There are several project to connect a standard LCD modul to the LPT port of a LinuX computer. I currently use lcd4linux. This software allows a wide range of configuration. A lot of different parameters can be displayed.

The opportunities, that a display of 20x4 characters is able to offer where to limited for me. So on may device (see beside) I provided the option, to switch the content of the display by five keys. Use your mouse cursor moving it over the keys on the picture to see how the display changes it's content. The keys are connected to the 5 status lines of the LPT port.

You may download the software to read the keys using the link on the left hand side below software. The program reads the keys status and returns the number of the pressed kay on stdout. A simple shell script may provide different actions in dependency of the returned value. One example may be the call of lcd4linux with different configuration files. I build in this code directly into lcd4linux.

I will not take any liabiliy for damages on your hardware!!

Circuit description

The circiut is quite simple. The pins 10, 11, 12, 13, 15 are the input status pins of a LPT port. Using a pull resistor of 4,7k they are connected to +5V. On pressing the key the pin is switch to ground. This level change is determind by the software.

Pin 17 provides (controled by a command line switch of the software) +5V. Attention! The LPT port is able to provide weak current only. Don't overload it!

©  Axel Ehnert / 2000-2004

Last modified: 02.03.2004