human-machine interaction (HMI)

Operating Principle

The A121 utilizes Pulsed Coherent Radar (PCR) technology. It transmits ultra-short RF pulses and coherently receives the echoes. By leveraging picosecond-level time resolution, it precisely measures the signal round-trip time, achieving sub-millimeter distance accuracy. Simultaneously, phase information allows it to perceive minute displacements and motion. The pulsed operation mode results in very low average power consumption. The highly integrated chip can achieve a range of up to approximately 23 meters without requiring antenna aperture. Since it uses RF electromagnetic waves, it is unaffected by environmental interference such as light, dust, and noise, making it suitable for small, battery-powered devices with low power requirements. Please click this link to understand the working principle of radar.

A121 Range Sensor 01.jpg

Specifications

Product A121 Range Sensor
Operating Frequency Band 60GHz
Modulation PCR
Power Supply 5V
I/O Level 3.3V
Output Interface USB/UART/I2C
Communication Baud Rate UART: 921.6Kbps
I2C: 100K/400K
Range Resolution 0.03m@25°Profile1
Field of View Horizontal: 53°
Vertical: 65°
Range Accuracy 0.03m@Profile1
Maximum Operating Current 5V 80mA
Ambient Temperature -40 ~ 85℃
Dimensions 39×39mm


Exploration Tool

  • Helps you quickly start testing and evaluating our sensor to meet your use case requirements. It will also guide you to find the optimal sensor settings and assist in fine-tuning the final product's data processing. The following runs on a Windows PC. For Linux, please refer to this link.
  • Click to download the host computer tool
  • Click to download the firmware, which is the firmware for the Exploration Tool by default.

Getting Started

  • Extract the portable_exploration_tool.zip file in a suitable location.
  • Double-click the update.bat script. This update process takes a long time, so please wait patiently. If it fails, check your network connection and run update.bat again.
  • After the update is complete, double-click the run_app.bat script to launch the Exploration Tool application. In the pop-up "Acconeer Exptool Launcher" window, click A121.

A121 Range Sensor portable exploration tool 01.png

  • Connect the module to your computer using a Type-C cable. Find the ports in Device Manager. They are listed under Ports (COM & LPT) as USB-Enhanced -SERIAL-A CH342 and USB-Enhanced -SERIAL-B CH342. If not found, you may need to reinstall the driver
  • When connecting the module to the Exploration Tool application, use the USB-Enhanced -SERIAL-A CH342 port, then click Connect. Once successfully connected, you can proceed with testing. Each test has a documentation link next to it; click to view if you are unsure.

Flashing Firmware

  • Click Flash in the Exploration Tool
    • Select XM125
    • Check the box for Show all devices
    • Select the USB-Enhanced -SERIAL-A CH342 port. You can use online download or a local file
    • Click Flash on the next screen. Follow the prompts to enter boot mode, and the firmware flashing will begin.
    • Done indicates successful flashing.

