by Bryan Bergeron, Editor
Thanks to several pervasive trends in electronics, including
increased miniaturization of components, standardization of
signal formats and levels, and economic pressure to minimize design
and construction time, there is a movement away from prototyping
with components in favor of modules. Instead of working with
individual ICs and passive components, cost- and time-conscious
engineers design and construct prototypes by working at the system
level using function-specific modules. These modules are typically
composed of ASICs with a handful of SMT discrete components
mounted on a fingernail-sized PC board to facilitate ease of assembly.
This shift toward prototyping with modules means that, for
example, instead of considering Ohms law and calculating the value
of transistor bias resistors and the like, engineers and electronics
enthusiasts are free to focus on function. If you embrace this
approach, you’ll probably find that you can design, construct, and
debug a complete electronic system in a fraction of the time it would
have taken you to build a subsystem from discrete components.
Consider, for example, the challenge of designing and constructing a prototype GPS-based navigation system for a mobile robot from
discrete components. Even if you’re facile with surface mount components, it’s likely that the switching power supply will be heavier,
require more space, and certainly require more time to construct than
the complete navigation system constructed with modules. There is
also the issue of cost. Although taking
the route of using individual components may seem cheaper at the outset,
by the time you consider the PC board,
connectors, associated hardware, and
the associated shipping charges, the
apparent cost advantage of discrete FIGURE 1
components over function-specific modules often vanishes.
Furthermore, if you have limited time to devote to electronics, using
modules may be the only practical way to accomplish your goals.
My favorite source for miniature, feather-weight modules is
SparkFun Electronics ( www.sparkfun.com). The company offers
an amazing assortment of modules — switching power supplies,
GPS receivers, Bluetooth modems, cellular transceivers, battery
chargers, and a variety of sensors — typically pictured atop a
dime or quarter. Modules from SparkFun and similar vendors
allow you to focus on functionality and exercise creativity at a
higher level. For example, if your goal is to develop a new navigation algorithm for your mobile robot, you probably don’t want
to waste time debugging the RF front end of a GPS receiver.
Instead, for about $70, you can purchase a 12-channel receiver
with built-in antenna and interface cable, shown in Figure 1.
Parallax ( www.parallax.com), maker of the modular BASIC
Stamp series, recently increased its footprint in the modular marketplace by offering a BASIC Stamp 2pe motherboard. I’ve used the self-contained, $80 microcontroller module, which includes two Atmel
AVR microcontrollers and a BS2pe BASIC Stamp SX microcontroller,
to prototype an RFID reader in less than an hour. Power is supplied
by the host computer through the
USB port, and interfacing the module FIGURE 2
to an RFID reader is simply a matter
of connecting a reader to an inexpensive plug-in I/O daughterboard on
the module, as shown in Figure 2.
The move toward modular prototyping and construction predates the development of microcontrollers and many other digital components. To illustrate the point, I
popped the cover of my Magnavox Odyssey video game system
console, shown in Figure 3. The unit, produced in 1972, is
composed of several 2” x 2” analog modules plugged into a
motherboard. Although the modules were specific to the Odyssey
and used proprietary signals and levels, they were ostensibly easier
to replace and repair than a motherboard populated with discrete
components. This advantage was never tested, however, as
the short-lived Odyssey quickly faded into obscurity with the
introduction of the Intel-based digital video games.
The modular approach to construction pioneered by
Magnavox and others has applied successfully to products ranging
from home TVs and computers to commercial navigation systems.
I can remember the distraught look on the faces of fellow technicians when the first module-based Radar systems appeared on the
market. As they predicted, Radar repair was quickly transformed
from a lucrative, all-day, on-site affair to a 10-minute card swapping
exercise that could be performed by anyone with a modicum of
diagnostic skill. Defective modules were either discarded or
shipped to a central plant where automated jigs were used to
quickly diagnose and repair defective components on the modules.
It’s important to note that working with modules doesn’t obviate the need to understand basic electronics. As Walter Lindenbach
points out in his article ‘Life of a Wire,’
the physics of individual components,
including the cables and wires used to
connect modules, can profoundly
affect circuit operation. Happy prototyping! NV FIGURE 3