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Lennard Electronics Ltd

Driving an Hitachi 44780 based LCD module

Here are three solutions for controlling a 44780 based module with a Parallax BS2.

The solutions are, a standard parallel connection, a SIPO connection, or an I2C connection, the later two save pins on the micro, but increase software complexity.

Each program displays the message "Lennard Electronics" on the LCD.

Notes: I have used a 2 x 20 LCD. If you are using a 2 x 16 LCD, you will need to make a few minor changes to the code. Also, regarding the contrast pin (pin 3). The easiest thing to do, is to ground pin 3. Of course, you will not have control over contrast (you'll get full contrast), but it will get you started quicker. If you want contrast control, connect a 10k trimmer between pins 1 and 2, with the wiper going to pin 3.

SIPO solution:

I2C solution:

Notes: the resistors are needed. The outputs of all I2C devices are open drain, so the 10k resistors are needed as pull up resistors. As the Stamp has totem pole outputs, there is a slight chance that a bus short could occur when being used with I2C, so the two 220 ohm resistors limit the current if that were to happen (example, if the I2C device pulled SDA low when the Stamp was outputing a High.

Parallel Solution: