WeatherStation

Arduino code, tools and utilities to receive and publish data from an Oregon Scientific weather station.

The Arduino code here is a modified version of the decoder found at http://jeelabs.net/projects/cafe/wiki/Decoding_the_Oregon_Scientific_V2_protocol.

Hardware

• Arduino-compatible board.
• 433MHz receiver. I bought the Freetronics 433MHz shield, but any old 433MHz receiver will do. The data pin from the receiver should be connected to analogue pin 1 (the Freetronics shield connects the input to D8, I ran a jumper from it to A1).
• An Oregon Scientific THGN132N temperature / humidity sensor. This was the sensor provided with BAR808HG weather station.
• A Linux server. The arduino is plugged in to my Ubuntu media server, but any current distribution should be fine.

Software

The Linux server will need:

• rrdtool (rrdtool package in Debian/Ubuntu)
• python, and python rrdtool interface (python-rrdtool in Debian/Ubuntu)
• cron
• A web server. I use apache on this box.

udev is optional but nice to have.

As well as the arduino sketch, this repository contains:

• weather-station.rules. A udev config fragment to give the arduino a persistent device name. Update this file with your arduino's serial number, stick it in /etc/udev/rules.d/, and the arduino will always be available as /dev/weatherstation when it's plugged in.
• rrdtool-create.sh will create an RRD to store temperature and humidity.
• serial-test.py will poll the arduino and retrieve the latest weather data.
• weatherpoll.py polls the arduino, parses the received data, and updates the RRD.
• suntimes.sh downloads sunrise and sunset data, which is used in graphs.
• graph.sh generates graphs.
• weatherstation.cron is entries from my user crontab to run everything.

THGN132N Decoding

This sensor uses the Oregon Scientific V2 protocol. The Ook_OSv2 sketch from http://jeelabs.net/projects/cafe/wiki/Decoding_the_Oregon_Scientific_V2_protocol decodes the data packets. A data packet looks similar to Oregon Scientific devices - the header stuff is identical, and numbers from the sensor are stored in binary-coded decimal. A sample packet looks like this:

1A 2D 10 EC 32 27 50 06 44 25

The nibbles that I know about are:

• 0-3: Device ID. The ID for THGN132N sensors is 1A2D.
• 4: Channel. This corresponds to the channel slider on the back of the sensor.
• 5: Battery? All of my readings have 0 for this nibble. I'm half-expecting it to become non-zero on low battery.
• 6-7: Rolling code. This is a unique identifier for the sensor. It resets when the battery is replaced.
• 8: The tenths digit of the temperature.
• 10: The tens digit of the temperature.
• 11: The unit digit of the temperature.
• 12: The unit digit of the humidity.
• 13: The sign for the temperature. This nibble will be 0 for a +ve temp, and non-zero for -ve. During my testing with the sensor in the freezer, I've only seen this return 0 or 8.
• 15: The tens digit of the humidity.

The sample packet above is from a THGN132N on channel 1 with rolling code EC. It's returning a temperature of +27.3°C, and humidity 65%.

I'm expecting the checksum to work like other Oregon Scientific devices, but haven't yet implemented it.