## Sensor Bus Standards
### Sensor Network Architectures  
Sensor network applications vary widely, ranging from several sensors within a hand-held instrument to hundreds of sensors distributed over a manufacturing facility. These networks may be hardwired, wireless, or some combination of both, according to application demands and cost considerations. Other features such as data bandwidth, power limitations, physical size, and the amount of sensor signal processing required play a significant role in establishing the architectural requirements of a sensor network. Although it is not feasible to define a standard architecture which is simultaneously optimized for all sensor applications, it is useful to review typical architectures and discuss the criteria for choosing an appropriate sensor network [9]. Sensors are increasingly being added to electronic systems to improve performance, increase lifetime, or reduce cost. When multiple sensors are utilized, the system designer must consider how to connect the sensors. When a limited number of sensors are needed, a common architecture is to use point-to-point wiring to connect the sensors to the main control system where the data will be collected. The main controller could be a PC or other control module within a system. This architecture, which is shown in Figure 5a, requires a minimum design effort where sensors can be integrated into a system with little hardware overhead, primarily using software. Although the main controllers could be networked to share information, this architecture is best for applications where sensor networking is not a primary demand. Due to the point-to-point architecture, sensor modules in this approach can be unsophisticated, \"dumb\" devices with no required signal processing or networking within the sensor itself. An alternative architecture which has become quite popular in many applications it to employ \"smart sensors\" which can be connected on a network (typically hardwired) to a master (host) control system, as shown in Figure 5b. In this approach, each sensor module contains a sensor, signal processing hardware (typically a microcontroller), and a network interface which may or may not be physically integrated with the microcontroller. The advantage of this architecture is that significant signal processing can take place within the sensor module and, by using a standard network bus, sensors can share information. The I\({}^{2}\)C bus is well suited for this architecture, and the TII (IEEE P1451.2) bus can be used when only one sensor module will be connected to the host system. This structure also lends itself well to wireless network applications. A primary disadvantage of this architecture is its limited optimization of resources; typically each sensor module operates as an autonomous unit with no sharing of signal processing and interface hardware even if sensors are located physically together. As a result, it is difficult to optimize the power dissipation or minimize the size of the overall sensor network. The final sensor system architecture that will be presented involves a much more complex, multi-layered network as shown in Figure 6. This approach utilizes a series of communication busses to transport sensor/actuator data through a sequence of increasingly sophisticated electronics. Here, sensors and actuators are connected directly to signal conditioning circuitry within a sensor node. Individual sensor nodes communicate with a microsystem controller, typically via a hardwired \"intramodule\" bus, which can perform some signal processing and correlation/fusion of data from the sensor nodes. The microsystem nodes communicate via a system bus, which may be hardwired or wireless depending on application, to share data or report to a host system for further processing and/or  
Figure 5: Sensor networking architectures a) point-to-point connections and b) networked single-sensor modules. long-term storage. Finally, the host system may be connected to a large-scale network, such as the internet.