Meteo-Pi

Meteo-Pi is a flexible, low-cost data-centre device for Davis weather stations. It’s a great new way of linking a Davis console to a powerful but green and inexpensive Raspberry Pi computer.

Meteo-Pi is a two-part cabled adapter linking a standard Davis weather station console (VP2, Envoy or Vue) to a Raspberry Pi computer. The two parts are: a console interface that fits into the console much like a traditional logger and a Raspberry Pi input adapter in the form of a microHAT (µHAT), which means that it plugs directly on to the interface pins of the Pi. The two parts are joined by a short, Davis-compatible cable with RJ11 connectors.

Meteo-Pi’s main advantage is that it allows any weather station programs able to run on the Raspberry Pi to receive serial weather data direct from the console. This provides two key benefits:

  • It allows a choice of weather programs to run on the Pi . If you try one program but decide that it doesn’t meet your requirements then it’s simple to switch to an alternative Pi-compatible program. Or Meteo-Pi may be ideal for developing your own Pi-compatible software. Contrast this with a logger/SBC like the WiFi Logger or Meteobridge where your only option is to use the built-in software;
  • Much greater memory and computing power is available with a Pi (especially if the new high-performance Raspberyy Pi 4 is used) than an integrated logger/SBC ;

The  simplicity of the Meteo-Pi design allows it to be sold at relatively low cost. Of course you still need to buy a Pi and a few associated accessories (power supply, SD card etc) but it should still be possible to build a complete and reasonably powerful data-handling solution, including the Meteo-Pi unit itself, for around $/€/£120 (and remember that  Meteo-Pi does not need a separate logger – other than the Pi, it is fully self-contained).

Meteo-Pi also offers some other important features:

  • LED indicators on the µHAT board provide a constant visual indication of communication between the console and Pi;
  • All Raspberry Pi computers are green in the sense that they have very low power consumption. A Pi can be left running 24/7 and feeding your weather data up to the Internet while consuming no more electrical power than a small mains LED light;
  • RTC: Meteo-Pi has a battery-backed real-time clock so that accurate time can be maintained on the Pi even after a mains outage;
  • There is full electrical isolation between console and Pi so issues like ground loops leading to spurious readings cannot occur. This makes Meteo-Pi especially suitable for cabled VP2 installations. (Of course, Meteo-Pi works perfectly well with wireless stations too.)
  • Zero configuration required during set-up;
  • No USB connection is involved, so potential issues like USB dropout, USB drivers, a separate USB hub etc are not relevant;

Remember also that most recent Pi versions are available with WiFi onboard and so it’s perfectly possible to locate a miniature Pi computer close to your Davis console and have it talking to other computers on your network and to the Internet over WiFi.

Raspberry Pi options

Raspberry Pi computers come of course in a number of versions. We have tested Meteo-Pi with the Raspberry Pi 3B+, 4B and Zero W versions. In all probability it will work with other and older versions too, but these are untested as yet, The three current versions that we would recommend considering are:

  • Pi 3B+: Until recently, the standard ‘full-sized’ Pi version, but still a current version and perhaps more familiar as yet than the 4B. The 3B+ is substantially more powerful than the Zero version, giving plenty of performance margin for weather station software, though it is still low-power of course in electrical power consumption;
  • Pi 4B: The latest high-performance version of the Pi giving still more computing power. The Pi 4B also is the first Pi with USB3 compatibility making it easier to connect high-speed data storage to the Pi using an external hard drive;
  • Pi Zero W: This is the smallest version of the Pi and also the version with the lowest power consumption. There is a bit more to say about the Zero than the 3B+ or 4B: The Pi Zero has less computing power than other current versions such as the 3B+ and 4B, but nonetheless is more than powerful enough to run most weather station software without breaking sweat. The other key advantage of the Zero is its small physical size. Meteo-Pi is designed to complement the Pi Zero exactly and the combination of Meteo-Pi and Pi Zero makes a surprisingly neat and tiny solution (see image right – around 80mm long) to meet all data handling requirements for a Davis station. If you do plan to use a Pi Zero then remember that you will probably need the Pi Zero WH version, which has WiFi onboard and the 40-pin header factory-fitted – it is important to seek out this version. The WH costs a little more than the plain Zero or Zero W but saves the pain of needing to solder on the header for yourself. (NB Full-sized Pi versions like the 3 and 4 have the header fitted as standard.) Note that the Zero WH only communicates to a network via WiFi. If you prefer the stability of a cabled network connection then it’s better to choose a Pi 3 or Pi 4;

Please remember that if you plan to place your Pi in a case  – which is recommended because it gives a neater overall result – then you will need a case with sufficient spare height to accommodate the Meteo-Pi HAT. A case with a transparent top is also a good idea so that you can see the LEDs on the Meteo-Pi µHAT.

What’s involved in using a Raspberry Pi?

For those unfamiliar with the Raspberry Pi, here are a few basic background notes:

The Raspberry Pi is a tiny, inexpensive computer (the Pi Zero WH version mentioned above is just £13, though you do also need a couple of accessories like  a mains adapter, SD card and, for neatness, a simple cheap case). For its size it is surprisingly powerful and is perfectly capable of running full weather station software like CumulusMX or weewx, maintaining full weather records and uploading data to weather networks like Weather Underground and to your own website. The Pi is available in several versions as summarised above. Power consumption is also tiny and there is no problem leaving the Pi to run 24/7 without any routine attention.

A Raspberry Pi usually runs an operating system called Raspbian, which is a version of Linux. This is probably the biggest difference between the Pi and more familiar Windows computers. So yes you do need to learn a little of the basics of running Linux and this is the main hurdle that Pi users need to overcome – it is different from Windows and does require a little time and effort to make the transition to running Raspbian. If you’re seriously allergic to computers then using a Pi or Meteo-Pi may not be for you. However, with a little familiarisation, using a Pi is genuinely straightforward and, beyond a few basics which are available as step-by-step instructions, there is not too much to do by way of configuration.

In the context of Meteo-Pi, you’re not going to be using a Pi as your main computer, but rather as a dedicated weather station computer running only the weather program. So all you need is how to set up the Pi and launch your preferred weather program. From then on, you’ll be making any adjustments to the weather program itself and not to the Raspbian operating system. Linux systems such as the Pi tend to run for extended periods without any of the need for periodic updates and reboots that are needed by Windows and so the Meteo-Pi should just tick away in the background for extended periods leaving you to focus solely on the weather data.

Pi computers can be set up in two distinct ways: First, you can obviously connect a keyboard, mouse, screen etc to the Pi and use it similarly to a conventional Windows computer. But the other option is to run the Pi in what’s called a ‘headless’ configuration. This means not having anything attached to the Pi other than the console connection and a power cable (and optionally – if WiFi is not available – a network cable), and controlling the Pi and viewing the data from another computer on your network. This is surprisingly easy to do with a Pi and for many users will be the preferred configuration because the only device that needs to be nearby to the Davis console is the Meteo-Pi unit itself.