Running an HD44780 Display off the ATmega on a Gertboard

There was a thread on the Raspberry Pi forums about running a 16×2 HD44780 based display off the ATmega chip on the Gertboard.  I normally use a shift register to run my display, so I wasn’t much help to them.  I decided to try and get it setup without the shift register to help out the folks having trouble.
Running an HD44780 Display off the ATmega on a Gertboard
So, this instructable will detail how to go about getting an HD44780 display running off the ATmega chip on the Raspberry Pi Gertboard.

Step 1: Ground an 5V

The first step is to connect the display to ground and 5V on the Gertboard.  Because you have to connect a pot to the contrast, I hooked up the Ground and 5V to my breadboard, and plugged the display into that.

Step 2: Contrast

Pin 3 on the display controls Contrast. It’s connected from Pin 3 to a 1k pot to ground.
The output from Pin 3 gets connected to one side of the pot, and ground to the middle leg of the pot.

Step 3: Register Select

Pin 4 is Register Select.  This is our first pin connected to the ATmega chip on the Gertboard.  I chose pin 8, which is marked as PB0, just because I could.
Running an HD44780 Display off the ATmega on a Gertboard data pins
I added some white lines in the picture to help clear up where each pin was, as it was hard to tell.

Step 4: Read/Write

Pin 5 is the Read/Write pin, which allows you to read data off the display, or write data to the display.  Reading data is not something you want to do with your Gertboard, because it’s 3V3 based, and the output of the display is 5V.  You’ll likely fry your board.  So this pin goes to ground.

About The Author

Ibrar Ayyub

I am an experienced technical writer holding a Master's degree in computer science from BZU Multan, Pakistan University. With a background spanning various industries, particularly in home automation and engineering, I have honed my skills in crafting clear and concise content. Proficient in leveraging infographics and diagrams, I strive to simplify complex concepts for readers. My strength lies in thorough research and presenting information in a structured and logical format.

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