Step 1 — Choose your options: Battery back up and Power Supply.

An optional battery back-up board is shown here with the battery itself wrapped in blue tape. This one is the UPiS and is made for the older models of Raspberry Pi by pimodules – but they have just announced a version designed for the new B+ and A+ models. It looks better and is also cheaper!

You can use a micro-usb plug-top power supply – but if you do, make sure it’s a good one, rated to at least 2A (the Pi won’t use this much, but it is good to overspecify here). Watch out for cheap fakes!

We recommend using an industrial grade power supply because it gives rock solid power and long-term reliability. You will usually need to make a cable to go into the Pi. To make a micro-usb connection I suggest cutting a pre-made cable rather than trying to attach a micro usb connector yourself – the connectors are very fiddly!

Step 2 — Choose your box

Lots of choices here, I really like to have the electronics visible through a transparent lid, but you can save a few pennies if you don’t want to gaze at the electronics for some reason. About the smallest sized box for a basestation is 139x78x80mm – this means I can just squeeze the power supply below the pi.

Larger sized boxes make it a bit easier to attach cables and so on. A neat feature of the Hylec box we’ve used is that you can attach a cable gland neatly as the threaded hole is already in place.

For tight fits we found these little USB swivel adaptors useful – using these you can ‘fold’ a larger wifi or 3G dongle back over the top of the Raspberry Pi itself.

Step 3 — Radio Module and optional wifi

We use the RFM12B radio modules both in the basestation and in the sensors. I found some breakout boards on ebay but you can also get them from tindy and other places.
The radio modules come in different frequencies – 434MHz is global, whereas 868MHz is for Europe and 915MHz is for America. If you want to use them elsewhere check out your local regulations.
When buying a wifi dongle it’s worth getting one with a chipset that the Pi plays nicely with. Check out the comprehensive list over at elinux for guidance here.

Step 4 — 3G dongle option and putting it all together

If you want to provide backup connectivity and/or directly send of text message alerts you can use a 3G dongle. I just looked for well supported models on elinux and then bought one second hand on ebay.
Now secure the power supply in the box, mount the Pi on some 35mm M2.5 standoffs, and you’re good to go!
But what piece of modern hardware would be complete without some software? You’ll need to have either an SD card for the Pi models A or B, or a micro SD card for the newer models A+ or B+. 4GB is enough but again, be careful of buying the cheapest ones you can – better to spend a little extra and try to avoid fakes.