Schematic Digaram of a Sensor Node

Sensor Network is made up of many sensor nodes. These nodes are tiny in size. They have limited, power supply, memory and processing capability. Each sensor consists of, Transceiver, Power supply, Processor, Memory and Sensors. The overall architecture of a sensor node is shown in the diagram below.

Overall Architecture of a Sensor Node(click on the pic to see enlarged view)

Every sensor node should try to meet various design requirement of any sensor network, i.e. they should be inexpensive, small, less power consuming, robust, and equipped with right sensors to sense the environment. The node should be as small as 1 cc in size , weigh less than 100 g , be cheaper than 1$ and dissipate power less than 100 micro Watt.However it may not be possible in to meet all the above said requirements all cases or in many cases .

Power Supply: The power supply unit of the sensor node is responsible to provide power to all other components in the sensor node. The power supply can be rechargeable or non rechargeable in nature, the later one being most common. The supply is generally from 3 to 5 V, in most cases it is DC battery. Having a power source which generates energy by some means (Using Solar energy), so that node is provided power for a longer time is more desirable, however it will be expensive.

Micro controller: It is the CPU of the sensor node. It is responsible for all processing and decision making. Many chip makers have produced micro controller for the purpose of sensor node. Intel is one of the leaders in the production. These are some of the processor that can be used ARM7, Atmel, AVRIntel, Xscale , Intel 8051, PIC, and TI MSP430 . Micro controller will be interfaced to the transceiver and sensors.

Sensors: These are responsible to sense the surrounding environment and inform the controller about the phenomenon being observed. There are different sensors available they are Light Sensors, Pressure Sensors, Humidity Sensors, Gas Sensors, Temperature Sensors and many more. These sensors are further divided as active and passive sensors. Instead of sensors actuators also can be used. Sensors sense the physical quantity convert it to electrical signals process the same and obtain digital data and give it to the controller.

Transceiver: Transceivers are responsible to transmit and receive data to and from the communicating media. Communication media in most cases is air. Laser, Infrared and RF based Transceivers can be used according to what is used for communication. RF based communication is most preferred form, as laser and infrared require direct sight of communication. Generally transceivers work in ISM band, which is license free band. Transceivers are interfaced to micro controller using transceiver chip. The most commonly used transceivers chips are CC1000, CC1020, and CC2420.

Memory: Sensor nodes will have programmable Flash memory and RAM in most cases. The flash memory used in MSP430 is 48KB and it has 10KB RAM. So the protocols that are designed for the sensor network should be simple enough to be loaded into the available memory.

Some sensor node may also have Location Finding system such as GPS and mobilizers (which assist the sensor node to move form one place to another if the application requires it).