| The most common situation is
in a warehouse where someone is walking around collecting
inventory data with a handheld
scanner and having a cable attached to that scanner back
to a PC would be impossible. There are many other situations
though. I was asked recently about a clean room where someone
needed to install a laboratory balance in a clean room and
be able to send weight readings to a PC located outside the
clean room. Running an RS232 cable was out of the question
because that would require drilling a hole through the wall,
which would compromise the "cleanliness" of the
room.
The solution is to use wireless systems. There are currently
three widely available technologies for wireless RS232 communications
and one up and coming one:
1) Serial Infrared (SIR)
2) Wireless RS232 transceivers (i.e. radio modems)
3) Wireless Ethernet with an appropriate RS232 to Ethernet
converter.
4) Bluetooth Serial.
1) Serial Infrared uses a device called an infrared transceiver
to encode and transmit RS232 data signals over a beam of
infrared light similar to the way your TV remote control
works. Each device is plugged into a transceiver and the
two transceivers must be in each other’s line of sight.
The transceivers must also be relatively close to each other,
typically under three feet away. Serial Infrared is the least
expensive of all the wireless technologies however it is
also the least reliable, has the shortest range and is the
most prone to problems. If you obstruct the beam, you lose
the connection.
If you do a good search on the web, you will find several
SIR transceivers available for under $70 per transceiver.
Since you have to be in the line of sight as well as under
three feet away, SIR just never caught on in a big way. Under
most circumstances it is much easier to connect a cable than
use SIR transceivers.
2) The most common of the three technologies for wireless
RS232 data transfer are radio modems. Radio modems are similar
to SIR transceivers in that they connect directly to the
serial ports of the two devices that need to communicate.
You simply plug a radio modem into a serial port on your
PC and another one on the device that you want to capture
data from and use radio signals to send data instead of running
wires.
Radio modems are available from a number of different manufacturers
with a wide range of specifications. The most important specification
is how far you can transmit data. Many different systems
are available with working ranges from 100 feet up to several
miles. The typical cost for a pair of radio modems with a
range of between 500 to 10000 feet is around $500 to $1000.
Some high-end bar code scanners come with built-in radio
modems to allow wireless bar code data collection from a
simple hand-held device.
One variation on the Wireless modem theme is a device called
a cellular modem, i.e. a modem and a cell phone combined
together into a single unit. Cellular modems are most commonly
used for connecting laptop computers to the Internet. Cellular
modems have the advantage that they can send data anywhere
within the range of a cell phone system however they have
the drawback that they are not as easy to use (one device
has to “call” the other to establish a connection)
and you must also subscribe to a cellular service and pay
a monthly fee for each modem.
3) The most interesting as well as the most promising of
the wireless options is to use a wireless network system
to send and receive serial data. With the advent of “WiFi” wireless
networking protocols, a number of companies have come up
with devices called “Wireless Serial Servers” that
allow you to connect RS232 serial devices directly to a
wireless network. Traditionally, a serial device server
is a small box with a RS232 serial port on one side and
an Ethernet port on the other. You connect the serial device
to the RS232 serial port on the device server and then
connect the device server to your Ethernet network. Instead
of using an Ethernet cable connection to a network hub,
the wireless serial servers establish a wireless connection
to a WiFi wireless network base station. The range of most
WiFi systems is between 60 to 750 feet depending on the
environment and the types of obstructions between the transceivers.
Most wireless serial device servers come with a software
device driver that you install in your PC that will make
the serial port on the device server appear as if it were
a built in RS232 port on the PC (i.e. they create a virtual
serial port on your PC, much as TCP-Com from TALtech does).
This makes it possible to use standard serial communications
software to open the ports on the wireless device server
just like you would open a built in COM port.
For more information about serial device servers and TCP-Com
please visit http://www.taltech.com/products/tcpcom.html.
5) Another exciting new system for wireless communications
is the Bluetooth Wireless system. This is the Up and Coming
one mentioned above. Bluetooth serial is fairly new and the
prices have not dropped to what they should be yet and there
are also not that many manufacturers of Bluetooth serial
hardware however I expect that this will change quickly.
You can now purchase Bluetooth Wireless RS232 adapters that
basically behave just like standard RS232 serial ports on
a PC except that there are no wires. You need a Bluetooth
receiver on the PC side connected to a USB port on the PC
and then you simply use a Bluetooth Wireless RS232 adapter
on the end where you connect the device that you want to "go
wireless" with.
Do a search on Google for "Bluetooth Wireless RS232" or "Bluetooth
Serial" and you will find a number of companies that
are selling or developing this type of hardware.
Bluetooth has a much shorter range than WiFi however you
can get up to 100 meter range with Bluetooth Class 1 devices
(Class 2 devices are limited to 10 meters).
The most exciting part about Bluetooth serial is that when
a Bluetooth serial device comes within range of a PC that
has a Bluetooth transceiver, the PC simply thinks that it
has another serial port. The Bluetooth drivers create a "Virtual
COM port" on the PC automatically and this virtual COM
port works just like a built in COM port.
The new Bluetooth
Wireless VoyagerBT - Bar Code Scanner manufactured
by Metrologic will be released in time for Frontline Expo
in September 2004. This transmits decoded bar code data back
to a base station using Bluetooth wireless technology. From
the base-station the data is input into the PC via the usual
RS232, keyboard wedge or USB interfaces. If you have a Bluetooth
receiver on your PC you can bi-pass the base station and
input data directly into the PC. This new scanner also supports
reading and decoding the new RSS14 bar code symbology. Read
more at http://www.taltech.com/products/VoyagerBT.html
For a list of companies that sell wireless RS232 hardware,
see http://www.taltech.com/resources/links.html#Wireless.
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