by October 1, 2005 0 comments

The word ‘Mote’ literally means a ‘speck’ or a very small particle. In the field of computers, or embedded technology to be specific, the term refers to a class of very small-scale computers capable of collecting information from their 
environment and transmitting them over small distances. 

Intel defines motes as “tiny, self-contained, battery-powered computers with
radio links, which enable them to communicate and exchange data with one another, and to self-organize into ad hoc networks”.

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Applies to: Embedded developers
Small size, low power requirements
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To serve this purpose a mote consists of three basic components. The first is a low-cost, low-power microprocessor. This processor monitors one or more sensors, which comprise the second component. The third component is the mote’s connection to the outside world in the form of a radio link. All of these components are packed into the tiniest of packages possible. A mote derives its power from an internal battery or from an external source like sunlight or ‘vibrations’, depending upon the environment the mote is expected to operate in.

One of the earliest mote variants was the RF mote that used an Atmel processor, had 5 onboard sensors and was powered by a 3V lithium coin cell battery. It had a communication range of 5 m—30 m reaching speeds of up to 5 Kbps. The weC mote was an improvement over the Mini mote, which in turn was similar to the RF mote, and was perhaps the first mote to use the TinyOS-an OS that has become an integral part of almost all variants of motes.

TinyOS is ‘an open-source OS designed for wireless embedded sensor networks.’ It features a component-based architecture, which provides the developers enough flexibility, while ensuring a small footprint that is essential given the constraints most embedded applications work in. What this means is that developers can choose what components of the OS are needed for their application and keep out the ones not required.

The Intel mote runs on TinyOS for the OS and adds another layer for Bluetooth communication

The components of TinyOS include network protocols, distributed services, sensor drivers and data-acquisition tools. An application can choose to use them as is or, more likely, build on these components to perform tasks specific to its requirements. It is for this reason that TinyOS has perhaps become the de facto choice for almost every major mote variant. Motes from Berkley, Crossbow and
Intel are all built on top of TinyOS.

Popular motes
The Mica range of Motes developed by Crossbow features three popular variants-the original Mica, the improved Mica2 and the Mica2Dot, which is very similar to the Mica2. The Mica features the Atmel Amega 128L processor (4 MHz) and is capable of carrying data at around 40 Kbps over distances up to 100 feet on a radio link. It derives its power from 2 AA batteries, which can last up to one year in a typical application.

The Mica2 uses the same processor and has similar battery requirements and life but is boosted by increased memory and is capable of communicating within a range of 500 feet reaching speeds of up to 38.4 Kbps. The Mica2Dot has exactly the same processor, memory and communication capabilities as the Mica2, but differs in how the sensors are connected and is powered by a 3V coin cell battery instead. ‘Spec’ measuring 2 mm2 x 2.5 mm2 in size is a fully working single chip mote developed by the University of California, Berkeley, capable of communicating over distances of 40 feet reaching speeds of up to 19.2 Kbps. 

The Intel mote develops on the Berkley one, and aims to deliver a mote with more CPU power and better radio facilities, which is more secure and less hungrier in terms of power. Like all of the other motes discussed above, the Intel mote is based on TinyOS. However, it adds another layer to the OS specifically for supporting Bluetooth, the preferred means of communication for the Intel mote, as well as platform drivers and a network layer.

All this technical know-how is fine, but what real-life applications do motes have? One use could be to facilitate the creation of large-scale network of small devices with low power requirements. These devices can be designed to communicate with each other or with a ‘traditional’ reader. For example, a mote could replace your water meter and log your usage. Fast-forward to the end of the month when the Water Board truck passes by on the street, emitting a strong magnetic field that activates the transmitter in the mote, allowing it to send your usage information. All this, while, the mote is embedded deep inside the concrete in your boundary wall. But the real power of motes is in their ability to communicate with each other. So let’s modify this scenario a little. Imagine each house in the neighborhood has one of these motes for a water meter. You should have already figured out what we are about to say. That each mote periodically communicates its usage information to an adjacent mote such that this information travels up (or down, whatever you want to term this as) the chain to the last node.

A ‘super-mote’ or a ‘traditional’ reader collects this information from the last node, eliminating the need for a truck.

Motes are already being used to study the conditions (temperature, humidity etc) inside the burrows of birds and other natural habitats. They have also found applications in measuring the temperature in and around a building, and other similar

There are three main challenges with respect to the development of motes. These are ultra low-power operation, system-level integration, and hardware reconfiguration devices. Motes need to run under power constraints that are considerably lower than (even) what we consider to be traditional ‘low-power’ devices. This demands specially designed hardware and ‘power-aware’ software development. System-level integration poses the challenge of integrating the CPU core, memory, sensors and the radio (network) components into a size and cost effective package. Hardware reconfiguration is about keeping the design flexible enough to accommodate any future advancement in the underlining hardware.

Kunal Dua

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