Nanobaro is a simple barometric pressure and temperature sensor using Arduino Nano and the BMP180 digital pressure sensor. It outputs data via the Nano's built in USB-serial interface in NMEA0183 syntax. Works directly with OpenCPN's dashboard plugin (barograph history) or any other NMEA data consumers.
Nanobaro outputs one NMEA0183 XDR (transducer measurement) sentence with talker id WI (weather instruments) every 10 seconds. Here's an example:
$WIXDR,C,24.59,C,TEMP,P,1.02412,B,BARO*5E
This reports a temperature reading of 24.59 degree Celsius from a transducer with the id TEMP and a pressure reading of 1.02412 Bar (1024.12 millibar) from a transducer with the id BARO. The SI Pascal unit should really be used here, but was found to be unsupported by the targeted OpenCPN, so Bar was used instead.
Nanobaro will also output human readable TXT sentences at startup and if anything goes wrong.
The hardware is very simple. It's a BMP180 chip connected with four wires to a I²C clock/data pair as well as ground and 5V on the Arduino. More information and photos can be found on my related blog post.
Program nanobar.ino onto your Nano. You will need the Wire (I²C) library included with the Arduino package as well as the SFE_BMP180 library from Sparkfun.
There is no other software included. I'm using OpenCPN's dashboard plugin, with a separate dashboard containing only the Barometric history widget. You can either directly connect to the Nano's USB-serial device with OpenCPN, or via a NMEA multiplexer such as kplex, which lets you easily make the data available to multiple devices on a wireless or wired network.
- BMP280 version: https://github.com/dolabriform/nanobaro_bmp280
- BME280 version: https://github.com/roaxth/NanoBaro-bme280-Baro-Temp-Humidy-for-OpenCPN