Imote2 Wireless Sensor Board (Low power 802.11 b/g) (to be used with the Xbow Imote2 Processor board)
The UCAM-WSB100 is a low power high data-rate wireless board designed in the Computer Laboratory at Cambridge University (Digital Technology Group). This board is part of the Cambridge Sensor Kit (CSK) that has been developed to support the experimental work of SESAME (http://www.sesame.ucl.ac.uk) - an UK-funded project that investigates the use of sensor systems (in particular on-body wireless sensors) with off-line and real-time processing and feedback in enhancing the performance of elite athletes. This application requires the collection of a large amount of data from high sampling rate sensors placed at key measurement points of an athlete's body. The hardware reference design is open source, available to the WSN community to tailor it to a particular application need.
- Compatible with the Imote2 processor board
- Low Power 802.11 b/g based on Marvell 88W8686 chipset (Embedded Works OEM)
- Supports ad-hoc and infrastructure modes
- Access to power control of the radio system
- 12 analog channels (12-bits resolution)
- Physical dimensions: 48mm x 36mm
- Linux driver support via libertas drivers in mainline kernel (wireless board linux howto)
Technical description of the UCAM-WSB100:
We are carrying out various tests to practically understand the power consumption of the UCAM-WSB100 system within the constraints of our on-body sensor application. The trade-off between data rate, power consumption and communication range will be further explored. In the meantime, we list some back-of-the-envelope calculations that may be used as an indication of the current draw for the Marvell 88W8686 system-on-chip. The table below makes a raw comparison between two chips with different MAC level protocols (IEEE 802.15.4 and 802.11 b/g). It is important to note that any power consumption (cost) analysis should consider the data rate (benefit). In this case we used the metric energy per bit (Ebit = Power / Bit rate) for our crude comparison. Both systems have similar power budgets while in power down modes. However, the overhead for switching from the idle to sleeping modes (power down) is likely to be different, with the 802.11 b/g exhibiting higher costs.
|Chipset||IEEE MAC||RX Pw||TX Pw||Data Rate||Energy per bit (Ebit = Power / Bit rate), TX|
|Chipcon CC2420||802.15.4||19.6mA x 1.8V ~ 35.28mW||17.04 mA x 1.8V ~ 30.67 mW||250 Kbps||TX: 122 nJ/bit|
|Marvell 88W8686||802.11b/g||174.87mA x (1.8V and 3V) ~ 320.61 mW||257.05 mA x (1.8V and 3.0V) ~ 593.55 mW||11 Mbps||TX: 53 nJ/bit|
Open source hardware - Help sought
As part of our effort to develop an open source hardware platform for use in conjunction with Xbow's Imote2, we will make the details of the hardware reference design (schematics, board layout diagrams) available to the WSN community (license to be confirmed but it's likely to be GPL). Users will be able to easily tailor the system to their particular application.
We currently seek volunteers to:
- help us improve our hardware reference design
- add support for this sensor board in other operating systems (TinyOS and .Net).
If you want to get involved, drop a line to firstname.lastname@example.org
At the moment we're requesting expressions of interest to estimate a number of potential users, so we can look at options for producing a first batch of boards (to be made available at manufacturing cost).
If you're interested to get some boards for your project/application, drop a line to email@example.com
Datasheets of components on this board
All design related documentation is available under the slightly modified MIT license (added term hardware design to what is covered as Software) Available in the SourceForge files download system under CSK or follow this link CSK-WSB100 Board files download
Thanks to Brian Jones at the Computer Lab for his hardware tips, and maintaining our hardware lab up to date!