Mainboard PCB for the Ambient project.

For more details, please refer to the mainboard Git repository and the Ambient project README.

Overview

The Ambient project strives to provide a biodiversity monitoring platform built around an autonomous smart sensor node deployed in the wild.

Currently, the project focuses on birdsong recording and recognition for bird species classification.

The hardware and firmware project sources are provided as open-source (hardware: CERN-OHL-P-2.0 license, software: Apache-2.0 license) for anyone to build, improve and extend the platform.

In addition to the mainboard, also provided under open-source licenses are:

• Antenna PCB
• Audio capture and energy management daughterboard
• Zephyr-based firmware
• Arduino-based firmware

Main features of the mainboard

• Microcontroller from the STM32L4 or STM32U5 families (LQFP-64 package, no SMPS):
• STM32L496RG: low-power, Cortex-M4F 80 MHz, 320 KiB SRAM, 1 MiB Flash
• STM32U595RI: ultra-low-power, Cortex-M33 160 MHz, 2.5 MiB SRAM, 2 MiB Flash
• LoRa modem (Ebyte E22-900M22S)
• GNSS module (Quectel L96-M33)
• Temperature, humidity and pressure (Bosch BME280)
• Micro-SD card reader

The design also provides empty footprints for several other sensors which are not populated in the Ambient variant:

• Light sensor (LITEON LTR-303ALS-01)
• MEMS microphone (Knowles SPH0645LM4H)
• Indoor air quality (Sensirion SGP30)
• Hall effect (Texas Instruments DRV5023AJQLPG)
• Barometer and altimeter (HopeRF HP203B)
• 3-axis accelerometer, 3-axis gyroscope, 3-axis magnetometer (TDK ICM-20948)
• 3-axis accelerometer, 3-axis magnetometer (STMicroelectronics LSM303AH)
• 3-axis accelerometer (Kionix KX023-1025-FR)
• 3-axis accelerometer (Kionix KXTJ3-1057)

These are left available to leverage the same design in other applications or settings such as education.

Mainboard firmware

Refer to https://github.com/LEAT-EDGE/ambient-firmware-zephyr for the new, Zephyr RTOS-based firmware (compatible with both STM32L4 and STM32U5), and to https://github.com/LEAT-EDGE/ambient-firmware-arduino for the old Arduino-based firmware (not compatible with STM32U5).

Mainboard fabrication notes

PCB

Standard 2-layer 0.8mm stackup:

• 2 layers (front/back),
• 0.8mm thickness,
• 1oz copper,
• FR-4 dielectric,
• HASL finish.

No special requirements, any solder mask and silkscreen color.

Gerbers are provided but can be re-generated from the KiCad project.

Assembly

Recommended automated assembly for top-side only.

Manual assembly for top side:

• J20, J21, J22 and J23 pins (through-hole), to be inserted or cut flush with the back side.

Manual assembly for bottom side:

• C16 and C42 capacitors (SMD),
• J2J14 and J4 connectors (through-hole).

Acknowledgment

Original design in Altium from Manh-Thao Nguyen.

This derivative work was performed and licensed under an open-source license with permission from the original authors.

For the submission to the PCBWay 2026 KiCad PCB Design Contest, the following changes have been made:

• schematics rewritten from scratch with KiCad in a more readable way,
• PCB layout made from scratch with KiCad, routed on 2 layers (original design: 4 layers).

The following ideas from the original design are kept mostly unchanged:

• bill of materials,
• circuit layout,
• mechanical layout,
• component placement.

This enables this design to be used as a drop-in replacement of the original design, with the same enclosure, daughterboard and software.

This project has received funding from Université Côte d'Azur and CERN.