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 and interfacing
» No need for any special device drivers or software programs to be loaded onto the PC
» Existing application software can be used with no need for modification
» Most wedges 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:

» The scanner/wedge 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
» Wedges are 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 cable.

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 new cable/interface.

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" connection.