Firmware Description

  • The A121 Range Sensor provides comprehensive firmware variants, including for the host computer tool, UART, and I2C interfaces, as described below:
  • UART firmware outputs information via the USB-Enhanced -SERIAL-B CH342 port or the serial pins on the board
  • I2C firmware outputs information via the I2C pins and is used in conjunction with the BUSY pin. The slave address defaults to 0x52 and can be adjusted to 0x51 or 0x53 via resistors on the board
  • A121 Range Sensor Firmware
Demo Basic Description
Exploration Tool
acc_exploration_server_a121 Flash this firmware to connect with the Exploration Tool
UART
Getting started
example_bring_up Basic bring-up example for quick start and application development
example_control_helper Control helper example demonstrating basic usage of the control interface
example_detector_distance Basic distance detector example
example_detector_presence Basic presence detector example
example_service Basic Service interface example
Advanced control
example_detector_distance_calibration_caching Distance detection + calibration result caching
example_detector_distance_low_power_hibernate Distance detection with low-power hibernate mode
example_detector_distance_low_power_off Distance detection with low-power off mode
example_detector_distance_with_iq_data_print Distance detection with IQ raw data printing
example_detector_presence_low_power_hibernate Presence detection with low-power hibernate mode
example_detector_presence_low_power_off Presence detection with low-power off mode
example_detector_presence_multiple_configurations Presence detection with multiple configuration switching
example_detector_presence_with_iq_data_print Presence detection with IQ raw data printing
example_service_calibration_caching Calibration caching example in Service mode
example_service_low_power_sensor_disable Service low power: sensor disable
example_service_low_power_sensor_hibernate Service low power: sensor hibernate
example_service_multiple_configurations Service multiple configurations example
example_service_sensor_disable Service: sensor disable
example_service_sensor_hibernate Service: sensor hibernate
example_service_sensor_off Service: sensor off
example_service_subsweeps Service: subsweeps configuration example
Processing
example_processing_amplitude Amplitude processing example
example_processing_coherent_mean Coherent mean processing example
example_processing_noncoherent_mean Non-coherent mean processing example
example_processing_peak_interpolation Peak interpolation processing example
example_processing_static_presence Static presence detection processing example
example_processing_subtract_adaptive_bg Adaptive background subtraction processing example
Troubleshooting
example_diagnostic_test Diagnostic test example for hardware/communication troubleshooting
Reference Apps
ref_app_breathing Breathing detection reference application
ref_app_parking Parking/spot detection reference application
ref_app_smart_presence Smart presence detection reference application
ref_app_tank_level Level/liquid level detection reference application
ref_app_touchless_button Touchless button reference application
Example Apps
example_cargo Cargo utilization and human presence detection reference example
example_hand_motion_detection Example for detecting hand motion or gestures
example_surface_velocity Example for measuring the velocity of a moving surface
example_vibration Example for detecting and analyzing vibration characteristics
example_waste_level Example for measuring waste or material level height
I2C
i2c_distance_detector I2C interface distance detector basic example
i2c_example_cargo I2C interface cargo detection example
i2c_presence_detector I2C interface presence detector basic example
i2c_ref_app_breathing I2C interface breathing detection reference application

Lens Description

  • The reference lenses we provide are made of 3301PA material, featuring a solid monolithic structure design with good mechanical strength and stability. The lens assembly consists of the following key components:

1. Lens Holder

Used to secure the PCB and lens assembly, ensuring the relative positional accuracy between the lens and the chip, thereby improving system assembly stability and consistency.

2. Flat Cover

Primarily used to protect the photosensitive chip surface from scratches or contamination during assembly, transportation, or use. It does not introduce optical distortion to the imaging.

3. Fresnel Zone Plate

Achieves light focusing through phase modulation principles. It effectively reduces lens thickness and weight while maintaining focusing capability, making it suitable for applications with structural height constraints.

4. Hyperbolic Lens

Focuses incident light through refraction principles, effectively improving imaging quality, focusing accuracy, and image clarity of the optical system.

  • Lens Holder

  • Flat Cover

  • Fresnel Zone Plate

  • Hyperbolic Lens

Detection Range

  • Flat Cover

A121 Range Sensor 13-1.jpg

  • Hyperbolic Lens

A121 Range Sensor 14-1.jpg

  • Fresnel Zone Plate

A121 Range Sensor 15-1.jpg

Other Information

  • For information on how to configure the A121 and other parameter descriptions, please click this link.

Dimensions

  • A121 Range Sensor 16.jpg
  • A121-Range-Sensordetails-size.jpg

UART Firmware Usage

  • This section briefly explains the effects and usage of UART firmware. The default baud rate is 921600.
  • To test different functions, you need to flash different firmware. For flashing instructions, refer to the Flashing Firmware section above.

Hardware Connection

  • After flashing the firmware, connect the module to the computer via a Type-C cable. You can view information by selecting the USB-Enhanced -SERIAL-B CH342 port or through the TX pin on the MX1.25 connector.

