Drive a 16×2 LCD with the Raspberry Pi

Overview

Adding a LCD to any project immediately kicks it up a notch. This tutorial explains how to connect a inexpensive HDD44780 compatible LCD to the raspberry pi using 6 GPIOs. While there are other ways to connect using I2C or the UART this is the most direct method that get right down to the bare metal.
Drive a 16x2 LCD with the Raspberry Pi
This technique:

  • allows for inexpensive LCDs to be used
  • does not require any i2c drivers
  • won’t steal the only serial port on the Pi.

The example python code sends date, time and the ip address to the display. If you are running a Pi in headless mode being able to determine the IP address at a glance is really handy.

To Follow This Tutorial You Will Need

Wiring the Cobbler to the LCD

The LCD

Whenever you come across a LCD that looks like it has 16 connectors it is most likely using a HD44780 controller. These devices provide the same pinouts making them relatively easy to work with. The LCD uses a parallel interface meaning that we will need many pins from our raspberry pi to control it. In this tutorial we will use 4 data pins (4-bit mode) and two control pins.The data pins are straight forward. They are sending data to the display (toggled high/low). We will only be using write mode and not reading any data.

The register select pin has two uses. When pulled low it can send commands to the LCD (like position to move to, or clear the screen). This is referred to as writing to the instruction or command register. When toggled the other way (1) the register select pin goes into a data mode and will be used to send data to the screen.

The read/write pin will be pulled low (write only) as we only want to write to the LCD based on this setup.

The enable pin will be toggled to write data to the registers.

LCD Pinout

  1. Ground
  2. VCC – 5v not 3.3v
  3. Contrast adjustment (VO) from potentiometer
  4. Register Select (RS). RS=0: Command, RS=1: Data
  5. Read/Write (R/W). R/W=0: Write, R/W=1: Read (we won’t use this pin)
  6. Clock (Enable). Falling edge triggered
  7. Bit 0 (Not used in 4-bit operation)
  8. Bit 1 (Not used in 4-bit operation)
  9. Bit 2 (Not used in 4-bit operation)
  10. Bit 3 (Not used in 4-bit operation)
  11. Bit 4
  12. Bit 5
  13. Bit 6
  14. Bit 7
  15. Backlight LED Anode (+)
  16. Backlight LED Cathode (-)

Before wiring, check that your LCD has an LED backlight, not an EL backlight. LED backlights use 10-40mA of power, EL backlights use 200+ma! EL backlights are often cheap to get but are not usable, make sure you don’t use one or you will overload the Pi. Some cheap LCDs that have LED backlights do not include a resistor on the LCD module for the backlight, if you’re not sure, connect a 1Kohm resistor between pin 15 and 5V instead of connecting directly. All Adafruit LCDs have LED backlights with built in resistors so you do not need an extra resistor!

Wiring Diagram

First, connect the cobber power pins to the breadboard power rail. +5.0V from the cobbler goes to the red striped rail (red wire) and GND from the cobbler goes to the blue striped rail (black wire)

In order to send data to the LCD we are going to wire  it up as follows

  • Pin #1 of the LCD goes to ground (black wire)
  • Pin #2 of the LCD goes to +5V (red wire)
  • Pin #3 (Vo) connects to the middle of the potentiometer (orange wire)
  • Pin #4 (RS) connects to the Cobber #25 (yellow wire)
  • Pin #5 (RW) goes to ground (black wire)
  • Pin #6 (EN) connects to cobber #24 (green wire)
  • Skip LCD Pins #7, #8, #9 and #10
  • Pin #11 (D4) connects to cobber #23 (blue wire)
  • Pin #12 (D5) connects to cobber #17 (violet wire)
  • Pin #13 (D6) connects to cobber #21 (gray wire)
  • Pin #14 (D7) connects to cobber #22 (white wire)
  • Pin #15 (LED +) goes to +5V (red wire)
  • Pin #16 (LED -) goes to ground (black wire)

Then connect up the potentiometer, the left pin connects to ground (black wire) and the right pin connects to +5V (red wire)

Schematic

5v LCD vs 3.3v Pi

The raspberry Pi GPIOs are designed for 3.3v, but our LCD is a 5v device. It’s fine to use a 5v display, but only if we are sending data out of the Pi. We are not going to use the 3.3v power rail on the cobbler and we will tie the RW (read/write) pin of the display to GND as we do not want the display sending sending a 5v signal into the Pi.Don’t cross the streams!

Preparing the LCD

Before you start, make sure you have a strip of 0.1″ male header and a 10K potentiometer. All Adafruit Character LCDs come with these parts so you should be good to go.

Most LCDs have a strip of 16 pins on the top, if the header is a little longer, just break it off until its the right length
Next you’ll need to solder the header to the LCD.You must do this, it is not OK to just try to ‘press fit’ the LCD!
Start by connecting the 5V and GND wires from the cobbler to the breadboard. Then connect pins #1, #2 and #15, #16 to the breadboard power rails as shown. The backlight should come on. If it doesn’t, check the wiring!

Next, wire up the contrast potentiometer as shown above, with the middle pin connecting to LCD pin #3 and the other two pins going to 5V and ground.Twist the potentiometer until you see the first line of the LCD fill with boxes. If you don’t see the boxes, check your wiring!

Finish the wiring for the RS, RW, EN, D4, D5, D6, and D7 pins as shown in the diagram up top
That’s it! Now you’re ready to run the python script to draw text on the screen!

Necessary Packages

This guide is based on Debian’s “Wheezy” release for Raspberry Pi. It was made available in Mid July 2012. The following items must be installed in order to utilize the Raspberry Pi’s GPIO pins. If you are running Adafruit’s Occidentalis you can just skip this page.

