16×2 LCD Module Control Using Python

Once you’ve played with LEDs, switches and stepper motors the next natural step is 16×2 alphanumeric LCD modules. These modules are cheap (less than $10) and easy to interface to the Raspberry Pi. They have 16 connections but you only need to use 6 GPIO pins on your Pi.

Most of the 16×2 modules available are compatible with the Hitachi HD44780 LCD controller. This allows you to buy almost any device and be sure it is going to work in much the same way as any other. There are loads to choose from on eBay with different coloured backlights. The one I purchased had a blue backlight.

LCD Module Hardware

The pinout of the module is :

  1. Ground
  2. VCC (Usually +5V)
  3. Contrast adjustment (VO)
  4. Register Select (RS).
    RS=0: Command, RS=1: Data
  5. Read/Write (R/W).
    R/W=0: Write, R/W=1: Read
  6. Enable
  7. Bit 0 (Not required in 4-bit operation)
  8. Bit 1 (Not required in 4-bit operation)
  9. Bit 2 (Not required in 4-bit operation)
  10. Bit 3 (Not required in 4-bit operation)
  11. Bit 4
  12. Bit 5
  13. Bit 6
  14. Bit 7
  15. LED Backlight Anode (+)
  16. LED Backlight Cathode (-)

Usually the device requires 8 data lines to provide data to Bits 0-7. However the device can be set to a “4 bit” mode which allows you to send data in two chunks (or nibbles) of 4 bits. This is great as it reduces the number of GPIO connections you require when interfacing with your Pi.

Here is how I wired up my LCD :

LCD Pin Function Pi Function Pi Pin
01 GND GND P1-06
02 +5V +5V P1-02
03 Contrast GND P1-06
04 RS GPIO7 P1-26
05 RW GND P1-06
06 E GPIO8 P1-24
07 Data 0
08 Data 1
09 Data 2
10 Data 3
11 Data 4 GPIO25 P1-22
12 Data 5 GPIO24 P1-18
13 Data 6 GPIO23 P1-16
14 Data 7 GPIO18 P1-12
15 +5V via 560ohm
16 GND P1-06

NOTE : The RW pin allows the device to be be put into read or write mode. I wanted to send data to the device but did not want it to send data to the Pi so I tied this pin to ground. The Pi can not tolerate 5V inputs on its GPIO header. Tying RW to ground makes sure the device does not attempt to pull the data lines to 5V which would damage the Pi.

In order to control the contrast you can adjust the voltage presented to Pin 3. This must be between 0 and 5V. I tied this pin to ground.

Pin 15 provides 5V to the backlight LED. It wasn’t clear on my device if this could be connected direct to 5V so I played safe and placed a 560ohm resistor in line with this pin.

Wiring Checks

Here are some sanity checks before you power up your circuit for the first time :

  • Pin 1 (GND), 3 (Contrast), 5 (RW) and 16 (LED -) ( should be tied to ground.
  • Pin 2 should be tied to 5V. Pin 15 should have a resistor inline to 5V to protect the backlight.
  • Pin 7-10 are unconnected
  • Pin 11-14 are connected to GPIO pins on the Pi

Python

You can control a HD44780 style display using any programmming environment you like but my weapon of choice is Python. I use the RPi.GPIO library to provide access to the GPIO.

Here is my code :

#!/usr/bin/python
#
# HD44780 LCD Test Script for
# Raspberry Pi
#
# Author : Matt Hawkins
# Site   : http://www.raspberrypi-spy.co.uk
#
# Date   : 26/07/2012
#

# The wiring for the LCD is as follows:
# 1 : GND
# 2 : 5V
# 3 : Contrast (0-5V)*
# 4 : RS (Register Select)
# 5 : R/W (Read Write)       - GROUND THIS PIN
# 6 : Enable or Strobe
# 7 : Data Bit 0             - NOT USED
# 8 : Data Bit 1             - NOT USED
# 9 : Data Bit 2             - NOT USED
# 10: Data Bit 3             - NOT USED
# 11: Data Bit 4
# 12: Data Bit 5
# 13: Data Bit 6
# 14: Data Bit 7
# 15: LCD Backlight +5V**
# 16: LCD Backlight GND

