Monday, March 21, 2011

MSB430 Sensor Mote

When we are working on wireless sensor networks we find different hardware platforms developed by different vendors. Even though in each sensor mote hardware we find lot of differences, there are basic components or modules that exist in each and every wireless sensor node. Any mote requires a processing unit which is the central brain of the mote. Usually thay use microcontrollers(MCU) for this purpose rather than ordinary PC microprocessors becase MCUs operate with very little energy consumptions. Most of the MCUs we have out there in the market are targetted for environments where we have to rely on batteries.
    Usually these MCUs carry internal memory modules that can store program instructions and data within the MCU. But depending on the requirements of the sensor network developers, extra storage space may be necessary. Therefore usually a sensor mote contains a way to extend it's memory capacity by integrating with external units. These memory units can be EEPROMs or SD-/MM cards.The next important thing on a wirelless mote is the communication module. A mote should be capable of transmitting and receiving signals from other similar motes and devices in the sensor network. The transmission medium can be redio frequency, optical communication or infrared. The most common way of communicating between motes is radio frequencies since thay are very reliable. Unlike optical and infrared signals, the radio signals don't get interfered by environmental events and energy sources.
    At last sensor motes contains different sensors to gather data which is their ultimate task. The ability to plugin additional sensors is an added advantage in sensor motes rather than just using what the manufacturer of mote has shiped it with. Usually sensors are available to sense temparature, humidity, acceleration, vibrations, light, and so on.
    Now if we talk about our main topic the MSB430 sensor mote, it's a one which is specifically designed to use on research and academic purposes rather than industrial usages. MSB430 is a product of ScatterWeb which is a German vendor. It has an MCU called MSP430 developed by Texas Instruments, USA. This MCU offers 60KB of memory divided into 5KB of RAM and 55KB of flash-ROM. In addition to that it contains a SD-/MM card slot which supports upto 4GB storage.
    The radio transceiver of the sensor mote is a Chipcon CC1020 transceiver which operates on ISM band and has the ability to select the communication frequencies by software. Therefore selecting multiple channels for advanced routing schemes is supported with this tranceiver. For analog data in and out, the mote contains 2 A to D converters. To program the wireless mote we can use JTAG inerface. In addition to that we can connect the mote to a PC by the USB port with the help of a FTDI converter cable. When we connect it to the PC with USB port, we can put the mote to the USB mode by using it's switch on the main board. At this mode, it doesn't require the usual power supply with 3 AAA batteries since it can get the power though USB cable from the PC.
    When we are going to program the mote for our purposes we have differet software options. The hard way is programming it from scratch. If we're looking for some easier way, we have operating systems that can be installed on the mote. If so, we have to just write applications on top of the operating system. The manufacturer of the mote ScatterWeb itself provide an operating system called ScatterWeb operating system. And the Contiki operating system is also ported to MSB430 platform. If we're going to develope applications on Linux PCs for the Contiki operating system to run on MSB430 motes, we need some development tools installed in our Linux machine.
    GNU community provides compiler tool chains for the GCC compiler to support development for Contiki on MSB430. To install the tools and libraries we have to first add the below software source to the /etc/apt/sources.list file. 
    deb i686/
Then run these commands on the shell.
    apt-get update
    apt-get install binutils-msp430 gcc-msp430 msp430-libc msp430-jtag
Now our development environment is ready. So, it's time to write some apps, install and run on our MSB430 motes.

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