Add the latest dev packages for Python (2.x)

Python Script

Drive a 16x2 LCD with the Raspberry Pi Schemetic

NOTE: This page describes an older version of the Raspberry Pi character LCD Python code. You can find a newer library that works on more platforms like the Raspberry Pi and BeagleBone Black by checking out the new character LCD Python library guide. For new projects it’s recommended to use the new library!

The Code

# SPDX-FileCopyrightText: 2018 Mikey Sklar for Adafruit Industries
#
# SPDX-License-Identifier: MIT

from subprocess import Popen, PIPE
from time import sleep
from datetime import datetime
import board
import digitalio
import adafruit_character_lcd.character_lcd as characterlcd

# Modify this if you have a different sized character LCD
lcd_columns = 16
lcd_rows = 2

# compatible with all versions of RPI as of Jan. 2019
# v1 - v3B+
lcd_rs = digitalio.DigitalInOut(board.D22)
lcd_en = digitalio.DigitalInOut(board.D17)
lcd_d4 = digitalio.DigitalInOut(board.D25)
lcd_d5 = digitalio.DigitalInOut(board.D24)
lcd_d6 = digitalio.DigitalInOut(board.D23)
lcd_d7 = digitalio.DigitalInOut(board.D18)


# Initialise the lcd class
lcd = characterlcd.Character_LCD_Mono(lcd_rs, lcd_en, lcd_d4, lcd_d5, lcd_d6,
                                      lcd_d7, lcd_columns, lcd_rows)

# looking for an active Ethernet or WiFi device
def find_interface():
    find_device = "ip addr show"
    interface_parse = run_cmd(find_device)
    for line in interface_parse.splitlines():
        if "state UP" in line:
            dev_name = line.split(':')[1]
    return dev_name

# find an active IP on the first LIVE network device
def parse_ip():
    find_ip = "ip addr show %s" % interface
    find_ip = "ip addr show %s" % interface
    ip_parse = run_cmd(find_ip)
    for line in ip_parse.splitlines():
        if "inet " in line:
            ip = line.split(' ')[5]
            ip = ip.split('/')[0]
    return ip

# run unix shell command, return as ASCII
def run_cmd(cmd):
    p = Popen(cmd, shell=True, stdout=PIPE)
    output = p.communicate()[0]
    return output.decode('ascii')

# wipe LCD screen before we start
lcd.clear()

# before we start the main loop - detect active network device and ip address
sleep(2)
interface = find_interface()
ip_address = parse_ip()

while True:

    # date and time
    lcd_line_1 = datetime.now().strftime('%b %d  %H:%M:%S\n')

    # current ip address
    lcd_line_2 = "IP " + ip_address

    # combine both lines into one update to the display
    lcd.message = lcd_line_1 + lcd_line_2

    sleep(2)

Download the Code

Let’s put this file right in your home directory for simplicity. The wget command makes things easy.

$ wget https://raw.githubusercontent.com/adafruit/Adafruit_Learning_System_Guides/master/Drive_a_16x2_LCD_with_the_Raspberry_Pi/Drive_a_16x2_LCD_with_the_Raspberry_Pi.py

Running the Code

The following command will start the program and you should see the LCD display come to life with date, time and IP address.

$ sudo python3 ./Drive_a_16x2_LCD_with_the_Raspberry_Pi.py

It’s all fine and dandy to have a script which we can manually run, but wouldn’t it be nice to have the time and ip address pop up on the display when the Raspberry Pi boots up? This is done using an init script which runs our Python code every time your Raspberry Pi boots up.

Download the service file

The following command will allow you to download the lcd.service file directly to your Pi.

$ wget https://raw.githubusercontent.com/adafruit/Adafruit_Learning_System_Guides/master/Drive_a_16x2_LCD_with_the_Raspberry_Pi/lcd.service
[Unit]
Description=LCD date|time|ip
Requires=network-online.target
After=network-online.target

[Service]
ExecStart=/usr/bin/python3 Drive_a_16x2_LCD_with_the_Raspberry_Pi.py
WorkingDirectory=/home/pi
StandardOutput=inherit
StandardError=inherit
Restart=always
User=pi

[Install]
WantedBy=network-online.target

Place the lcd.service file

The lcd.service file needs to be copied into the correct location and the systemctl command can be used to start | stop | enable the service. It is a good idea to test this before enabling as there might be a minor path difference on your system.

$ sudo cp lcd.service /etc/systemd/system

Test the lcd.service

$ sudo systemctl daemon-reload
$ sudo systemctl start lcd.service
$ ps auxww | grep -i 16x2
learn_raspberry_pi_ps-rpi-screenshot.png

The following commands read the updates to the service file, start the lcd.service and confirm that the process is running. If the script shows up in the ‘ps’ command output you have done everything correctly and can now enable the service and reboot. The service should activate upon bootup automatically.

Enable lcd.service

$ sudo systemctl enable lcd.service

Now on each boot the LCD will automatically show the date/time/ip address on startup. This means you will know when the Pi is reachable and what the ip address is without having to plug a monitor in.

Last, but not least: My Pi came configured with UT (Universal Time). I prefer to see time based on my time zone, which is Mountain. Here is how to configure time on the Pi for any location. This is a one time configuration setting that will survive between reboots.

We can use raspi-config to easy set our timezone. Choose the following:

  • Localisation Options
  • Change Timezone
  • Continent / Country
  • Time zone

Run raspi-config

$ sudo raspi-config
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