18 12-2011 elektor
ANDROID-TABLETS
the tablet. The tablet also has high process-
ing power and large memory capacity. How-
ever, real-time applications are not possible.
The main reason for placing the intelligence
in the connected microcontroller is that the
application requires real-time control of the
circuitry and/or short response times.
In practice a hybrid solution will usually be
the most appropriate choice, with the app
that runs on the tablet handing the tasks
closely related to the peripheral devices of
the tablet, while the connected microcon-
troller provides direct control of the I/O.
Applications
To give you an idea of the realm of possibili-
ties, here we outline a number of potential
applications and briefly describe the neces-
sary architectures:
• Data logger with configuration set-
tings entered over the GUI. The data
can viewed in graphic form on the GUI
or on a web page. The raw data can be
uploaded over the Web or via FTP. The
hardware requirement for this is an ADC
connected to the USB port. On the soft-
ware side, three apps would be necessary:
a web server and an FTP server (both of
which are available as standard apps), and
a user-written app for reading and storing
the data — plus a configuration settings
screen and graphic output.
•Telemetry from a (race) car, with live data
displayed on the GUI and 3G link capabil-
ity for reading out data in real time and
storing it on a flash memory card. This
requires a USB to OBD2 interface and
software to handle the interface, config-
uration settings, and data readout and
storage. If the data only needs to be read
out once per lap, a standard FTP server
app would be sufficient. If real-time or
near real-time readout is required, a new
app must be developed for this purpose
(perhaps based on a serial communica-
tion app).
•Home automation: controlling a solar
water heater and a central heating sys-
tem with the aid of weather forecasts on
the Web, with remote control via a web-
site and a GUI on the tablet. This requires
the same configuration as the data log-
ger mentioned above. An additional
feature here is that decisions regarding
how the solar water heater is used can
be taken based on information available
on the Web, such as the forecast hours
of sunshine and outdoor temperatures.
This requires writing a special app to
obtain this information, for example by
reading RSS feeds and extracting the
necessary data.
•Digital oscilloscope with settings and
waveform display on the GUI, and poten-
tially the ability to send oscillograms by
e-mail. The configuration described for
the data logger is necessary here as well. In
this case this case the majority of the intel-
ligence must be located in the connected
circuitry due to the required signal speeds.
•A coffee machine control panel that sends
an e-mail to the maintenance department
when the coffee needs to be refilled or
a problem occurs. Here the tablet can
serve as the heart of the system, but I/O
circuitry is necessary for controlling and
reading data from all of the components.
•A standard maintenance console. A tab-
let is very suitable for use as an external
console for troubleshooting, configu-
ration and maintenance. In its simplest
form it can communicate with the target
system over the USB port, using a termi-
nal emulator app on the tablet. This could
be used to view start-up messages or dis-
play the commands sent from the termi-
nal. A more complex option is a console
connected over a USB to JTAG converter.
Thanks to its low cost, a console of this
sort could kept on hand at every cus-
tomer site.
•Prototyping: the ease of writing apps
makes a tablet suitable for develop-
ing prototypes and proof-of-concept
designs quickly and efficiently. Thanks
to the large number of standard func-
tions in Android and the wealth of avail-
able apps, considerable functionality
can be deployed in a very short time.
Conclusion
Low-cost tablet computers can be effec-
tive, affordable and quickly implementable
components of electronic projects. In addi-
tion to a visually attractive design, they
have many readily accessible functions.
At present it takes a good deal of effort to
use the tablet’s USB port for connection to
external circuitry, but with the advent of
Android version 4 in the coming year this
will become easier. This will open the way
for a host of new applications.
(110667-I)
Internet Links
[1] www.elektor.com/110265
[2] www.amarino-toolkit.net
[3] www.microchip.com/android
[4] http://developer.android.com/guide/
topics/usb/accessory.html
Figure 2. The Android API is extensively
documented.
Figure 3. Using a tablet in a home
automation system.
我的内容管理
展开
