I’ve decided to wire my office with a small wireless sensor network to learn more about hardware electronics. I’m aiming to set up 2 or 3 small temperature and light sensors and have them wirelessly beam their readings to a central collection point. Apparently there are a ton of other people who are doing this sort of thing — so many that there is an O’Reilly book dedicated to the subject. (A book which I ought to read but in typical fashion I decided to dive in on my own.)
After hacking around with an Arduino kit and buying some sensors, I’m ready to move into the integration phase of my project. For a long time I had been stymied by not being sure what radio technology to use, and so the next week or so is dedicated to evaluation. I found this really great summary of the current “state of the art” by Stuart Poulton. I have dug around on this topic quite a bit making lists of different boards and prices, and I think his review is really spot on. However, my needs go beyond just a transmitter/receiver. I am really looking for an Arduino-based platform that integrates both the RF module and an AVR microprocessor into one neat package. So what is low cost, easy to acquire, Arduino compatible and easy to integrate?
After much research, I’ve narrowed this down to the Ciseco XRF and the AVR + RFM12 boards. The XRF is based on a TI chipset and Ciseco also makes an integrated chip they call the RF Micro or RFu. I have 3 of these on order, but frankly I’m already a little worried because of the hassle factor — they (apparently) lack standard 0.1″ breadboard spaced pins, require overseas shipment to Cambridge, USA, and don’t have an onboard power regulator. On the upside, the protocol is very simple — its basically just a serial port shared among a set of devices so theoretically a really easy-to-program platform. Ciseco’s XRF takes care of error checking, retransmission, packetizing, etc.
The HopeRF RFM12 initially scared me off due to its complexity. First of all, it looked complicated to use and puts the protocol burden on the microprocessor. Two vendors have integrated AVR/Arduino and RFM modules: Jeelabs and LowPowerLabs. JC, the guy behind Jeelabs really has contributed a lot of great libraries and insights on making low power sensors. I was very temped to buy one of his Arduino + RFM packages, but he has commited to a form factor that makes use of pluggable modules that don’t suit my style of electronics hacking. LowPowerLab, run by Felix Rusu seems to have come up with the answer: The Moteino. Its basically a full Arduino Uno in a postage-stamp sized package. Felix also has some great examples and code libraries, designed the unit for solderless breadboard 0.1″ pitch and included a power regulator to boot. I put in an order for 3 Moteinos.
So now the race is on: Moteino or XRF?
Will update more later.