Which Bar
Code Scanner Interface is right for me? RS232, Keyboard,
or USB.
When you purchase a bar code scanner, the most
important decision that you will need to make is how to interface
the bar code scanner to your computer.
Modern bar code scanners are normally available with one
of three "output options" - either "Keyboard
Wedge" output, RS232 serial output, or USB output. The
following is a description of each of the three output options
and how they work and the differences between them. Which
option you choose will depend mostly on the software that
you will be scanning the bar codes into an how you want everything
to work as well as the types of ports available on your PC.
Keyboard Wedge Output
The "Keyboard Wedge" output option is the most
common option. To interface a keyboard wedge bar code scanner
to a PC, you would disconnect the keyboard from the keyboard
port on the PC, plug the bar code scanner directly into the
keyboard port and then connect your keyboard to a small "jumper
cable" on the end of the bar code scanner cable (so
that you do not lose the functionality of your keyboard).
In other words, you are connecting the bar code scanner in
the line between your keyboard and you PC. (One benefit of
this is that the bar code scanner gets its power from the
keyboard port so you do not need to connect any type of power
supply to the scanner.)
When you scan a bar code with a keyboard wedge scanner, the
data that is encoded in the bar code goes into the PC through
the keyboard port so that it appears to whatever software
is running in the PC as if it were being typed in on the
keyboard. (i.e. The bar code scanner behaves exactly like
a second keyboard connected to the PC.)
With a keyboard wedge scanner, you do not need any additional
software. You simply plug the scanner in and start scanning
bar codes. The keyboard wedge interface is extremely simple
and in most situations, you do not need to make any changes
to the software that you will be scanning the bar code data
into.
The main advantage of the keyboard wedge interface is that
it works just like a keyboard. You put the cursor where
you want the bar code data to go and then scan the bar
code and
the data pops in just as if you typed it on the keyboard.
The disadvantage of the keyboard wedge interface is that
it works just like a keyboard. If the cursor is not in
the correct input field in the correct application program,
then,
when you scan a bar code, the data still gets entered into
the PC as if it is being typed in on the keyboard. If the
cursor is not in the right place or if the application
that you want the bar code data to go into does not have
the input
focus, the data goes to the wrong place or possibly the
wrong application program. Also, if you need to modify
the data
in any way before it goes into the application program
running in the PC, you cannot do this. For example, suppose
that
you need to parse the bar code data so that separate parts
of the data goes to different input fields or if you want
to add a date or time stamp to the bar code data, it is
not possible with a keyboard wedge scanner.
RS232 (serial) Output
The RS232 output option means that you would connect the
bar code scanner directly to an available RS232 serial
port on the back of your PC. (RS232 output scanners also
normally require an AC adapter to supply power to the scanner
because the RS232 port cannot supply enough power to run
a bar code scanner.)
With a RS232 output scanner, you would also need to either
develop your application software to open and read in data
from the RS232 serial port directly or use a software interface
like the TALtech WinWedge software products. (http://www.taltech.com/products/winwedge.html)
The main advantage of the RS232 output option is that you
can develop your application so that it does not matter
where the cursor is. When you scan a bar code, the data
always goes to the correct place in your application program
because the data from the scanner is going directly into
the application program and is not going through the keyboard
port. The RS232 interface requires a little more work up
front because you either need to develop your software
to work directly with the RS232 port (or configure the
WinWedge software to act as the interface between the RS232
port and your application software) however the advantage
to this approach is that you end up with a much more robust
application that does not rely on the user making sure
that the cursor is in the correct place in your application
program before scanning a bar code. If you need to create
a bar code application that is completely "idiot proof",
then the RS232 interface option is by far the best choice.
The RS232 output option also makes it possible to manipulate
the data that you receive from the bar code scanner before
writing the data to the application program where you want
the data to go. For example, if you want to parse the bar
code data or add a date or time stamp to it, the RS232
serial output option would allow you to do this.
One issue that you may run into is that some newer desktop
PCs and almost all new laptop computers do not come with
any RS232 serial ports. The problem is easily solved by
purchasing an "Add-on" RS232 serial adapter for
the PC. There are even add-on RS232 serial adapters available
the connect to a USB port on a PC. A single port add-on
serial adapter that connects to a USB port should cost
no more than $30 and you can find them at any computer
or office supply store.
USB Output
Bar code scanners that have a USB output can work one of
two ways.
The first is that they can work exactly like a Keyboard
Wedge scanner and the second is that they can work exactly
like a RS232 serial output scanner.
When you purchase a bar code scanner that has a USB output,
you normally will also need to specify which interface
you want - either "USB Keyboard Wedge" or "USB
RS232 serial port". (Some bar code scanners are only
available with the USB Keyboard Wedge option).
USB Keyboard Wedge Scanners
A USB Keyboard Wedge bar code scanner works exactly like
a "Keyboard Wedge" bar code scanner except that
instead of connecting the bar code scanner to the keyboard
port on the PC, you plug it into a USB port. When you do
this, the bar code scanner is recognized by the PC as a
second keyboard device and when you scan a bar code, all
bar code data goes into the PC just as if it were being
typed in on a keyboard. Just like a standard keyboard wedge
scanner, no additional software is needed. Windows will
automatically recognize the scanner and treat it as if
it were a second keyboard connected to your PC.
Since the USB Keyboard Wedge option works exactly the same
as a standard Keyboard Wedge bar code scanner, there is
really little difference between the two other than the
port that you plug the scanner into. USB scanners all get
their power from the USB port so you do not need an additional
power supply. The only real advantage to a USB Keyboard
Wedge scanner over a Standard Keyboard Wedge scanner is
when you need to connect the scanner to a laptop computer
that does not have a keyboard port.
USB RS232 Serial Scanners
A scanner that has a USB RS232 serial interface will come
with a special "Driver" program that you will
need to install in the PC that you connect the scanner
to. The purpose of the driver is to create a "Virtual
RS232 serial port" that works exactly like a physical
RS232 port.
After you install the driver that comes with the scanner
and connect the scanner to a USB port on your PC, Windows
will think that it has a new RS232 serial port and any
serial communications software (including WinWedge) will
be able to open this "Virtual RS232 serial port" just
as if it were a standard RS232 serial port built into the
motherboard of the PC.
In other words, the scanner works exactly like a RS232
serial output scanner except that it connects to the PC
through the USB port. Everything that was said above in
the paragraph about RS232 serial output scanners applies
to a USB RS232 serial scanner. The only difference between
the two is that the USB RS232 serial scanner plugs into
a USB port on the PC instead of into a RS232 serial port.
This means that your PC does not need to have any RS232
serial ports installed in it and it also means that the
bar code scanner will get its power from the USB port therefore
you do not need any additional power supply.
A USB RS232 serial bar code scanner is basically equivalent
to a standard RS232 serial scanner that comes with a built
in USB RS232 add-on adapter with the advantage that you
do not need an external power supply.
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