Introduction
Here we take you through the hardware you'll need together with the options for extending the basestation.
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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!
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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!
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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!
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Now secure the power supply in the box, mount the Pi on some 35mm M2.5 standoffs, and you're good to go!
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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.
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