San Jose, Ca. – At the
In addition to giving them a range of choices for connectingtheir sensor systems, the alternatives present developers with sometough multiple choice questions they will have to answer about theirdesigns including:
Do I want wired or wireless? Whatare the choices and what are thetradeoffs? Where do I put the network intelligence, centrally or in theperiphery in the devices? Do I use 8- or 16-bit devices? RISC ordigital signal controllers? And once put into the field, how to Imaintain upgrade and even perform debug operations on them withoutgoing off-line?
Tough enough for wired networks. But for wireless control networks -even though Zigbee Consortiumhasdone a good job in promotingits protocol – there are a number of better suited protocols that willwork with the IEEE 802.15.4 spec.This means developers will be faced with even more multiplechoice questions.
Wired USB vs Ethernet
“Connectivity options associated with computing, such as Ethernetand USB, are enabling network innovations for home/industrialautomation,” Gregori says. “The low cost of Ethernet-enabled siliconand embedded TCP/IP has opened the door for small distributedEthernet-based sensor/control networks.” In addition, he says, the lowcost of USB enabled silicon and embedded USB stacks, has opened thedoor for small distributed USB based sensor/control networks.
Both USB and Ethernet have advantages when designing distributedsensor / control networks,” says Gregori. “The primary advantage forUSB is power distribution and network cost. Power distribution is builtinto the USB specification, 100ma per device, or 500ma per device forpowered hubs (with software negotiation). The power distribution systemis built into the cabling, hubs, and hosts. Another advantage is lowcost USB devices. A variety of low cost USB devices designed to beconnected to a PC can be used in the sensor network.”
The advantages of Ethernet, he says, are performance andcompatibility. Ethernet and TCP/IP enabled sensors do not require agateway to connect to a PC LAN network. This makes the sensor datasignificantly easier to get to the internet for remote monitoringaround the world. WiFi compatibility is also an advantage if the sensornetwork is within range of a existing WiFi network.
“When designing a sensor / control network for a device that willhave a local controller ( for instance a manufacturing machine ) a USBnetwork is a good option,” says Gregori. “Assuming the sensors drawless then 100ma, the USB wiring can be used as the power distributionnetwork, eliminating the additional cost of power wiring.
But he points out that when designing a sensor/control network for adevice that will be remotely monitored or controlled, an Ethernetnetwork is a good option. “In most cases, the PC LAN network in thebuilding can be used as a connection to either a remote node in thesame facility, or a remote node on the internet.”
Wireless connectvity's multiplechoices
For a connectivity protocol that was still in an embryonic state in thelate 90s, the potential of the IEEE 802.15.4 wireless spec in embeddedsystems designs has increased dramatically.
According to Matt Maupin, who will be presenting “
In addition, to Zigbee, he said, developers now have a choice ofwireless control alternatives, including the Freescale Synkronetworking protocol, WirelessHart, and the SP100/ISA100.11a networkstack, 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,” saysMaupin. “The two key factors to look at are cost and the target market(consumer, commercial and industrial) as these factors tend to be atopposite ends. For example, if a solution is built for the industrialneeds, the cost tends to go up. At the same time, to keep the consumerdevice cost down, features and flexibility are often stripped out.
Synkro technology, he says, targets consumer devices and has beendeveloped with cost in mind. From a silicon standpoint, the ICs can besimplified to remove much of the I/O while memory is the least requiredof all stacks discussed. This allows smaller ICs with less memory to bedeveloped to address this specific market.
ZigBee technology is the next market up, and in general has thelargest market appeal. “However, it fits best in the commercial space,” says Maupin, “but does not fit as well into the low end consumer dueto cost, and is generally not perceived as an industrial fit due tolack of features such as channel hopping.”
ISA100.11a and WirelessHART technology are both targeted toward theindustrial market, but the mandatory 10ms time slot and 10dBm poweroutput for WirelessHART specification will slightly increase the costover ISA SP100.11a technology.
In both cases, he says, another cost is likely to be the stackitself. While ZigBee and Synkro networking protocol are developed bythe IC makers and usually provided at no cost, it is likely thatSP100.11a and WirelessHART specification will have additional costassociated with them for the stack, adding to the overall product cost.
“While there is still no 'One Size Fits All',” says Maupin, “thevarious protocols still benefit from many of the key technical andmarket advantages of 802.15.4, such as lower cost, increased vendorselection, and competitive enhancements”
How much intelligence, and where?
“As sensor-based applications rapidly increase in complexity, itbecomes imperative to embed a greater degree of intelligence to thesensor interface,” says Sinha. “Many applications utilize multiplesensors to obtain a variety of measurements and process them in highlyinnovative ways. In some cases, the signals from multiple types ofsensors must be processed simultaneously (and therefore by the sameMCU), a scenario that can be termed “sensor fusion.”
Each type of sensor has its own signal characteristics and requiresa different set of post-processing to extract useful information fromit, which increases the amount of CPU computations and peripheral datahandling.
Also, in many applications, says Sinha, sensors are physicallydispersed over a wide area, such as in a large building or factory, orin various parts of an automobile. A centralized processing/controlapproach often proves ineffective, or inefficient at best, for suchdistributed systems.
“To offload some of the processing and data-storage requirementsfrom the central control unit, it is beneficial to spread theprocessing capability over multiple MCUs located close to, or evenintegrated with, the sensors,” he says. “This 'distributed sensorprocessing' approach requires a variety of powerful signal-conversionand communication peripherals.”
More connectivity options
Other useful ESC classes on embedded wired and wireless networking andsensor design include:
To attend these and other informative classes,