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PWJ Strain Logger

Overview

This is a Zephyr RTOS project that utilizes a RTOS to measure the stress/strain exhibited by a Pulse Water Jet (PWJ). It does this by reading a straingauge that goes to a wheatstone bridge then is filtered and into a STM32F767 microcrontoller. It utilizes the DMA controller to read off of the ADC and store to a microSD as fast as possible since the PWJ operates at 20 kHz or 40 kHz. The accompanying daughter board to the Nucleo STM32F767ZI is located in the repository Nanomagnetics Lab.

Requirements

You are required to have the PWJStrainLogger daughter board which includes a microSD card reader.

Installation

Please see the Zephyr Getting Started Guide to set up the build system. For brevity I will include the basic steps.

For ZephyrRTOS v2.7.0 (pwjrtos is built against this), we require cmake >= 3.20.

pip install west
west init ~/zephyr
west update
west zephyr-export
cd ~/zephyr/zephyr
git checkout v2.7.0
pip3 install -r ~/pwjrtos/zephyr/scripts/requirements

You need to setup an embedded toolchain. gcc-arm-none-eabi was used here. It can be installed via,

sudo apt install gcc-arm-none-eabi    # Debian/Ubuntu
sudo dnf install arm-none-eabi-newlib # Fedora/Redhat
sudo port install arm-none-eabi-gcc   # macOS by MacPorts

Then you need to add the following exports to your shells rc file,

export ZEPHYR_TOOLCHAIN_VARIANT=cross-compile
export CROSS_COMPILE=/usr/local/bin/arm-none-eabi- # macOS via MacPorts
export CROSS_COMPILE=/usr/bin/arm-none-eabi-       # Linux

You should be able to build the blinky example to ensure everything works.

cd ~/zephyr/zephyr
west build -p auto -b <your-board-name> samples/basic/blinky

Devicetree details

The device tree is very basic as we will only need two buttons to interface with. The ADC is designed to run manually outside of the Zephyr RTOS API because of the lack of continuous mode throught the DMA channel. As shown, the sw0 devicetree alias must point to a child node of a node

Building and Running

This sample can be built for the Nucleo STM32F767ZI in this example we will build it for the nucleo_f767zi board:

cd ~/zephyr/zephyr
git clone https://github.com/nanomagneticslab/pwjrtos.git
west build -p auto -b nucleo_f767zi pwjrtos
west flash

You can set the debugging options in prj.conf.