Back Garden Weather in CouchDB (Part 3)

In this series I’m describing how I used a CouchDB CouchApp to display the weather data collected by a weather station in my back garden. In the first post I described CouchApps and how to get a copy of the site. In the next post we looked at how to import the data collected by PyWWS and how to render a basic page in a CouchApp. In the post we’ll extend the basic page to display real weather data.

Each document in the database is a record of the weather data at a particular point in time. As we want to display the data over a whole day we need to use a list function. list functions work similarly to the show function we saw in the previous post. Unlike show functions list functions don’t have the document passed in, they can call a getRow function which returns the next row to process. When there are no rows left it returns null.

Back Garden Weather in CouchDB (Part 2)

In my last post I described the new CouchDB-based website I have built to display the weather data collected from the weather station in my back garden. In this post I’ll describe to import the data into CouchDB and the basics of rendering a page with a CouchApp.

PyWWS writes out the raw data it collected into a series of CSV files, one per day. These are stored in two nested directory, the first being the year, the second being year-month. To collect the data I use PyWWS’s live logging mode, which consists of a process constantly running, talking to the data collector. Every five minutes it writes a new row into today’s CSV file. Another process then runs every five minutes to read the new row, and import it into the database.

Because CouchDB stores its data using an append only format you should aim to avoid unnecessary updates. The simplest way to write the import script would be to import each day’s data every five minutes. This would cause the database to balloon in size, so instead we query the database to find the last update time and import everything after than. Each update is stored as a separate document in the database, with the timestamp attribute containing the unix timestamp of the update.

Back Garden Weather in CouchDB (Part 1)

When she was younger my wife wanted to be a meteorologist. That didn’t pan out, but our recent move found us with a garden, which we’ve not had before. This gave me the opportunity to buy her a weather station. I didn’t just choose any old station though, I wanted one that did wind and rain as well as the usual temperature, pressure and humidity. And, the deciding factor, a USB interface with Linux support. Fortunately the excellent PyWWS supports a range of weather stations, including the one I brought.

I’m not going to go into how I mounted the system, or configured PyWWS. That’s all covered in the documentation. PyWWS can produce a static website, but as someone who earns his living building websites I wanted something a bit better. Continuing my experiments with CouchDB I decided to build the website as a CouchApp.

As well as allowing you to query your data with Javascript, CouchDB lets you display webpages directly out of your database. If you visit welwynweather.co.uk you’ll notice that you’re redirected to a url that contains url arguments that look a lot like those used to query a view. That’s because that’s exactly what’s going on. Things become clearer when you discover that that http://www.welwynweather.co.uk is an alias for http://db.welwynweather.co.uk/_design/weather/_rewrite/. Now you can see a more complete CouchDB URL, albeit without the database name. db.welwynweather.co.uk points to an Apache reverse proxy that routes requests through to CouchDB.

Programming Documentary

I’m a huge science and engineering documentary geek. I prefer watching documentaries over all other forms of television. It doesn’t really matter what the documentary is about, I’ll usually watch it. After getting ready for my wedding I had a bit of time before I had to walk down the aisle so I watched a documentary about pilots learning to land Marine One at the White House. There probably aren’t many people who would choose to spend that time that way.

Science documentaries have experienced a renaissance over the last few years, particularly on the BBC. The long running Horizon series has been joined by a raft of other mini-series presented by Brian Cox, Alice Roberts, Marcus Du Sutoy, Jim Al-Kalili and Michael Mosely. These cover a large part of the sciences, including Chemistry, Biology and Physics. Physics in particular is regularly on our screens. Whether it’s talking about quantum mechanics or astronomy or something else it seems that Physics has never been more popular.

As someone who writes computer programmes for a living this makes me worry that your average man on the street may end up with a better understanding of quantum mechanics than they do of the computer on their desk, or in their pocket.

Sonos Review

Recently I purchased a basic Sonos system, and after just a couple of weeks I’m already in love with it and have more music playing in my house than ever before.

For those of you who haven’t come across Sonos before, Sonos produce a multi-room wireless music system. The system consists of a number of devices that connect to each other using a proprietary mesh network. You can buy Sonos devices that contain built in speakers, or ones that connect to your own as well as a device to link your iPhone and to join your existing network to the Sonos wireless network.

I purchased a Sonos Play:3, a Wireless Dock and ZoneBridge (all three links contain an affiliate id) so that’s what I’m reviewing here.

The Sonos Play:3 is as fairly small, unassuming, single speaker block. It contains three individual speakers while it’s larger brother, the Play:5 (affiliate link) contains five. The back has a power socket and a network port. The top has a mute button, as well as a volumn up and down rocker. The other devices are similarly spartan, yet stylish, in their design with minimal on device buttons.