RPLCD-i2c

A Python 2/3 Raspberry Pi Character LCD library for the Hitachi HD44780 controller, I²C only version. May work on other embedded boards with I²C bus.

Based on RPLCD library https://github.com/dbrgn/RPLCD

Tested with the 20x4 LCD MT-20S4A, Raspberry Pi model B and PCF8574AN I²C port expander.

Original GPIO based library tested with: - 20x4 LCD that is sold for example by adafruit.com or mikroshop.ch - 16x2 LCD from mikroshop.ch

Depends on python-smbus library. For getting smbus support in Python 3.x use instructions provided here:

http://procrastinative.ninja/2014/07/21/smbus-for-python34-on-raspberry/

http://jtecheng.com/?p=959

Wiring

For setting up I²C bus on Raspberry Pi see pinout here:

http://elinux.org/RPi_Low-level_peripherals

For enabling I²C bus on Device Tree enabled kernel see instructions here:

https://github.com/raspberrypi/firmware/blob/master/boot/overlays/README

Connecting PCF8574A (DIP16 package) to Raspberry Pi B Rev. 2

with address bits A0, A1, A2 set to 0

RPi signal	RPi B rev2 pin #	PCF8574 signal	PCF8574 pin #
+3.3v	1, 17	VCC	16
GND	6, 9, 14, 20, 25	GND	1, 2, 3, 8
SCL	5	SCL	14
SDA	3	SDA	15

Connecting LCD display to PCF8574A and Raspberry Pi

with contrast set to maximum (U0 connected to GND)

PCF8574 signal	PCF8574 pin #	LCD signal	LCD Pin #
GND	8	GND, U0	1, 3
P0	4	RS (A0)	4
P1	5	R/W	5
P2	6	E	6
P4	9	DB4	11
P5	10	DB5	12
P6	11	DB6	13
P7	12	DB7	14

Connect display pin 2 (VCC) to Raspberry Pi pin 2 (5v) OR to Raspberry Pi pin 1 (3.3v) depending on your display required supply voltage.

To activate display backlight connect LCD pin 15 (+LED) to 5 or 3.3v, connect LCD pin 16 (-LED) to GND directly or through a MOSFET (see schemacic below).

It is recommended to connect 0.1 uF ceramic bypass capacitor between VCC (16) and GND (8) pins of port expander.

Connection schematics

Without backlight control

With backlight control

Backlight control requires N-channel MOSFET with certain characteristics, i.e. BS170, 2N7000, 2N7002.

Installation

git clone https://github.com/zador-blood-stained/RPLCD-i2c.git
cd RPLCD-i2c
sudo python3 setup.py install
# and/or
sudo python setup.py install

I²C bus number

For Rasbberry Pi Model A, B Rev 2, B+ and Raspberry Pi 2 use bus number 1 For Raspberry Pi Model B Rev 1 use bus number 0

I²C device address

To check your port expander address use gpio i2cd command (alternatively sudo i2cdetect -y 0 or sudo i2cdetect -y 1 depending on bus number) Example output with one PCF8574A connected at address 0x38:

% sudo i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- 38 -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
%

or refer to datasheet for your port expander.

Features, Code examples & Usage

See original library documentation here: https://github.com/dbrgn/RPLCD

Testing

To test your 20x4 display, please run the test_20x4.py script and confirm/verify each step with the enter key. Make sure to set your bus number and address to the CharLCD constructor in test_20x4.py.

License

This code is licensed under the MIT license, see the LICENSE file or tldrlegal for more information.

The module RPLCD/enum.py is (c) 2004-2013 by Barry Warsaw. It was distributed as part of the flufl.enum package under the LGPL License version 3 or later.