Sensor node

Nowadays, motes focus on providing the longest wireless range (dozens of km), the lowest energy consumption (a few uA) and the easiest development process for the user.

They are hardware devices that produce a measurable response to a change in a physical condition like temperature or pressure.

Sensors measure physical data of the parameter to be monitored and have specific characteristics such as accuracy, sensitivity etc.

The continual analog signal produced by the sensors is digitized by an analog-to-digital converter and sent to controllers for further processing.

As wireless sensor nodes are typically very small electronic devices, they can only be equipped with a limited power source of less than 0.5-2 ampere-hour and 1.2-3.7 volts.

[citation needed] Transceiver Sensor nodes often make use of ISM band, which gives free radio, spectrum allocation and global availability.

The possible choices of wireless transmission media are radio frequency (RF), optical communication (laser) and infrared.

However, since the wireless sensor node is often placed in a hard-to-reach location, changing the battery regularly can be costly and inconvenient.

An important aspect in the development of a wireless sensor node is ensuring that there is always adequate energy available to power the system.

Batteries, both rechargeable and non-rechargeable, are the main source of power supply for sensor nodes.

They are also classified according to electrochemical material used for the electrodes such as NiCd (nickel-cadmium), NiZn (nickel-zinc), NiMH (nickel-metal hydride), and lithium-ion.

Current sensors are able to renew their energy from solar sources, Radio Frequency(RF), temperature differences, or vibration.

A DVS scheme varies the power levels within the sensor node depending on the non-deterministic workload.