“Sophisticated” RFID chip readers or barcode readers are shipped with drivers, libraries, or special apps which provide methods for routing the output of the reader to a specific target. If, for example, the information of the RFID tags or barcodes should simply go to a file, this kind of readers provide ways to define the location and format of that file.

Many “cheaper” readers, however, simply act as a USB keyboard. If they recognize an RFID tag (or barcode) these readers simulate keystrokes that represent the resulting code. Consequently, the code will always be sent to the active window. This is fine for many applications, as long as the desired window is always in the foreground and has the keyboard simulator focus. It does make some trouble, however, if you want to do things in parallel to receiving RFID codes / barcodes.

这里概述不同的概念为capturing and re-routing the keyboard simulator events from these devices. If you have already bought one of these “keyboard-like” RFID readers (or barcode readers), you do not need any additional hardware as this tutorial will highlight different software-based ways how to route their output to an application that does not currently have the keyboard focus.

As a small scenario, let’s consider the following: The RFID reader is connected to a PC that hosts an Access database. Every time, someone is presenting his RFID tag to the reader, it should send the corresponding tag number to the database. It is easy to achieve this by creating a corresponding input form. The reader will simulate keystrokes including the enter key, so each time these keystrokes reach the input form, it will create a new dataset. Technically, however, the keystrokes simply always go to the foreground window, so you cannot work on anything else like editing a text document with the “real” keyboard. Activating the window with this text document would route all keyboard events here: that window would receive the events from all keyboards including the RFID/barcode reader now - even if you move that window to another screen as in the example sketch above.

According to a large number of posts in newsgroups and on Q&A websites, a many people have come across the same problem and tried to capture the keystrokes from the RFID or barcode readers - with more or less success. Their common goal is to prevent the key sequences from going to the window that has the keyboard focus, and to send the information to some other target, i.e. a different running application, a file, a server, or a database. They discussed many different approaches of which some work well and others do not really work at all. The table given above shows a summary of some of these concepts. Some solutions are based on pure software, some require additional hardware. only. As most discussions were about a solution for Windows, the subsequent sections will mainly address this operating system while mentioning Linux concepts, too.