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Driving An LCD From The Parallel Port

You build the module, then use the software to display messages of to program a thermometer/thermostat chip.

By Peter Crowcroft and Frank Crivelli

Click for larger image

You’ll find LCDs, or liquid crystal displays, in a huge variety of appliances, consumer electronics and so on. Usually driven by a microcontroller, they’ve become very popular over recent years for information transfer and instructions and (usually!) make complicated equipment easier to operate.

But how do you get the message you want onto the LCD screen? It’s not difficult, as this simple project shows.

Circuit description

The circuit (Fig.1) is quite straightforward. In fact, most of the "work" is undertaken by the large integrated circuit hidden under the black blob on the rear of the LCD module PC board.

All we have to do is provide that module with the appropriate ASCII codes and these come from your computer’s LPT1, or parallel, port.

The project could have been as simple as that but we’ve gone one step further and added a temperature control chip, the DS1620, which we can use to make a simple but effective thermostat/thermometer in conjunction with the LCD module. The remainder of the circuitry is mainly power supply – and even that is very simple.

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