#import
import RPi.GPIO as GPIO
import time

# Define GPIO to LCD mapping
LCD_RS = 7
LCD_E  = 8
LCD_D4 = 25
LCD_D5 = 24
LCD_D6 = 23
LCD_D7 = 18

# Define some device constants
LCD_WIDTH = 16    # Maximum characters per line
LCD_CHR = True
LCD_CMD = False

LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line 

# Timing constants
E_PULSE = 0.00005
E_DELAY = 0.00005

def main():
  # Main program block

  GPIO.setmode(GPIO.BCM)       # Use BCM GPIO numbers
  GPIO.setup(LCD_E, GPIO.OUT)  # E
  GPIO.setup(LCD_RS, GPIO.OUT) # RS
  GPIO.setup(LCD_D4, GPIO.OUT) # DB4
  GPIO.setup(LCD_D5, GPIO.OUT) # DB5
  GPIO.setup(LCD_D6, GPIO.OUT) # DB6
  GPIO.setup(LCD_D7, GPIO.OUT) # DB7

  # Initialise display
  lcd_init()

  # Send some test
  lcd_byte(LCD_LINE_1, LCD_CMD)
  lcd_string("Rasbperry Pi")
  lcd_byte(LCD_LINE_2, LCD_CMD)
  lcd_string("Model B")

  time.sleep(3) # 3 second delay

  # Send some text
  lcd_byte(LCD_LINE_1, LCD_CMD)
  lcd_string("Raspberrypi-spy")
  lcd_byte(LCD_LINE_2, LCD_CMD)
  lcd_string(".co.uk")

  time.sleep(20)

def lcd_init():
  # Initialise display
  lcd_byte(0x33,LCD_CMD)
  lcd_byte(0x32,LCD_CMD)
  lcd_byte(0x28,LCD_CMD)
  lcd_byte(0x0C,LCD_CMD)
  lcd_byte(0x06,LCD_CMD)
  lcd_byte(0x01,LCD_CMD)  

def lcd_string(message):
  # Send string to display

  message = message.ljust(LCD_WIDTH," ")  

  for i in range(LCD_WIDTH):
    lcd_byte(ord(message[i]),LCD_CHR)

def lcd_byte(bits, mode):
  # Send byte to data pins
  # bits = data
  # mode = True  for character
  #        False for command

  GPIO.output(LCD_RS, mode) # RS

  # High bits
  GPIO.output(LCD_D4, False)
  GPIO.output(LCD_D5, False)
  GPIO.output(LCD_D6, False)
  GPIO.output(LCD_D7, False)
  if bits&0x10==0x10:
    GPIO.output(LCD_D4, True)
  if bits&0x20==0x20:
    GPIO.output(LCD_D5, True)
  if bits&0x40==0x40:
    GPIO.output(LCD_D6, True)
  if bits&0x80==0x80:
    GPIO.output(LCD_D7, True)

  # Toggle 'Enable' pin
  time.sleep(E_DELAY)
  GPIO.output(LCD_E, True)
  time.sleep(E_PULSE)
  GPIO.output(LCD_E, False)
  time.sleep(E_DELAY)      

  # Low bits
  GPIO.output(LCD_D4, False)
  GPIO.output(LCD_D5, False)
  GPIO.output(LCD_D6, False)
  GPIO.output(LCD_D7, False)
  if bits&0x01==0x01:
    GPIO.output(LCD_D4, True)
  if bits&0x02==0x02:
    GPIO.output(LCD_D5, True)
  if bits&0x04==0x04:
    GPIO.output(LCD_D6, True)
  if bits&0x08==0x08:
    GPIO.output(LCD_D7, True)

  # Toggle 'Enable' pin
  time.sleep(E_DELAY)
  GPIO.output(LCD_E, True)
  time.sleep(E_PULSE)
  GPIO.output(LCD_E, False)
  time.sleep(E_DELAY)   

if __name__ == '__main__':
  main()

If you use this code the only thing you will need to change is the GPIO pin mapping depending on what pins you use on your Pi GPIO header. Here are some photos :

Additional Notes : RS is low when sending a command to the LCD and high when sending a character. RW is always low to ensure we only ever input data into the module. 8 bit bytes are sent 4 bits at a time. Top 4 bits first and the last 4 bits second. Delays are added between certain steps to ensure the module can react to the signal before it changes.

