ITU‐T's Technical Reports and Specifications 257 Table 1 – Comparison of various hardware platforms for use in wireless sensor networks16 The last decade has seen an explosion in sensor technology. There are currently thousands of potential sensors ready to be attached to a wireless sensing platform. Additionally, advances in micro‐electromechanic devices (MEMS) and carbon Nano‐tubes technology are promising to create a wide array of new sensors. They range from simple light and temperature monitoring sensors to complex sensors able to monitor more parameters and work as ”digital noses” for electronic air quality control etc. 2.3.2.4 Interfaces There are two general ways to interface with sensors that can be used in sensor networks: analog and digital. Analog sensors generally provide a raw analog voltage that corresponds to the physical phenomena that they are measuring. Generally these produce a continual waveform that must be digitized and then analyzed. While seemingly straightforward to integrate, raw analog sensors often require external calibration and linearization. It is common for the sensor to have non‐linear response to stimuli. The host controller must then compensate in order to produce a reading in meaningful units. Depending on the characteristics of the sensor this can be a complex process. In many cases the translation may depend on other external factors such as temperature, pressure, or input voltage. A second difficulty in interfacing with raw analog sensors is that of scale. Each sensor will have different timing and voltage scales. The output voltage will generally contain a DC offset combined with a time‐varying signal. Depending on the ratio of signal to DC component, an array of amplifiers and filters may be required to match the output of the sensor to the range and fidelity of the ADC being used to capture it. Digital sensors have been developed to remove many of these difficulties. They internally contain a raw analog sensor, but provide a clean digital interface to it. All required compensation and linearization is performed internally. The output is a digital reading on an appropriate scale. The interface to these sensors is via one of a handful of standard chip‐to‐chip communication protocols. ____________________ 16 Extracted from http://www.isi.edu/~ johnh/PAPERS/Conner04a.pdf