Control a HD44780 LCD display via I2C with the Raspberry Pi

LCD character displays are a simple and a cost-effective way to display a text. Thanks to the HD44780 controller, the control of the modules has become very simple. However, one must occupy many GPIOs for it. An alternative is the I2C data bus, which means that only two GPIOs are used.

In this tutorial a 20×04 HD44780 character display is controlled using a I2C display adapter. A logic converter is used to adjusting the voltage level for the module without damaging GPIOs.

Accessories

In order to access an HD47780 display via I²C, I have used the following accessories:

• 20×04 or 16×02 Character HD44780 Display (US / UK)
• I2C Display Adapter (US / UK)
• I2C Logic Level Converter (US / UK)
• Breadboard
• Jumper wire

Setup

The Raspberry Pi GPIOs can not get more than 3.3V voltage, but there are some modules (like this display), which send and want to receive 5V signals. For this, a Logic Level Converter can be used, which has 2 sides. On one side those connections that are running on 3.3V are connected and on the other those with 5V. You can recognize this at different characteristics (LV – HV), as you see in the following picture:

The pins are then connected as follows:

Here is a schematic drawing:

Any ground pin can be taken. For the sake of clarity, I chose pin 20 instead of pin 6 on the schematic diagram.

This configuration is also usable with other modules which require signals with a higher voltage than 3.3V (in this case 5V) (real time clock, etc.).

Software

Before we can start, two I²C tools are needed, which we install:

sudo apt-get install python-smbus i2c-tools

Then we will release I2C (if you have already released it from previous tutorials, you can skip it):

sudo raspi-config

Under “Interfacing Options”> “I2C” we activate it. Now add the corresponding entries to the modules file:

sudo nano /etc/modules

These two lines are added to the end:

Afterwards it has to be restarted, so that all changes take effect.

sudo reboot

If you have already connected the display, you can now test whether it has been detected (if you have one of the first Raspberry Pi’s [Rev.1], you have to pass 0 instead of 1):

sudo i2cdetect -y 1

The output should look like this:

pi@raspberrypi ~ $ sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- 27 -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

If you see a number other than 27, you must change this in the lcddriver.py file (ADDRESS = 0x27).

Let’s start with the code:

mkdir hd44780 && cd hd44780
wget http://tutorials-raspberrypi.de/wp-content/uploads/scripts/hd44780_i2c.zip
unzip hd44780_i2c.zip

With the help of the two included scripts, the display can now be addressed. To do this, we open the Python console and enter the following code:

sudo python

The first parameter of the lcd_display_string is for the text and the second for the row. You do not have to change all lines at once, but you can not easily replace individual characters. For this, the entire text (with the character changed at the desired position) would have to be retransmitted.

The contrast of my I2C adapter was at the beginning very low. If nothing should be shown, test the wheel on the back and look obliquely on the display.

Code Reference: https://github.com/CaptainStouf/raspberry_lcd4x20_I2C