The code above was inspired by code submitted by ‘texy’ on the RaspberryPi.org forum. I changed the way the bytes are broken down to bits as this significantly increased the response time of the display.

This entry was posted in Hardware, Python, Tutorials & Help and tagged , , , , , . Bookmark the permalink.



43 Responses to 16×2 LCD Module Control Using Python

  1. dex says:

    Hi,
    your example works fine but i’m hving problems using 20×4 LCD – what do I need to change in the script to show all 4 lines?

    thanks, dex

    • Matt says:

      I haven’t got a 20×4 LCD so I can’t check this but try …

      Change LCD_WIDTH = 16 to LCD_WIDTH = 20

      Update the line addresses to :

      LCD_LINE_1 = 0x80 # LCD RAM address for the 1st line
      LCD_LINE_2 = 0xC0 # LCD RAM address for the 2nd line
      LCD_LINE_3 = 0x94 # LCD RAM address for the 3rd line
      LCD_LINE_4 = 0xD4 # LCD RAM address for the 4th line

  2. Andreas says:

    Hmm, am I misreading something or is there some confusion under
    “Here is how I wired up my LCD”
    you say you wire LCD pin 1 to +5V p1_02 – but the LCD pin 01 is GND right?

    So under “Here is how I wired up my LCD” the LCD pin 01 should actually be to GND (p1_06) and LCD pin 02 to +5V (p1_02)?

    And in the schematics and “Wiring Checks” you say connect pin 1 to GND.
    Am I just tired and misreading?
    Thanks for the tutorial, making my way through it now! Just wanted to ask you that :)

  3. Markus says:

    Very nice tutorial, but there is another slight mistake. Under “Here is how I wired up my LCD” you used GPIO 7 and 8 for RS and E, but in your python code you set RS to 26 and E to 24. I had to change these lines to get my LCD working.

    • Matt says:

      Thanks Markus. I’ve corrected it now. The example uses GPIO pins that make the breadboard diagram easier but this is different to my real test circuit. I got confused between the two!

  4. hi I’m getting stuck with this, i cant get any output from the screen. It’s lit but nothing when I run the code.
    1. I’m running 2.7 python
    2. I’m running Raspbian
    3. I’m running the RPi.GPIO-0.3.1a
    4. I’m running python-rpi.gpio_0.3.1a-1_armhf.deb
    5. And i’m pretty sure my wireing is correct.

  5. Milan says:

    Hi Matt.

    Thank you for this tutorial.

    I had a problem.
    When the python’s script has finished, display fills by 32 characters of “inverted P”.
    Here is video:
    http://youtu.be/mrIJaIcRGkE

    It caused probably by electomagnetic noise (long wires between Raspberry and display).
    http://www.astromik.org/raspi/dis-wired.jpg

    I solved this problem attaching resistor 150k between pins 2 and 6 on the display port.
    Here is a picture:
    http://www.astromik.org/raspi/dis-resistor.jpg

    Now is all OK.


    … excuse my english :-)

    • Matt says:

      I think this is because when the script finishes the RPi.GPIO library configures all the pins as inputs. This leaves the Enable pin floating. Adding a resistor pulls it high so the screen doesn’t reset. I might give this a try on my circuit.

  6. chris says:

    i wired my screen up the same as yours but its VERY dark.

    theres no colour to the screen (i.e blue) and the character blocks are barely visible.

    using a 3.3k resistor as i couldnt find a 5600ohm. only other ones i have are 10k, 430, 330 resistors

    • Matt says:

      The LED backlight resistor is 560 ohm not 5600 ohm. If you are using 3.3K then the LED isn’t getting enough current. Use a 430 instead and that should light up the screen a bit better.

  7. magik says:

    I have gotten everything wired up and double checked everything, though I only get squares all the way across the LCD screen. I re wired everything just to make sure it was done correctly, still the same issue.

    Any ideas?

