How do I connect a bar code reader/scanner to my PC ?
Connecting a bar code reader to a desktop PC is actually a lot easier
than many people at first think. By far and away the easiest and
most popular way to connect wands and scanners is to use a device
called a keyboard wedge interface, generally abbreviated to "wedge"
interface. A wedge interface is a small device that is attached
to the keyboard socket on the PC base unit. The keyboard is plugged
into the wedge, as is the bar code wand or scanner. The keyboard
continues to operate in the usual way and its operation should be
completely unaffected by the presence of the wedge.
When a bar code is scanned the wedge receives the signal from the
wand, decodes it and then sends the decoded output to the PC by
emulating the appropriate keyboard strokes. In most cases the end
of the bar code string is indicated by the wedge sending a carriage
return (CR) keyboard stroke.
The major benefits of wedges are
Ease of connection
No need for
any special device drivers or software programs to be loaded onto
software can be used with no need for modification
and scanners can usually be adequately powered from the keyboard
line power coming from the PC, so no special provisions need to
be made to power the scanner
Potential downsides/limitations that may need to be considered
in some cases
combination will always be on and available, so if the user scans
at the wrong time or the wrong place in the application, the bar
code data will still appear as if typed in at the keyboard
almost invariably not suitable for laptop or notebook PCs. Many
laptop PCs will disable their built-in keyboard if the unit senses
any devices attached to the external keyboard port. There are however
some specially designed scanners for use with laptops. Alternatively,
those with modern laptops with USB ports should select a scanner
with a USB interface.
As long as these two considerations do not pose a problem, then
a keyboard wedge is a simple and cost effective way to connect a
wand or scanner. A further option that does sometimes offer potential
cost savings is to purchase a scanner that has the PC wedge built
into it already (instead of having a separate wedge). These devices
usually terminate in a Y type connector to plug directly onto the
PC socket on one side and an in line socket to take the keyboard
I want a bar code reader for my PC, but I also want to plug
one into a hand held computer.
Can I buy just one reader and swap it between them ?
The answer usually depends on exactly what plugs and interfaces
are involved and the type of wands or scanners to be connected.
Different types of plugs and connectors, with the possibility of
having to set scanners to different configurations for different
devices, generally make it too complicated for easy and practical
"swapping" from one device to another.
The only real exceptions to this are scanners that have been specifically
designed to allow cables to be swapped, then the scanner can be
reprogrammed to connect to a different device - but here again the
scanner usually requires some re-configuration to work with the
The general problem is exacerbated by the fact that there is no
universal industry standard for bar code connectors. Over the years
different manufacturers have adopted different types of plugs and
connectors with varying pin connections and configurations. The
9-way D style connector has emerged as a rough (but by no means
certain) standard, but pin connections still vary widely! If you
are ordering a wand or scanner to connect to a host device you already
have, you may need to give your supplier details of the connector
and pin-outs on the host device - look in the product's manual or
technical guide if necessary.
I have an RS232 based terminal. What's the best way to connect
a wand or scanner ?
It is possible to purchase keyboard wedges that will work with terminals.
The major problem here is again the lack of standards. Different
terminals behave very differently with many variations of the keyboard
scan-codes for different characters (scan-codes being the electronic
codes the terminal sees when a key is pressed on the keyboard).
Even within some terminal manufacturers' own product ranges the
scan-codes can vary significantly. So accuracy of information about
the host terminal is critical. However, if the terminal model is
precisely specified, it is usually possible to find a scanner to
work with it - unless it's a very old or unusual terminal. These
configurations sometimes also need the scanner to have a separate
power supply, sometimes referred to as a "power injector"