In addition to giving them a range of choices for connecting their sensor systems, the alternatives present developers with some tough multiple choice questions they will have to answer about their designs including:

Do I want wired or wireless? What are the choices and what are the tradeoffs? Where do I put the network intelligence, centrally or in the periphery in the devices? Do I use 8- or 16-bit devices? RISC or digital signal controllers? And once put into the field, how to I maintain upgrade and even perform debug operations on them without going off-line?

Tough enough for wired networks. But for wireless control networks - even though Zigbee Consortium has done a good job in promoting its protocol - there are a number of better suited protocols that will work with the IEEE 802.15.4 spec. This means developers will be faced with even more multiple choice questions.

Wired USB vs Ethernet
In "Working with USB/Ethernet Software for Distributed Sensor Networks (ESC-223)," Eric Gregori makes it clear that even though wireless connectivity is gaining most of the headlines, there are a a number of cost effective choices available if an embedded designer wants to go with a wired solution. Among the choices, he says, are number of embedded TCP/IP Ethernet alternatives as well as the use of the Universal Serial Bus (USB), a protocol traditionally associated with linking peripheral devices to the desktop computer.

"Connectivity options associated with computing, such as Ethernet and USB, are enabling network innovations for home/industrial automation," Gregori says. "The low cost of Ethernet-enabled silicon and embedded TCP/IP has opened the door for small distributed Ethernet-based sensor/control networks." In addition, he says, the low cost of USB enabled silicon and embedded USB stacks, has opened the door for small distributed USB based sensor/control networks.

Both USB and Ethernet have advantages when designing distributed sensor / control networks," says Gregori. "The primary advantage for USB is power distribution and network cost. Power distribution is built into the USB specification, 100ma per device, or 500ma per device for powered hubs (with software negotiation). The power distribution system is built into the cabling, hubs, and hosts. Another advantage is low cost USB devices. A variety of low cost USB devices designed to be connected to a PC can be used in the sensor network."

The advantages of Ethernet, he says, are performance and compatibility. Ethernet and TCP/IP enabled sensors do not require a gateway to connect to a PC LAN network. This makes the sensor data significantly easier to get to the internet for remote monitoring around the world. WiFi compatibility is also an advantage if the sensor network is within range of a existing WiFi network.

"When designing a sensor / control network for a device that will have a local controller ( for instance a manufacturing machine ) a USB network is a good option," says Gregori. "Assuming the sensors draw less then 100ma, the USB wiring can be used as the power distribution network, eliminating the additional cost of power wiring.

But he points out that when designing a sensor/control network for a device that will be remotely monitored or controlled, an Ethernet network is a good option. "In most cases, the PC LAN network in the building can be used as a connection to either a remote node in the same facility, or a remote node on the internet."

Wireless connectvity's multiple choices
For a connectivity protocol that was still in an embryonic state in the late 90s, the potential of the IEEE 802.15.4 wireless spec in embedded systems designs has increased dramatically.

According to Matt Maupin, who will be presenting "IEEE 802.15.4: Providing the foundation of wireless sensing and control (ESC-343)," while everyone is looking for the nirvana of a single technology to solve all the market needs, this rarely happens. Wireless sensing is no exception." However, he said, with 802.15.4, it is possible to have a common base to provide a superset of technologies to cover the majority of sensing and control applications.

In addition, to Zigbee, he said, developers now have a choice of wireless control alternatives, including the Freescale Synkro networking protocol, WirelessHart, and the SP100/ISA100.11a network stack, all of which he will cover in detail in his class.

But which one is best?

"The answer, of course, is it depends on the application," says Maupin. "The two key factors to look at are cost and the target market (consumer, commercial and industrial) as these factors tend to be at opposite ends. For example, if a solution is built for the industrial needs, the cost tends to go up. At the same time, to keep the consumer device cost down, features and flexibility are often stripped out.

Synkro technology, he says, targets consumer devices and has been developed with cost in mind. From a silicon standpoint, the ICs can be simplified to remove much of the I/O while memory is the least required of all stacks discussed. This allows smaller ICs with less memory to be developed to address this specific market.

ZigBee technology is the next market up, and in general has the largest market appeal. "However, it fits best in the commercial space, " says Maupin, "but does not fit as well into the low end consumer due to cost, and is generally not perceived as an industrial fit due to lack of features such as channel hopping."

ISA100.11a and WirelessHART technology are both targeted toward the industrial market, but the mandatory 10ms time slot and 10dBm power output for WirelessHART specification will slightly increase the cost over ISA SP100.11a technology.

In both cases, he says, another cost is likely to be the stack itself. While ZigBee and Synkro networking protocol are developed by the IC makers and usually provided at no cost, it is likely that SP100.11a and WirelessHART specification will have additional cost associated with them for the stack, adding to the overall product cost.

"While there is still no 'One Size Fits All'," says Maupin, "the various protocols still benefit from many of the key technical and market advantages of 802.15.4, such as lower cost, increased vendor selection, and competitive enhancements"

How much intelligence, and where?
In "Intelligent Sensor Signal Processing (ESC-523)," Priyabrada Sinha, will discuss the fundamental problem facing developers of embedded sensor networks: where to you do you put the intelligence needed to process the data received and to make decisions on what actions to take?

"As sensor-based applications rapidly increase in complexity, it becomes imperative to embed a greater degree of intelligence to the sensor interface," says Sinha. "Many applications utilize multiple sensors to obtain a variety of measurements and process them in highly innovative ways. In some cases, the signals from multiple types of sensors must be processed simultaneously (and therefore by the same MCU), a scenario that can be termed "sensor fusion."

Each type of sensor has its own signal characteristics and requires a different set of post-processing to extract useful information from it, which increases the amount of CPU computations and peripheral data handling.

Also, in many applications, says Sinha, sensors are physically dispersed over a wide area, such as in a large building or factory, or in various parts of an automobile. A centralized processing/control approach often proves ineffective, or inefficient at best, for such distributed systems.

"To offload some of the processing and data-storage requirements from the central control unit, it is beneficial to spread the processing capability over multiple MCUs located close to, or even integrated with, the sensors," he says. "This 'distributed sensor processing' approach requires a variety of powerful signal-conversion and communication peripherals."

More connectivity options
Other useful ESC classes on embedded wired and wireless networking and sensor design include:

1) "Embedding TCP/IP (ESC-103)," "USB for embedded systems (ESC-220)," and "IP version 6 Overview and Transition Mechanisms (ESC-240/260),"  taught by Christian Legare.

2) "CAN " A secure high speed data communications bus (ESC-302)," presented by Carl Stenquist.

3) "Building and operating robust and reliable Zigbee networks (ESC-322)," taught by Zachary Smith.

4) "Security in a wireless embedded world (ESC-341)," which will be presented by Timothy Stapko and Owen Magee.

5) "RFID as a networking technology (ESC-363)," which will be taught by Martin Payne.

6) "Choosing a wireless protocol: 802.15.4 vs Zigbee vs. proprietary (ESC-403)," to be taught by Miguel Morales and Kevin Belnap.

7) "Wireless sensor network system engineer's rules of thumb (ESC-423 )," to be presented by Ilya Bagrak.

8) "What a Mesh! The Ins and Outs of Mesh Networking Technologies (ESC-443)," taught by Joel Young

To attend these and other informative classes, sign up now on the ESC registration page.