    Side note: I am also a bit unsure on the need for the resistor, the LCD can operate between 2.7 to 5.5V. Is the resistors purpose to stop the LCD from pulling more than 5v?

    • magik says:

      All fixed, was connectivity issues with the squares showing up. Once I had fixed that problem I then started getting weird characters showing up. That was also fixed by setting up my locale settings OR by ignoring what the SSH client sent as a locale. Everything is working good now, nice tutorial! Bit confusing in parts though.

    • Matt says:

      The resistor is for the LED backlight not the LCD itself. It usually isn’t clear but some LCD modules do not include a resistor to limit the current drawn by the LED backlight. So I always put one in to be sure.

  8. Matt says:

    Thanks for the great tutorial.

    I’ve tried this and have a worrying problem. I don’t see any text, just black squares accross the lower line of the display. What concerns me is that the data lines each read 5v when I run the Python script.

    Pin 5 is *definitely* grounded, and since the Pi should only ouput 3.3v on these pins I’m guessing this must mean a fault in the LCD?

    Any suggestions would be greatly appreciated.

    Many thanks,

    Matt

  9. MattCG says:

    Unhelpfully I’ve signed the above comment “Matt”. Apologies!

  10. Sagar says:

    I wired up exactly as seen in the diagram and ran the script. BUT lcd shows nothing. I checked my wiring and even program 2-3 times bit nothing helped.

    What do you think, what’s the problem??
    (This is my first gpio program.)

  11. Danilo says:

    Nice tutorial. In case someone’s looking for a full library for the HD44780 on the Raspberry Pi, here’s my attempt at doing so: https://github.com/dbrgn/RPLCD It’s tested both on 20×4 and 16×2 LCDs and provides test scripts to verify your wiring.

  12. Pingback: Afficheur LCD sur Raspberry Pi | Anderson69s

  13. Pingback: 16×2 LCD Modülünü Bağladık! - Raspberry Pi Türkiye Topluluğu

  14. GEORGE STUARTstuartgeordies says:

    Hello,
    I have just started with python and have a problem with the code.
    I am getting a invalid syntax error on a simple instruction.-
    lcd_string(“Raspberry Pi”) in the 16×2 LCD Module Control
    Where have I went wrong. thank you..

  15. Sam says:

    Hey, i was wandering: can i use a 330R resistor instead of the 630ohm?? If not can i use any of the following: 10k 1k0? Please reply ASAP! Thanks in advance and AMAZING tutorial!! (i had trouble following the table as there is no pin 6 and i couldn’t understand why so many things were on pin 6)!

    • Matt says:

      The resistor just limits current to the backlight LED. You could definitely use 1K0. 330 would be ok as well although that really depends on the exact specification of your module. Some modules have built in resistors. I would go for the 1K0 and see how bright the backlight is. If it is too dim then try the 330. Assuming the LED has 2V across it that would leave 3V across the resistor (5V-2V). 330ohm would mean the current is 9mA (3/330). That should be OK for most LEDs.

  16. Seb says:

    Hi,

    i want to show custom characters on the LCD. You think you can extend the tutorial for this? Would be great.

  17. Baaltazarian says:

    How to increase contrast, because my screen is very dark and text is nearly impossible to read?
    Photos:
    https://www.dropbox.com/s/eumkc827c9uai1m/20140727_121500.jpg
    https://www.dropbox.com/s/vt2ulhqkmiou2wt/20140727_121505.jpg

  18. mrsoltys says:

    Thank you so much for this! Very Helpful! Can you give any info as to why you skipped some pins? Also, any idea how to hook up and use an OLED display? SPI or I2C?

    • Matt says:

      Pins 7-10 aren’t required as the device supports sending the data in blocks of 4 bits. This makes the code a bit more complicated but saves bothering with those pins in hardware.

  19. Terry Horsnell says:

    Thanks very much for this code, however, I’m slightly mystified. I havent implemented it yet, just trying to understand what it does, and the routine ldc_init() is my problem. It apparently sends bytes 0x33, 0x32, 0x28, 0x0C, 0x06 and 0x01 to the device in pairs of nibbles, but looking at the Hitachi HD44780U datasheet (Table 12, page 42), because the device powers up in 8-bit mode, the first nibble it gets will be interpreted as a byte, and so it will not need a second nibble in this instance. Its only when it has been put into 4-bit mode by this first nibble that it needs subsequent data in pairs of nibbles. So how come it doesnt get all out of sync…
    Could you expand on what goes on in lcd_init() please?

