LCD to a PC Parallel Port

Posted on Aug 15, 2012

The circuit is pretty simple. The data lines on the LCD match up well with the data lines of the parallel port, and extra parallel port I/O lines can be used to simulate the RS, R/W, and E signals on the LCD. The LCD module is pretty low-lower (with the exception of the backlight), so I found that it can be powered from most parallel ports. It worked fine with all the desktop PC's I tried it with, but a laptop I tried (a Toshiba something-or-other) just didn't have enough oomph to power the LCD

LCD to a PC Parallel Port
Click here to download the full size of the above Circuit.

The 10K pot controls the contrast of the LCD, though, in practice, I've found that it usually ends up at the ground rail, so you might be able to get by without the pot, and just tie VLC to ground. The diode from pin 17 of the printer port to pin 2 of the LCD simply blocks voltage from flowing back into the printer port (in case you hook up an external power supply). If you use an external supply, it's intended to connect to the place on the schematic labeled "+5V". This external supply can also be used to power the LCD's LED backlight (through a current-limiting resistor -- 100 ohms is probably too high, but it will turn the backlight on at least dimly). I built this circuit up on a little Radio Shack protoboard, using a DB25 for the printer port connector, and a 16-pin terminal strip for the LCD connector, with the interconnects on the back. Not pretty, but it works fine ...

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