Introduction to Wedges
Knowing your hardware options helps you design a reliable system that can grow with your business.
A wedge provides a technique for interfacing a bar code scanner or other input device to a host system or terminal. A wedge contains decoding software that recognizes bar code, magnetic stripe, or MICR information, decodes it, and transmits the information in a format that the host computer can use. In basic terms, the wedge allows a "dumb" input device (one without built-in decoding) and the host system to "talk" to one another.
Wedges also have several other functions aside from decoding and interfacing. Often, the wedge provides the proper power supply to the scanner or other input device. For example, standard RS-232 ports on most POS terminals are not designed to deliver the correct voltage for most scanners, nor can they decode the data from a nondecoded output device such as a wand, CCD, or other laser scanner.
Many wedges provide an additional RS-232 input port and magnetic stripe reader (MSR) port so users can quickly add a magnetic stripe reader, signature capture input, or another device such as a scale, as requirements change.
Which configuration? As you are probably aware, there are hundreds of different terminals and input devices. Wedges also come in several varieties, ranging from simple models with limited decoding capabilities, to more sophisticated versions with several types of interfaces and decoding options.
There are three basic ways a wedge can be used in a data collection system. Custom variations are common, but all are derived from these standard hardware configurations:
Keyboard Wedge
In this configuration, the wedge takes scanner and other input device information, decodes the data, and translates it into a TTL keyboard signal that the host system interprets as coming from the keyboard. There is often no need to modify the host system program to accept the data from the wedge since it appears to the system as if the data was entered on the keyboard (see figure 1). Some companies incorporate keyboard wedges into their scanners. These specialized scanners contain decoding electronics plus interface cabling. Portable computers do not usually offer a keyboard port through which the wedge can communicate. Software solutions are available to deal with this problem; the software program transfers data through the PCs communications port to the computer's keyboard buffer.
Direct Connection
The wedge decodes the data from an input device that transfers the information to an input port on the host device. The host device's interface may be serial RS-232 asynchronous data, or one of the proprietary POS formats such as IBM 46XX, NCR OCIA, or IBM/Fujitsu OCR (see figure 2).
RS-232 Serial Wedge
This configuration places the wedge between an asynchronous or serial terminal and the host computer. The wedge transmits the decoded information from an input device to a host computer; the host computer receives the data as if it originated at the asynchronous terminal (see figure 3).
An alternative to using a wedge for decoding is to deploy a scanner that has built-in decoding and interfacing capabilities. Depending on your particular system requirements, this can be an attractive option. For example, it saves on space and cabling. On the down side, your host computer or terminal may have only one RS-232 input, which will make it difficult to add other input devices in the future.
Written b y Thomas D. Britton, from Hand Held Products
 |
