NMEA Fuel-flow Sensor

This repository holds the software and documentation for the onboard fuel-flow instrumentation of our Touring Motor Glider D-39.

Concept

The actual sensor outputs a square wave whose frequency corresponds to fuel-flow.

We use a ESP32 to read the sensor and present the data as an NMEA-Sentence over Bluetooth LE.

The sentence is of the form $PFLO,xxx.x*??, where xxx.x is the number of ticks per second and ?? the checksum.

Our calibration factor is 8600 ticks per liter.

Setup Build Environment

• zephyr development environment setup as described in https://docs.zephyrproject.org/1.14.0/getting_started/installation_linux.html
• install esp32 specific toolchan as described in https://docs.zephyrproject.org/latest/boards/xtensa/esp32/doc/index.html

Build Application

Create a build folder and run cmake before building the application using ninja.

mkdir build && cd build
cmake -GNinja ..
ninja

Flash Application

Assuming esp32 is connected via /dev/ttyUSB0 use

ninja flash

Otherwise the esp device path has to be set during build.

Alternative Flashing

esptool.py can be used to flash the firmware. Install it by

pip install esptool

and use the following command to flash our binary

esptool.py --chip esp32 --port /dev/ttyUSB0 --baud 460800 write_flash -z 0x10000 zephyr.bin

Build and run tests

Tests are contained in the subfolder test as separate zephyr application. By default this application runs on qemu-arm-m3. Build Instructions can be found in test/README.md.