Thursday, 25 October 2012

Remote weather station using Raspberry Pi and Arduino

To make the weather station actually useful, the sensors need to go outside. Running a cable to the Raspberry Pi wasn't a good option, so I dug out a pair of XRF serial radio modules to handle sending the weather data over wireless.

An ATMEGA328 chip is used to run Arduino code that pulls raw data from the sensors and pushes the processed weather data over the serial radio link.

Outdoors module for the weather station

The ATMEGA chip sits on a custom board (actually its an Arduino shield prototyping board) that includes a power regulator for the 3V3 rail (for the XRF and sensors) and breaks out headers for the XRF module and sensors. At the moment its connected up with jumper cables, but the intent is to remote the sensors in a box that can have free air movement, whilst the processor, radio and battery sit in a snug, dry box.

The weather data comes from a BMP085 temperature and pressure sensor, a humidity sensor and a light-dependent resistor. More sensors (rain gauge, wind speed and direction) can be added with some code mods.

At the moment the system is mains powered; there is a battery holder for 1xAA rechargeable. The intent was to use a solar source to top up the battery and to use a buck booster to raise the 1.2V battery output to 5V for the ATMEGA chip. Battery life without solar top-up is around 5 hours... not good for the UK in winter! I'm using a low-power mode that only fires up the ATMEGA chip every 8 seconds (using the watchdog timer function) - the system waits 5 minutes between transmitting data. This is an attempt to eek out the power, but I think the honking 3V3 regulator and always-on-XRF are sapping the battery juice. I intend to play with a LiPo battery to see if we can get better performance... the original design intent allowed an output pin from the ATMEGA to drive the XRF such that it could be powered up only when needed to send data over the wireless.

Code to follow...

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