pmc-opcua

Zephyr RTOS application for Arduino Portenta Machine Control that reads an AM2302 sensor and exposes the latest values through an open62541-based OPC UA server.

What it does

• Samples an AM2302 (DHT22) every 5 seconds.
• Publishes the latest temperature, humidity, and sensor-health values as OPC UA variables.
• Serves OPC UA over Ethernet on a fixed IPv4 address.
• Keeps local USB CDC logging active even if Ethernet or OPC UA startup fails.

Current validated runtime endpoint:

• Board IP: 192.168.1.50/24
• OPC UA endpoint: opc.tcp://192.168.1.50:4840

Current exported node IDs:

• ns=1;s=pmc.am2302.temperature_c
• ns=1;s=pmc.am2302.humidity_rh
• ns=1;s=pmc.am2302.sensor_ok

Hardware

• Board: Arduino Portenta Machine Control
• MCU target: arduino_portenta_h7/stm32h747xx/m7
• Sensor: ASAIR AM2302 / DHT22
• Network: Ethernet

AM2302 wiring used by this app:

AM2302 pin	PMC pin	Notes
+	3V3	Power
out	I2C SDA (PH8)	Used as GPIO, not as I2C
-	GND	Ground

The devicetree overlay disables i2c3 because the Grove SDA pin is repurposed as the DHT data line.

Workspace Model

This repository is the app/ manifest repository inside a west workspace. The intended layout is:

pmc-opcua/                  <- west workspace root
+-- app/                    <- this Git repository
+-- build/                  <- west build directory (generated)
+-- zephyr/                 <- west-managed Zephyr tree
+-- modules/                <- west-managed modules, including open62541
+-- tools/                  <- west-managed tools

Important implications:

• Git root is app/, not the workspace root.
• Build and flash commands are run from the workspace root.
• open62541 is fetched as a separate west project into modules/lib/open62541.
• The app points Zephyr at the module through EXTRA_ZEPHYR_MODULES=../modules/lib/open62541/arch.

Prerequisites

• Python 3 with venv
• Git
• A Zephyr SDK installation with the arm-zephyr-eabi toolchain
• dfu-util for flashing

Validated versions in the current project state:

• Zephyr: v4.3.0
• open62541: v1.5.0
• west: v1.5.0
• Zephyr SDK: 0.17.4

Setup

Create a west workspace and clone this repository into app/:

mkdir pmc-opcua
cd pmc-opcua
git clone https://github.com/dongmin-dev/pmc-opcua app
python3 -m venv app/.venv
app/.venv/bin/pip install --upgrade pip west
app/.venv/bin/west init -l app
app/.venv/bin/west update --narrow -o=--depth=1
app/.venv/bin/west zephyr-export
app/.venv/bin/west packages pip --install

Make sure the Zephyr SDK is installed and visible to the build environment, for example:

export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
export ZEPHYR_SDK_INSTALL_DIR=$HOME/zephyr-sdk-0.17.4

Install dfu-util with your platform package manager. On macOS:

brew install dfu-util

Build

Run builds from the workspace root:

cd /path/to/pmc-opcua
app/.venv/bin/west build -p -b arduino_portenta_h7/stm32h747xx/m7 app

Flash

This board does not reliably enter DFU mode automatically from west flash. Before flashing, manually press the reset button twice to enter DFU mode.

Then flash from the workspace root:

cd /path/to/pmc-opcua
app/.venv/bin/west flash -d build

Runtime Verification

USB CDC logs are exposed through the board console. On macOS the device usually appears as /dev/cu.usbmodem*.

Example:

screen /dev/cu.usbmodem101 115200

Expected runtime behavior:

• A shell-backed USB CDC prompt appears as uart:~$.
• The board logs AM2302 samples roughly every 5 seconds.
• The OPC UA server listens on port 4840.

Example log line:

[00:00:36.820,000] <inf> pmc_opcua: AM2302 temperature_c=24.90 humidity_rh=53.00

To verify network reachability from the host:

ping -c 3 192.168.1.50
nc -vz 192.168.1.50 4840

Any OPC UA client can read the exported nodes. The project has been exercised with Python asyncua and standard desktop OPC UA clients such as UaExpert.

Project Notes

• CONFIG_OPEN62541_NAMESPACE_ZERO="REDUCED" is required so the application variables can be added under the standard Objects folder.
• open62541 allocations are routed to SDRAM to preserve SRAM headroom during USB and network bring-up.
• The Portenta flash layout is expanded in the board overlay by deleting slot1_partition and growing slot0_partition.
• CONFIG_PHY_INIT_PRIORITY=76, a PHY power-up delay, and no-reset in the overlay are currently required for reliable Ethernet bring-up on this board.
• The repository carries an open62541 Zephyr compatibility patch at patches/open62541-v1.5.0-zephyr-zsock-fd-set.patch.

Troubleshooting

west flash cannot find the board

• Put the board into DFU mode first with a double reset press.
• Re-run app/.venv/bin/west flash -d build after the board re-enumerates.

The host cannot reach 192.168.1.50

• Check that the Ethernet cable is connected directly to the PMC.
• Put the host on the same subnet, for example 192.168.1.x/24.
• Confirm the app booted cleanly over USB CDC before debugging the network path.

OPC UA nodes stay at 0.0 or false

• Check AM2302 wiring.
• Confirm the sensor data line is on PMC Grove SDA (PH8).
• Watch USB CDC logs for AM2302 read failed.