Getting Started

  • example_bring_up effect:

A121 Range Sensor bring up.png

  • example_control_helper effect:

A121 Range Sensor control helper.png

  • example_detector_distance effect:

A121 Range Sensor distance low power off.png

  • example_detector_presence effect:

A121 Range Sensor presence low power.png

  • example_service effect:

A121 Range Sensor sensor off.png

Reference Apps

  • ref_app_breathing effect:

A121 Range Sensor breathing.png

  • ref_app_parking effect:

A121 Range Sensor parking.png

  • ref_app_smart_presence effect:

A121 Range Sensor smart presence.png

  • ref_app_tank_level effect:

A121 Range Sensor tank level.png

  • ref_app_touchless_button effect:

A121 Range Sensor touch botton.png

Example Apps

  • example_cargo effect:

A121 Range Sensor cargo.png

  • example_hand_motion_detection effect:

A121 Range Sensor hand.png

  • example_surface_velocity effect:

A121 Range Sensor surface.png

  • example_vibration effect:

A121 Range Sensor vibration.png

  • example_waste_level effect:

A121 Range Sensor waste level.png

I2C Firmware Usage

  • This section briefly explains the effects and usage of I2C firmware. The default slave address is 0x52.
  • To test different functions, you need to flash different firmware. For flashing instructions, refer to the Flashing Firmware section above.

Working with Raspberry Pi

Enable Raspberry Pi I2C

  • Enter the command in the Raspberry Pi terminal: sudo raspi-config nonint do_i2c 0

Hardware Connection

To access the Raspberry Pi I2C, refer to the following:
A121 Range Sensor 02.png

Install Library

  • C
git clone https://github.com/WiringPi/WiringPi.git
cd WiringPi/
./build debian
# Proceed to the next step based on the generated filename
sudo mv debian-template/wiringpi_*.*_arm64.deb .
sudo apt install ./wiringpi_*.*_arm64.deb
# Check if the installation was successful (a version number will appear)
gpio -v
  • Python
sudo apt install python-smbus2

Download Demo

cd ~
wget https://files.waveshare.com/wiki/A121_Range_Sensor/A121_Range_Sensor_Demo.zip
unzip A121_Range_Sensor_Demo.zip
cd A121_Range_Sensor_Demo/

Run C Demo

cd ~/A121_Range_Sensor_Demo/Raspberrypi/c/
# Choose the compilation target based on the flashed firmware. Options are:
make A121_APP=BREATHING -B
make A121_APP=CARGO -B
make A121_APP=PRESENCE -B
make A121_APP=DISTANCE -B
#Run the demo
./main
  • The terminal will output the relevant information, as shown below:
    • BREATHING:
    • A121 Range Sensor Rpi C breathing.png
    • CARGO:
    • A121 Range Sensor Rpi C cargo.png
    • PRESENCE:
    • A121 Range Sensor Rpi C presence.png
    • DISTANCE:
    • A121 Range Sensor Rpi C distance.png

Run Python Demo

cd ~/A121_Range_Sensor_Demo/Raspberrypi/python/example
# Choose the compilation target based on the flashed firmware. Options are:
python main.py breathing
python main.py cargo
python main.py presence
python main.py distance
  • The terminal will output the relevant information, as shown below:
    • BREATHING:
    • A121 Range Sensor Rpi Py breathing.png
    • CARGO:
    • A121 Range Sensor Rpi Py cargo.png
    • PRESENCE:
    • A121 Range Sensor Rpi Py presence.png
    • DISTANCE:
    • A121 Range Sensor Rpi Py distance.png

Working with ESP32S3

  • For ESP32S3 environment setup and basic usage, please refer to this link.
  • After setting up the environment, you can connect the sensor and download the Demo

Hardware Connection

  • Refer to the following diagram for connection:

