Lcd display

[Lucifer]

I have a 16x2 LCD display (a bit like the one from adafruit) with i2c and I can get it to display messages I input into the python code and then run. I was wondering if anyone had created a piece of python code that would allow me to type a message and have it instantly displayed on the display.

[DirkS]

Does http://www.raspberrypi-spy.co.uk/2015/0 ... pberry-pi/ help?

[Lucifer]

No, I want to display everything I type on the LCD. type a message and have it instantly displayed on the display.

[DougieLawson]

Try this program to check whether your 16x2 LCD is working and wired correctly.

Code: Select all

#!/usr/bin/python
import smbus
import time

I2C_ADDR  = 0x27 # I2C device address
LCD_WIDTH = 16   # Maximum characters per line

LCD_CHR = 1 # Mode - Sending data
LCD_CMD = 0 # Mode - Sending command

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

LCD_BACKLIGHT  = 0x08  # On

ENABLE = 0b00000100 # Enable bit

E_PULSE = 0.0005
E_DELAY = 0.0005

bus = smbus.SMBus(1) # Rev 2 Pi uses 1

def lcd_init():
  lcd_byte(0x33,LCD_CMD) # 110011 Initialise
  lcd_byte(0x32,LCD_CMD) # 110010 Initialise
  lcd_byte(0x06,LCD_CMD) # 000110 Cursor move direction
  lcd_byte(0x0C,LCD_CMD) # 001100 Display On,Cursor Off, Blink Off
  lcd_byte(0x28,LCD_CMD) # 101000 Data length, number of lines, font size
  lcd_byte(0x01,LCD_CMD) # 000001 Clear display
  time.sleep(E_DELAY)

def lcd_byte(bits, mode):
  bits_high = mode | (bits & 0xF0) | LCD_BACKLIGHT
  bits_low = mode | ((bits<<4) & 0xF0) | LCD_BACKLIGHT
  print '{0:8b}'.format(bits_high)
  bus.write_byte(I2C_ADDR, bits_high)
  lcd_toggle_enable(bits_high)
  print '{0:8b}'.format(bits_low)
  bus.write_byte(I2C_ADDR, bits_low)
  lcd_toggle_enable(bits_low)

def lcd_toggle_enable(bits):
  time.sleep(E_DELAY)
  bus.write_byte(I2C_ADDR, (bits | ENABLE))
  time.sleep(E_PULSE)
  bus.write_byte(I2C_ADDR,(bits & ~ENABLE))
  time.sleep(E_DELAY)

def lcd_string(message,line):
  message = message.ljust(LCD_WIDTH," ")
  lcd_byte(line, LCD_CMD)
  for i in range(LCD_WIDTH):
    lcd_byte(ord(message[i]),LCD_CHR)

def main():
  lcd_init()
  while True:

    lcd_string("Line1 ---16CHARS",LCD_LINE_1)
    lcd_string("I2C LCD         ",LCD_LINE_2)

    time.sleep(3)

    # Send some more text
    lcd_string(">         Line1 ",LCD_LINE_1)
    lcd_string(">        I2C LCD",LCD_LINE_2)

    time.sleep(3)

if __name__ == '__main__':

  try:
    main()
  except KeyboardInterrupt:
    pass
  finally:
    lcd_byte(0x01, LCD_CMD)

You should be able to modify that program to accept input and display it on your LCD.

[RDS]

Try this program to check whether your 16x2 LCD is working and wired correctly ...

Dougie, I know you posted it a few months ago but I cannot get this program to work on Python 3, or is it a Python 2 program?

[scotty101]

Looks like python2 given the missing parenthesis for print

Code: Select all

print '{0:8b}'.format(bits_high)

[RDS]

Looks like python2 given the missing parenthesis for print.

Yes that is what I thought but I have added those and still cannot get it to work. Having said that though, I have a 20 x 4 LCD so that could now be why. Just wanted to eliminate one thing at a time. Thanks.

[scotty101]

Any other error messages?

Does i2cdetect find the display?

[RDS]

@scotty101
Thank you for your reply.

Yes, sudo i2cdetect -y 1, does detect the display and outputs the following:

Code: Select all

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

When I run the program in Python 2, it gives the following output, so it seems to run so far (by printing 111000 and then 1000) before reporting errors

Code: Select all

  111000
    1000

Traceback (most recent call last):
  File "/home/pi/I2C Python 2 program.py", line 79, in <module>
    lcd_byte(0x01, LCD_CMD)
  File "/home/pi/I2C Python 2 program.py", line 38, in lcd_byte
    bus.write_byte(I2C_ADDR, bits_high)
IOError: [Errno 5] Input/output error

[scotty101]

Does running the script with 'sudo python your_script.py' make any difference.

[RDS]

@scotty101,
I am not familiar with that program. Is it something I need to download from somewhere.

[scotty101]

No..

It is standard. It is a command that elevates the permissions of your program.

[DougieLawson]

You need a quick tweak to my sample python2 program
Change

Code: Select all

I2C_ADDR  = 0x27 # I2C device address

to

Code: Select all

I2C_ADDR  = 0x3F # I2C device address

[RDS]

You need a quick tweak to my sample python2 program

Thank you. That has made a difference but although there are now no errors, it has just produced a (seemingly) never ending list of binary? on the screen but nothing on the LCD. The following is just a small sample and it was continuing until I pressed CTRL-C.

I was expecting an output as indicated in the last few lines of your program.

Have I done something wrong?

Code: Select all

  111000
  111000
  111000
  101000
    1000
 1101000
    1000
11001000
  101000
10001000
    1000
   11000
10001000

[DougieLawson]

That stuff is just some debugging to show the bits that are being sent to the LCD.

The more important test involves a pair of MK I eyeballs and the LCD you're trying to drive.

[RDS]

The more important test involves a pair of MK I eyeballs and the LCD you're trying to drive.

Ha Ha,
Yes I had those but a simple adjustment of the pot on the back of the I2C unit has enabled the screen to go from completely blank to displaying the necessary lines!
Thank you.