Rosewill RPLC-201P Uživatelský manuál stáhnout pdf (Strana 5)

CIRCUIT CELLAR • MARCH 2014 #284

TESTS & CHALLENGES

Sponsored by WIZnet — circuitcellar.com/wiznet2014

into the microcontroller itself, so you’ll have

to conjure up some external memory if you

want to spice things up.

The most popular add-on is a MicroSD

card, which, like the W5500, uses a SPI

bus so you just need one extra pin for chip

select. Using a standard file system driver

(e.g., FAT), you can actually do much of the

development and testing of your “website”

on a PC. Then when you’re finished, just plug

the SD card into your IoT gadget.

For prototyping, check out the WIZnet

ioShield (see Photo 7), which is a baseboard

for the WIZ550io that includes an SD card

socket. There are ioShields for diﬀerent

platforms (e.g., Arduino, LaunchPad,

mbed, etc.), and with 0.1” headers they are

breadboard friendly.

PRESTO, CHANGE-O

Since your browser is a “client,” it makes

sense that every IoT gadget should be a

“server,” right? Not necessarily. Being a server

typically implies being open for service 24/7,

but many IoT applications (e.g., my garage

“Thing”) are characterized by intermittent

low duty-cycle activity. And while running

on a LAN works ﬁne, there may be issues

reaching an in-house server from the WAN

due to ﬁrewalls, ISP restrictions, changing IP

addresses, and the like. Besides, do you really

want to let the outside world anywhere near

your LAN? Maybe it makes more sense for IoT

gadgets to be clients.

But how do you get two clients (i.e., IoT

device and browser) to talk to each other?

The answer is you stick a server in between

them courtesy of a “Device Cloud” provider

such as Xively (formerly Pachube), Exosite,

Devicehub.net, ThingSpeak, Nimbits, XOBXOB,

the list goes on and on. (Postscapes provides

an extensive list, see Resources.)

As much as the WIZnet chip oﬄoads

network chores, these services handle data

storage and visualization to make life easy

for the IoT application. Just send your raw

data and the service will archive it, present it

to a browser as a graphical chart, and send

an e-mail, text, or Twitter alert if you like.

Better yet, you don’t need any specialized

web programming tools or know-how to get

something useful working quickly.

The technical capabilities and look and feel

of each device cloud service diﬀer, as do their

business models, everything from for-proﬁt

and pay-to-play to free and open source. But

from 50,000’ all work in a similar way. To send

data to the cloud, the IoT client hits the cloud

server with a request that carries the data

(e.g., variable name and value) in the URL or

the request body. To get data from the cloud,

the IoT device sends a request specifying a

variable and then retrieves the data from the

server response.

I decided to get my head in the clouds

by prototyping a client version of my garage

door “Thing” (see Photo 8) using an Arduino

+ a WIZ550io connected to Exosite.

Note I’m powering the WIZ550io from the

Arduino 3.3-V supply. That works for newer

Arduinos (e.g., my UNO R3) that have a

150-mA, 3.3-V regulator. To work with earlier

Arduinos or clones that only specify 50 mA,

a real “shield” (e.g., the WIZnet ioShield) will

include a 3.3-V regulator running oﬀ the 5-V

supply.

PHOTO 8

A prototype of the client version of my garage “Thing” is shown.

circuitcellar.com/ccmaterials

RESOURCES

T. Cantrell, “I-Way the Hard

Way,” Circuit Cellar 135, 2001.

———, “Weatherize Your

Embedded App,” Circuit Cellar

273, 2013.

S. Foskett’s blog, “Power Over

Ethernet Calculator,” http://

blog.fosketts.net/toolbox/

power-ethernet-calculator.

Postscapes, “IoT Data Broker and Cloud Service

Providers,” http://postscapes.com/companies/

iot-cloud-services.

WIZnet, “Connect the Magic,” http://j.mp/

ConnectTheMagic.

SOURCES

Exosite Device Cloud

Exosite | www.exosite.com

RPLC-201KIT AV adapter starter kit

Rosewill, Inc. | www.rosewill.com

TL-WR702N 150 Mbps Wireless N NanoRouter

TP-Link Technologies, Co. | www.tp-link.us

W5500 Ethernet controller

WIZnet | wizwiki.net

ABOUT THE AUTHOR

Tom Cantrell (micro

[email protected]) has been

working on chip, board,

and systems design and

marketing for several

years.

Subscription: http://circuitcellar.com/subscription/

1 2 3 4 5 6

Komentáře k této Příručce

Žádné komentáře

Rosewill RPLC-201P Uživatelský manuál Strana 5

Komentáře k této Příručce