A121 Range Sensor 04.png

Arduino esp32 Demos

  • Navigate to A121_Range_Sensor_Demo\ESP32S3\Arduino\*, where * is the demo corresponding to the firmware. Double-click the .ino file.
  • Select development board:

TOF Laser Range Sensor C 19.png

  • Select the port of the ESP32S3, and then compile and upload it
  • After the upload is completed, open the serial port monitor, and the relevant information will be output, as shown below:
    • BREATHING:
    • A121 Range Sensor Esp32 Arduino breathing.png
    • CARGO:
    • A121 Range Sensor Esp32 Arduino cargo.png
    • PRESENCE:
    • A121 Range Sensor Esp32 Arduino presence.png
    • DISTANCE:
    • A121 Range Sensor Esp32 Arduino distance.png

Micropython Demos

  • Navigate to A121_Range_Sensor_Demo\ESP32S3\micropython. Double-click the .py file corresponding to the firmware.
  • Select development board:

TOF Laser Range Sensor C 26.png

  • Select the port of the ESP32S3, and then run the demo
  • The shell will output the relevant information, as shown below:
    • BREATHING:
    • A121 Range Sensor Esp32 Mpy breathing.png
    • CARGO:
    • A121 Range Sensor Esp32 Mpy cargo.png
    • PRESENCE:
    • A121 Range Sensor Esp32 Mpy presence.png
    • DISTANCE:
    • A121 Range Sensor Esp32 Mpy distance.png

Working with Pico

  • For Pico environment setup and basic usage, please refer to this link.
  • After setting up the environment, you can connect the sensor and download the Demo

Hardware Connection

  • Refer to the following diagram for connection:

A121 Range Sensor 03.png

Arduino Pico Demos

  • Navigate to A121_Range_Sensor_Demo\pico\Arduino\*, where * is the demo corresponding to the firmware. Double-click the .ino file.
  • Select development board:

A121 Range Sensor 06.png

  • Select the port of the Pico, and then compile and upload it
  • After the upload is completed, open the serial port monitor, and the relevant information will be output, as shown below:
    • BREATHING:
    • A121 Range Sensor pico Arduino breathing.png
    • CARGO:
    • A121 Range Sensor pico Arduino cargo.png
    • PRESENCE:
    • A121 Range Sensor pico Arduino presence.png
    • DISTANCE:
    • A121 Range Sensor pico Arduino distance.png

Micropython Demos

  • Navigate to A121_Range_Sensor_Demo\pico\micropython. Double-click the .py file corresponding to the firmware.
  • Select development board:

A121 Range Sensor 07.png

  • Select the port of the ESP32S3, and then run the demo
  • The shell will output the relevant information, as shown below:
    • BREATHING:
    • A121 Range Sensor pico Mpy breathing.png
    • CARGO:
    • A121 Range Sensor pico Mpy cargo.png
    • PRESENCE:
    • A121 Range Sensor pico Mpy presence.png
    • DISTANCE:
    • A121 Range Sensor pico Mpy distance.png

Working with Arduino

  • For Arduino environment setup and basic usage, please refer to this R4 link, R3 is installed by default.
  • After setting up the environment, you can connect the sensor and download the Demo

Hardware Connection

  • Refer to the following diagram for connection:

A121 Range Sensor 05.png

Arduino Demos

  • Navigate to A121_Range_Sensor_Demo\Arduino\*, where * is the demo corresponding to the firmware. Double-click the .ino file.
  • Select development board:

A121 Range Sensor 08.png

  • Select the port of the Pico, and then compile and upload it
  • After the upload is completed, open the serial port monitor, and the relevant information will be output, as shown below:
    • BREATHING:
    • A121 Range Sensor Arduino breathing.png
    • CARGO:
    • A121 Range Sensor Arduino cargo.png
    • PRESENCE:
    • A121 Range Sensor Arduino presence.png
    • DISTANCE:
    • A121 Range Sensor Arduino distance.png

FAQ


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