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TESTS & CHALLENGES
Sponsored by WIZnet — circuitcellar.com/wiznet2014
100 m) and/or high-current loads. Use a “PoE
Calculator,” such as the one available from
Stephen Foskett’s blog (see Resources), to
estimate the voltage drop depending on your
cable length and current requirements
Or just wire everything up and dial
it in using a variable power supply while
measuring the actual voltage at the far
end. Make sure your device is attached and
fully active (i.e., pulling maximum expected
current, not sleeping, etc.) to get an accurate
voltage reading.
MIND READER
If your heart is set on wireless, you can
always add a low-cost Wi-Fi adapter. The
TP-Link NanoRouter I’ve been using (see
Photo 5) is quite versatile with five different
configuration options: Router, Access Point,
Bridge, Repeater, and Client. Your attached
Ethernet device can either join an existing
wireless network or you can create an
additional network with its own SSID.
Thanks to the march of technology, the
dual Ethernet + Wi-Fi approach is getting
more affordable. The WIZnet online store has
the WIZ550io for $18 (the W5500 chip costs
just $2.87) and you can find TP links online
for $20 or so. By comparison, if you Google
“embedded Wi-Fi module” or “Wi-Fi shield,”
you’ll see a variety of different products
ranging from around $20 for a bare Wi-Fi
module (no PCB) to $80 for an official Arduino
WiFi Shield.
Indeed, the large variety of Wi-Fi solutions
doe
s have a downside. There are more than
a few embedded Wi-Fi chipsets in popular
use (e.g., Broadcom, GainSpan, Microchip
Technology, Texas Instruments, no doubt
more on the way), each with their own
capabilities and unique commands. The
prospect of trying to write and support
drivers for all the Wi-Fi chipsets across all the
popular platforms gives me a headache. With
the dual approach, it’s easy to move Ethernet
apps (any app, any platform) to Wi-Fi. Just
plug into the TP link and you’re done without
changing a line of code—that’s the kind of
magic trick I like!
SERVER UP MY SLEEVE
Everyone wants to be master of the
IoT universe from their browser screen.
With assistance from WIZnet, even tiny
microcontrollers can run a simple web server.
Check out the webpage served up by my
garage door “Thing” (see Photo 6).
But you can see the problem; or rather
you can’t see it. Where are the high-
resolution graphics that a pixel-jaded
populace demands? No way to cram more
than a bit of HTML/JavaScript/JPG eye candy
PHOTO 5
Low-cost mobile hot spots such as this TP-Link NanoRouter make it easy to convert Ethernet to Wi-Fi without
any software changes.
PHOTO 6
My garage door “Thing” doing its thing.
PHOTO 7
If you want a fancy server with lots of eye candy, a microSD card is the way to go. The WIZnet ioShields
include the card socket and are available for various platforms. The Arduino version is shown here.
Copyright © 2014 by Circuit Cellar, Inc.
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