    Cheers,
    Terry

    • Lloyd says:

      lcd_byte(&H33, LCD_CMD)
      #synhcro nibbles (puts it in 8 bit mode twice — 00110011, as is written as 0011XXXX 0011XXXX)
      lcd_byte(&H32, LCD_CMD)
      #whilst still in 8 bit mode, 2nd part puts it in 4 bit mode. 00110010 (as treats 0010 as 2nd cmd)
      #at this point it is “Synched” (as nibbles can and do get out of sync elsewise)
      lcd_byte(&H28, LCD_CMD)
      #whilst keeping it in 4 bit mode (0010XXXX), the latter (1000 in 00101000) says it is 2 line device.
      lcd_byte(&HC, LCD_CMD) #set display on
      lcd_byte(&H6, LCD_CMD) #set moving direction of cursor
      lcd_byte(&H1, LCD_CMD) #Clear — takes 2ms.

  20. Marcos says:

    If any of you guys is having problems with the contrast try using a potentiometer from the contrast pin to the ground. (Y)

  21. Kirk says:

    Hi Matt – Great tutorial – Its the clearest one on the Web that I have come across. I was wondering do you have an example where I could use the same specification display in 8bit mode? Many thanks in advance!

  22. Mir Turk says:

    Hello,

    Thanks for publish this tutorial but I’ve questions.

    I wired other modul on my Raspberry Pi so I can not use GPIO25 and GPIO 08. Can I use other pinouts instead of this pinouts to work both other modul and LCD together?

    Thanks.

  23. Pedro Rodrigues says:

    Hi.
    I have 20×4 lcd module lcm1602 with hd44780. I’m using I2c.

    Do you have sample code for using that with I2c on Raspberry Pi B+ ?
    I want do scrolling (up, down, left , right) and custom character.

    I’m using I2C with Raspberry Pi B+ connected to (SDA, SCL, GND, VCC).
    Is working, but i’m newbie and i’m interested in do more things like i said with it.

    Thanks

  24. Christian says:

    Hi,

    Your Python script is great! Thanks a lot!

    Is it difficult to modify it in a way that the LCD is used in 8-bit mode?

    I ask because I don’t need the other GPIOs and maybe when the LCD is used in 8-bit mode, lesser CPU cycles are wasted.

    Best Regards
    Christian

  25. Stephen(Newbie) says:

    Hello, just a newbie here..
    At first, I tried everything just like what was instructed..
    wired them in order: pins 1-16.. ran the code, then nothing appeared, only a (blue) LED background on the screen. http://imgur.com/aACM17Y.jpg

    So I checked for the pin config on the module (there’s no datasheet), and found this: http://i.imgur.com/75gCeko.jpg

    so I rewired it according to what was labelled, it did not work; no display. I exchanged the pins 15 and 16 (which is reversed now because of the “label” at the back) and the LED background lit up again this time with white squares.. http://imgur.com/Rpnmz84.jpg

    I thought it was fine.. then when I ran the program, nothing appears, no error displayed on the terminal also. What seems to be the problem? Maybe the data pins are jumbled? -.-

    Anybody help please? :(

    PS. The model written at the back is jm1602m (searched for the pin config on the net but it says same with your example above)

    • Matt says:

      Have you connected anything to Pins 7-10?

      • Stephen(Newbie) says:

        The back of the lcd pins were written: 15,16,1————14 but it doesn’t even light the LED backlight but if I exchange the pins 15 and 16, it does and now with white squares. so I’m using 16,15,1————14. If that is the correct pin assignment, then no, I left pins 7-10 unconnected.

  26. Ricky says:

    Hello! Can you explain the code further please? The comments in the code were useful but I want to fully understand it. I am planning to interface the lcd with inputs on my keyboard but don’t know how.. Or can you link me to a helpful guide to lcd codes?

    Best regards

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