Image Processing Reference
In-Depth Information
thatthesizeofonespeciiccomponentcanforceacompletePCBredesigntoitwithinthegiven
dimensions. Typical components that drive the PCB design are capacitors and batteries.
Apart from component selection and integration, the form factor also has a direct influence on
the antenna design, which is very sensitive to the orientation and proximity of other electronic
components.
Appearance is everything! This actually holds true to a large extent when it comes to embedded
design of industrial WSN devices. In Section ., we find out that what counts is the “inside,” but
theappearanceofthedevice(size,shape,material,andweight)doeshaveamajorimpactontheinal
design.
27.3.4.4 Modularity
The lifetime of the devices is a key parameter to consider. The office/consumer industry is the main
driver for wireless technologies today, with high volume applications. Industrial automation devices,
however, tend to have a much longer lifetime than consumer products. his means that special care
needs to be taken when integrating wireless components into industrial devices. A modular (hard-
ware and software) design is crucial in enabling effective maintenance of devices—which are built on
standard commercial off-the-shelf (COTS) components—throughout their lifetime.
Modular design is necessary in order to reuse elements, but it might seriously limit your control
over individual HW/SW functions and thus influencing the overall sleep-wake-up scheme of your
device. Proper interfaces are thus vital to mediate between reuse and performance, something that
canbehardtoinluencewhenCOTScomponentsareused.
The form factor of commercial components or subassemblies naturally has a direct impact on the
packaging of the device, but again, the interfaces are just as important, and need to be sufficiently
general to allow portability.
One classical example of the separation of modules is the split between the communication proto-
col and the application sotware. he latter is invariably written by the device vendor, but the former
is frequently purchased from a third party. Embedding these two components onto the same micro-
controllercanbediicult.Wealsoruntheriskofsuboptimizing,i.e.,thetwosotwaremodulesare
optimized (with respect to power, performance, code size, etc.) individually. his does not necessar-
ily give a globally optimum solution. Even more complex is handling new releases, bug fixes, and
documentation when the software running on the same processor has several sources.
In addition to reuse, modularity is also a means to minimize the design risks. For example, to avoid
electro magnetic compatibility (EMC) problems in your power supply design, it is often beneficial
to buy predesigned and tested COTS components such as a DC-DC converter. If the device is going
to be produced in large volumes, the cost of these COTS components can be prohibitive though,
forcing you to make your own low-level design. Component specification can be another limiting
factor when utilizing available designs, e.g., if you require a large operating range.
The sum of the parts can equal more than the individual parts together, at least from a product
maintenance point of view. However, great care must be taken to ensure that sum of the parts also
provides adequate performance. In Section ., we cut up the WSN device into logical pieces and
look how we can put them back together again without unduly compromising the control over the
final behavior of the device (power consumption, latency, etc.).
27.3.4.5 Power Supply
The power supply is a central part of the WSN device; it is the “motor” that provides power to the
various parts of the system. The challenge is the same as the development team has regarding the
final product, to provide the right level, with the right quality, at the right time.
The design of the power supply can put direct bounds on the duty cycle of the application. For
example, in an energy-scavenging solution, the harvested energy is usually stored in an intermediate
 
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