Sunday, May 16, 2010

Breakout boards - first test

Yesterday my wife went binge drinking (bachelorette party) so I finally had some time to assemble my Meshnetics breakout boards. They contain only five elements each, but assembling them is a real PITA because of the Meshnetics modules. I soldered them with normal soldering iron and used solder wick to remove any jumpers. Afer soldering I tested the boards with a multimeter set to beep. For the power supply I used two AA NiMH batteries in nice battery holder with a switch (sadly it has no place for screws). I measured the output voltage of the battery packs - it was around 2.6V for each. Meshnetics need between 1.8V and 3.6V to work properly. After assembling I connected the modules to the AVR Dragon JTAG programmer, and tried to read their signatures using AVR Studio. It worked perfectly - photo:

Breakout boards can be programmed and tested without any additional hardware, so they can be used as a very primitive WSN nodes. I didn't include any sensors and actuators on them - even LEDs or microswitches - so using them in such way would be really painful. However for a single module I can use AVR Dragon for fake I/O so it should be possible to run some software tests without designing and building target boards.

In the meantime I've also been thinking about some name for my devices. In my opinion name is a very important thing - human brain needs names to process data, and a bad name might be harmful to entire project. I'm not a native English speaker so inventing a good name is not so easy. At first I thought about "smartlets" - like smart droplets :). However it has already been taken up by Apple - from a totally different angle - smart outlets. I need to think a bit more.

Now the coffee for my wife...

Friday, May 7, 2010

WSN-intro and Meshnetics breakout boards

A couple of years ago, first news about Wireless Sensor Networks started to appear on the Web. At the beginning there were scattered pieces of information, but slowly it became a recognizable and popular research direction. I really like the idea of wireless sensor networks - tiny, simple devices called "motes" with limited sensing abilities, and processing power are used to collect data about physical and social phenomenons. Single mote has very little usefulness, but a network of them can support really innovative projects. It really sparks up imagination.

The most popular standard in the WSN area nowadays is the Zigbee. It is supported by Zigbee Alliance - association of many international companies (among them Cisco, Atmel, TI and many other). However there are many other standards around - both open and proprietary. I recently became interested in 6LoWPAN - it's a collection of standards maintained by IETF - an international non-profit organization, that also maintains IP, and other Internet-related standards. 6LoWPAN makes it possible to use IP (only v6) on low-power radio links used in WSN.

After doing some research I determined that probably the easiest way to start doing some 6LoWPAN research is to use Contiki OS - operating system for embedded devices from SICS. Contiki already supports many 6LoWPAN concepts and many other are being actively developed. Contiki is available for many different platforms, but I think that MSP430-based devices are best supported. Contiki is equipped with java-based network simulator Cooja - so it's possible to start doing research without actually having any motes. I am getting ready to test that approach - I already installed Ubuntu Linux, and I hope to start some tests soon.

Regardless of the simulator I plan to do some test with real motes. For my development platform I chose Atmel/Meshnetics Zigbit ATZB-24-A2 modules. They are quite cheap, available in Poland and contain a microcontroller, a transceiver and an on-chip antenna. I found a very good French site which contains many useful comments about these modules. My first step was to design a breakout board for the Zigbit modules. Zigbits are quite difficult to solder without hot-air station. I don't have such a station, so I plan to solder the modules once and for good to these breakout boards, and connect the boards to other devices with simple pin headers. My breakout boards will also contain JTAG and power-supply connectors - so I should be able to do some simple programming and debugging only with breakout boards. Here is the picture of the finished board next to a Zigbit module:

I made some rookie mistakes with the design - I got the description printed over the pads, but in general it looks just like I wanted :) . Now I'll have to come up with an idea how to solder it right. Any suggestions?