-May 2009-
-Circuit Cellar Magazine Reader Survey
ESC
Title Bout
By Tom Cantrell, author of Circuit Cellar’s “Silicon Update” Column
With all the macroeconomic angst and headline gloom and doom, I was afraid this year’s Embedded System Conference in Silicon Valley might be a somber affair. But I was pleasantly surprised. Behind the bailouts, the Silicon Wizards are working hard to deliver the new technology that will drive the next wave of deeply embedded innovation.
ESC is an opportunity to chat with really smart people. It’s all the better when I bump into Circuit Cellar readers who invariably have something interesting to say. One longtime reader was kind enough to say he enjoys reading my columns and gets a kick out of the way I turn a phrase in my titles. That gave me the idea of reusing a lot of those past titles in this ESC round-up. Kind of a reminder that the challenge of delivering more for less never ends. So let’s head back to the future.
LIQUID CRYSTAL DELIGHT (CIRCUIT CELLAR 132, 2001)
A lot of designers want to put a pretty face on their embedded designs using a fancy (e.g., 1/4 VGA+) LCD—all the all the better if it has touch screen capability. You can redesign from the ground up, but in many situations, it’s easier and less risky to retrofit an intelligent graphics subsystem to an existing design.
Amulet offers a highly integrated chip that fills the bill. Just add glass, and voila, instant eye-candy (http://www.amulettechnologies.com/products/starterk.html). Well, not quite. There’s still the small matter of all the software to deliver the glitz. A typical LCD subsystem comes with a library of graphics primitives (draw, fill, paint, etc.). Indeed, the Amulet GUI chip comes with that option (i.e., built-in graphics primitives that are manhandled via UART connection to your design).
But Amulet’s real claim to fame is a different scheme that exploits the ubiquity of HTML. The idea is that you can use standard web page authoring software (e.g., Dreamweaver) to craft your display as a virtual “web site.” Indeed, the final step in the process simply has you point the Amulet “micro-HTML” compiler at the INDEX.HTM file comprising your screens and it handles the rest.
Make no mistake: it doesn’t support all HTML features of a full-fledged web
browser, and the best results will be achieved by folks who know how to get
under the hood with HTML and web-authoring software. But that’s probably as it
should be considering the artistic skill required to make an impression. I had
a chance to play around with Amulet’s starter kit and can attest it has the
attention-grabbing FX and “widgets” your app needs to standout from the
4-line-by-20 crowd.
As an aside, Amulet’s fancy graphics chip comes courtesy of a
CAP7L customizable SoC from Atmel. The CAP7L combines a full-featured hard-core
ARM7 MCU with 200,000 gates of metal-mask programmable logic. Minimum order
quantity is just 10,000 units with turnaround as fast as 12 weeks. A low
$75,000 NRE supports fully amortized unit costs as low as $5 (and there’s no
separate ARM license fee). You can even use a low-cost FPGA tool chain to
develop (and prototype with Atmel’s FPGA-based starter kit) your custom logic
(http://www.atmel.com/dyn/resources/prod_documents/doc5215.pdf).
It’s not often you’ll find me using words like “quick,” “easy,” and “cheap” in the same sentence with “ASIC,” but CAP7L comes real close.
-NEXT-
EQ Interactive
Problem: One way to
drive the transformer primary in a switchmode power converter is to connect the
DC input to the center tap and alternately pull the ends of the winding to
ground with power transistors, as shown below. This approach has the advantage
of simplicity, but there are some pitfalls to watch out for. For example, what
is the voltage rating required on the transistors? Why?
Think You
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Solution: The basic
voltage rating of the transistors must be greater than two times the input
voltage, because when one end of the primary is pulled to ground, the other end
swings up from the supply voltage by the same amount through basic
autotransformer action.
Furthermore,
any “leakage” inductance—less than 100% mutual coupling between the two halves
of the primary—will cause inductive spikes above that nominal peak value when
each transistor switches off. There needs to be a way of clamping or snubbing
these spikes.
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