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A Low Cost AT Keyboard Translator

This Low-cost project takes the complex scan codes from a PC keyboard and spits out standard ACCII codes. It's just the shot for use with the BASIC stamp and PIC series of microcontrollers but has lots of other uses as well.

By Steve Carroll and Bob Nicol

The rapid progress of computer technology has resulted in many old, fully-functional IBM AT keyboards being thrown away in favour of newer, fancier ones. If you’ve ever wanted to connect one of those discarded keyboards to a project which accepts standard ASCII codes, this AT Keyboard Translator could be just what you’re looking for.

In operation, the device connects directly to any 101/104-key AT keyboard with a 5-pin DIN connector and converts the key scan-codes to standard ASCII "character" and "control" codes. It then outputs these codes in standard inverted asynchronous format at 300, 1200, 2400 or 9600 baud. The baud rate chosen depends on your "receiver" and is selected using a single jumper designated HDR2 on the PC board.

Click for larger image

The output data is compatible with the RS-232 serial port of many devices, allowing you to send text or control codes to your application. It’s just the shot for interfacing with microcontrollers such as the BASIC Stamp, Counterfeit and PIC series (in fact, the device was originally designed to do just that). There really is no easier way to connect over 60 switches to one pin of a Stamp1, Counterfeit Stamp1, Stamp2 or PIC chip (the non-ASCII keys are not used).

Of course, it’s not just limited for use with microcontrollers. It can also interface with other serial devices such as a serial printer (via a suitable RS232 driver interface) or LCD drivers. One of the photographs with this article shows the AT Keyboard Translator driving a 4-line alphanumeric LCD via an "LCD Serial Backpack" (designed by Scott Edwards Electronics).

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