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Matthias Wagler

03.04.2012

Making things talk: Open thoughts on connecting low cost electronics

Ever wanted to connect low cost devices in realtime wirelessly to the Internet or simply building a sensor network? We too! This is why we started a little research initiative on possible solutions and their dis/advantages. Since this aim seems to be like a big piece of cake, we decided to slice it into smaller bits and bytes – so the first thing we wanted to get familiar with was connectivity.

As a starting point, the Arduino world is still a good platform to have a fast and cheap setup including the variety of technologies out there.

Therefore we took a closer look on well known radio-modules like XBee and RFM12B, Bluetooth modems, the Ethernet shield and lastly Sparkfun’s WiFly shield.

Our insights and findings

Since Ethernet is bound to cables and the WiFly shield library couldn’t convince with stability, we decided to stop following these paths. Another reasons for killing especially the Wifi solution was pricing (around $90) and its high power consumption (even though the new WiFly version has a sleep-mode function). For sure there are cheaper modules out there, but still the fact that every sensor needs to obtain an IP address was quite scary – especially if you think about the low powered ATmega-fact.

Bluetooth is easy to implement and its range can go up to 100 meters on class 1 standard, but the modules are still a bit too expensive – around $40.

We stick to radio with two options left: the XBee and RFM12B. XBee is quite well known and provides a wide range of different modules and antenna options. On the other side the RFM12B offers a similar functionality including a lower price ($7).

The winner is…

Finally, the perfect match is called JeeNode by JeeLabs – a low cost combination of RFM12B and a microcontroller. Moreover the JeeNode is relatively cheap (18,50 Euros) and provides a very nice library for the RFM12B module. Since the JeeNode uses the ATmega328p, you can easily upload your Arduino sketch to it. Note that there is a demo sketch that enables communication with fs20-devices for home automation.

In terms of power consumption the JeeNode Micro archived some very astonishing results with 75 days uptime just powered by a little coin cell battery.

Assembled JeeNode v6

Ongoing thoughts and next steps

The connection between two JeeNodes worked out smoothly. But still the modules are not connected to the internet nor a proper sensor network is established. Anyways, we are looking forward to mix some promising approaches like websockets and node.js to come up with a nice solution to send and receive data from low cost and low powered devices.

Things are looking very good so far – so stay tuned, we’ll keep you updated!