Use a PCR module to rapidly develop accurate, low-power radar-based sensors
device and Acconeer recommends that they be connected externally on the pc board as well. Intended purely as a radar front-end device, A111 itself stores no firmware permanently, relying instead upon the host microcontroller to upload all sensor software as well as handle A111 sensor initiation, configuration, sweep acquisition and signal processing. Consequently, the choice of companion microcontroller is an important design decision. Acconeer notes that an Arm Cortex-M4-based microcontroller such as STMicroelectronics' STM32L476 or Nordic Semiconductor's NRF52840 is typically sufficient for handling relatively static operations such as distance measurement or basic motion detection. For more dynamic applications such as breathing motion detection or object tracking, Acconeer recommends an Arm Cortex- M7-based microcontroller such as Microchip Technology's ATSAME70. As such, Acconeer pairs the A111 PCR device with an ATSAME70 in its XM112 radar module. The Acconeer XM112 module combines the A111 radar sensor with a Microchip Technology ATSAME70 microcontroller
to provide a complete radar subsystem. Developers can use the XM112 together with the XB112 breakout board to immediately begin evaluating the A111 and building PCR- based software applications. Alternatively, developers can simply plug the 30-pin 24 mm x 16 mm module into their own PCBs to add a self-contained PCR subsystem to their custom designs. To perform radar sensing, developers can control the XM112 module through a serial connection with their development systems or execute software directly on the XM112 host ATSAME70 microcontroller. Software interface Regardless of hardware systems configuration, radar measurements are programmatically controlled using the Acconeer radar system software (RSS) application programming interface (API). The RSS API serves as the sole software interface for working with the A111. Acconeer does not support access to A111 registers through typical SPI transactions due to the complexity of the design, calibration, and processing requirements. Instead, all operations work through the RSS which provides A111 detector functionality. These detectors in turn build on lower level services through APIs for accessing different
and slave select signal (SS) ports. The A111’s ENABLE pin allows developers to use the microcontroller to power up or power down the device, while the INTERRUPT pin allows developers to use the A111 to notify the microcontroller when measurements are ready. By using ENABLE to turn off the A111 between pulse sweep transmissions, developers can reduce A111 power consumption to 66 µA (typical). Conversely, while the A111 performs a series of sweeps and measurements, developers can place the host microcontroller in a low-power sleep state using the wait- for-interrupt (WFI) instruction available in Arm® Cortex®-M- based processors to wake the microcontroller when the A111 completes its operations and issues an interrupt. Designers can add their own precision clock source, or rely on the device’s internal clock circuit which only requires an external crystal oscillator such as EPSON's TSX-3225. The device works with a single 1.8 volt supply for RF (VIO_1 and VIO_2) and digital (VIO_3). Alternatively, developers can use separate supply sources for more power intensive applications. The VIO_Na and VIO_Nb pins shown in Figure 3 are connected within the
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