We’re at the dawn of a new era in connectivity
and convenience unlike anything we’ve expe-
rienced before. The Internet of Things (IoT)
promises to deliver on the vision of
anywhere/anytime knowledge and control of
our home and work environments, and de-
pending on which side of Geoffrey Moore’s
“chasm” you sit, the IoT may already be here.
Today I can monitor my connected home and
ensure my family is safe, optimize my home
energy usage and check on my pets, all while
at home or on the road. There will be a tipping
point, a handful of innovative consumer prod-
ucts and services that even the late adopters
won’t be able to ignore, after which there will
be little question that the IoT has arrived.
If it hasn’t already happened, soon your com-
pany management team will propose products
to participate in the IoT. How will you respond?
The good news is that many of the application
building blocks for the IoT are available today,
just waiting for you and your team to add
your creative genius. We all want to be in con-
trol of the security of our home and family,
and it only takes a fire or burglary to remind
ourselves of this need. A number of upstarts
and cable operators have introduced products
for the connected home that provide fire, se-
curity and convenience services. A typical con-
nected home system architecture comprises a
number of sensor nodes ranging from simple
to complex, a wireless network featuring a
gateway to connect to the Internet wirelessly
and potentially provide localized system intel-
ligence, and cloud services to connect to mobile
devices. Figure 1 shows such a connected home
architecture.
Embedded systems designers must consider a
number of competing requirements in de-
signing a gateway or sensor nodes, such as
processing speed, memory size, regulatory
considerations, energy consumption, system
latency, connectivity options, system segmen-
tation, security requirements, interoperability,
future migration and system cost, to name a
few. The system gateway might be a cable set-
top box or a standalone system. See figure 2
for an example of a typical gateway architec-
ture. The gateway microcontroller (MCU) is
most likely based on an ARM Cortex-M or
Cortex-A class processor combined with con-
nectivity options such as Ethernet, Wi-Fi, Zig-
Bee and sub-GHz/ISMwireless. Considerations
for selecting the optimal MCU include mem-
ory size and processing requirements for the
communications stacks and gateway services,
system latency requirements for “real-time”
or offline operation, and connectivity. Con-
siderations for selecting the RF subsystem in-
clude local regulations (FCC, ETSI, etc),
whether connection to a broader ecosystem is
desired (which requires a standard) or if the
system will be self-contained (a proprietary
stack can be used), protocol stack requirements,
link budget (which translates into RF range)
and system cost. Wireless transceiver energy
consumption is relevant to the system archi-
tecture since it affects sensor node range and
battery lifetime.
A “thin” gateway that only passes sensor and
environmental data via Ethernet or an RF sub-
system to the cloud could suffice with a smaller,
less expensive Cortex-M class MCU, particu-
larly if the communications stack requirements
are kept minimal. The advantage of a thin
gateway is that intelligence and interoperability
between nodes can be managed by cloud serv-
ices, but the disadvantage is the potential for
round trip while waiting for cloud services to
process and return command and control data.
At the other extreme a “smart” gateway provides
the command and control intelligence onboard
and has the advantage of minimal latency and
full functionality if the cloud connection is
lost. However, smart gateway applications must
manage the business logic and must be future-
proofed to support system upgrades. Nobody
wants to buy a wireless lighting control system
today that requires a new gateway tomorrow.
The basic connected home node might be a
door sensor, wireless light or a smoke detector,
as shown in figure 3.The MCU is likely to be a
Control and connectivity options
for the Internet of Things
I
NTERNET
-
OF
-T
HINGS
By Greg Hodgson,
Silicon Labs
Well designed,
innovative IoT connected devices,
apps and cloud services
will drive the IoT revolution,
in turn requiring IoT
end nodes and gateways
combining energy efficiency,
performance, and cost-effectiveness
regardless of MCU bit size.
This article examines common
architectures to navigate the IoT.
Figure 1. The connected home
June 2014
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