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...

Live embedded Cosm graphs

As a minor bonus to the Cosm service, I found you can create an embeddable graph for your data to stick in any website...

Behold the current air pressure in Liss, live!

:)

Software Defined Radio hacks

The radio meteor project was great but has a few hang ups that are bugging me...

1. The hand-held yupiteru radio has some issues with frequency stability that makes it difficult to work out what's a satellite and what's a glitch in the radio.
2. The radio/soundcard interface seems to be susceptible to RF interference - eg from my computer monitor! This creates noise and false alarms on the meteor counter
3. To detect meteors, my PC must be on and running the speclab software with the radio attached. This is tedious and uneconomical to run 24/7
4. The feedline from the aerial to the radio is about 15m long. This may cause line losses (ie the signal gets weaker)

So to fix these I'm planning on using a digital tv USB dongle and an arduino to create a detector-in-a-box that could run off a low-wattage wall-wart and could dump data onto a USB stick or live stream over wired or wireless network onto the internet...

Fun, eh?

The system relies on a modern miracle chip built into some brands of USB digital TV dongles. The realtek Software Defined Radio (SDR) lets you tune into a huge range of frequencies (around 70MHz to 1.7 GHz). I got a generic one from Amazon for £17. There are a few sites around that list compatible dongles.

More to come on HDSDR and how to grab the data coming off the dongle...

Raspberry Pi as a Cosm data server

Part of concept I'm working up uses a base station to act as the bridge between a suite of sensors and the internet. Cosm is a web service that manages data upload, storage and retrieval and enables sharing of data streams.

Getting data off the Pi and into Cosm is reasonably trivial, but it took me a few tries to get it working, but here's the Cosm datastream. The Pi is hooked up to a BMP085, as described previously. In the end I bought an Adafruit cobbler for the convenience of hooking up to a breadboard and popped the Pi in a crust of laser-cut clear acrylic.

Raspberry Pi

Pi Power

After getting my Pi a few weeks back I've been struggling to get it further than the stock X windows GUI, let alone doing anything interesting with it. Part of the problem is having to dig out a PSU, keyboard and mouse and sitting in front of the telly with the Pi's composite out plugged into the TV AUX (all at a time when small people were cleared from the vicinity of the TV).

So I got the latest Occidentalis distro from the fantastic Adafruit Industries who built in a few handy utils and libraries (like SSH and libs to enable access to the GPIO pins). After a few test runs from the floor in front of the TV, I hooked the Pi up to my router with an ethernet cable and powered it up. Using SSH on my Linux netbook is straightforward, but you need extra software for Windows - PuTTY works well enough (although the connection has to be reset occasionally - not sure if this is the router, Pi or PuTTY...)

Next I got hold of my BMP085 pressure/temperature sensor breakout board, which uses the I2C bus to communicate with other devices. The Pi has built in I2C support brought out on the GPIO pins (one data and one clock pin for each I2C bus). Again, Adafruit have made a library and set of example programmes for interfacing with the BMP085 (amongst other things!). Connection to the GPIO pins at the mo is through an old IDE cable and hook-up wire. The Pi has 3.3V and 5V outputs right next to each other - so be careful connecting up 3.3V devices! Eventually I will make a breakout board, or buy one...

Currently I'm attempting to use Cosm to publish this data, but the examples in Python are defeating me at the moment.

New tabs

To try and organise my projects, I'm using the blogger 'pages' view. There are new tabs with an introduction and ongoing projects (here and here)

Mantis-a-like CNC miller, build part 1

I'm going from fuzzy ideas and sketchup models to actual hardware now... After sourcing silver steel from these chaps in Wales (and most of the bolts, leadscrews, nuts and a few washers...) I grabbed a lump of MDF from Wickes and started building on Saturday...

The mutt is for appreciation of scale.