What am i doing wrong with my hd44780 16x2 lcd?

Boz

i2c does indeed seem to be a bit of a mess, just so I understand this correctly I currently have the lcd connected like this:

GND - pin 6
VCC - pin 4
SDA - pin 3
SCL - pin 5

I followed this diagram:
0_1500658168505_68747470733a2f2f692e696d6775722e636f6d2f575450487a73662e706e67.png

Pin 4 shows 5v so if my backpack is TTL (5v) how does this pose a problem?

PS: Thanks for both of your help btw it's much appreciated.

Boz

@cyperghost I have a spare hd44780 with no backpack to wire up directly if need be, but I'm concerned I won't have room for a breadboard so I was trying to stay away from that if possible.

future.child

@boz The pi can output 5V as well as 3v3 but the gpio ports are only 3v3 tolerant, therefore you need a level shifter. The 5V produced by the backpack is simply to high and possibly could damage the ports.

Boz

Ok i'll disconnect the lcd for now until I get the level shifter (will be next week now).
Is this one ok?
https://shop.pimoroni.com/products/sparkfun-logic-level-converter-bi-directional?utm_medium=cpc&utm_source=googlepla&variant=7493045377&gclid=CjwKCAjwzMbLBRBzEiwAfFz4gQd35zRrMF0RFk7mjybTQZZHGF0hfcEVPTglsuBgr-SAGlMsuHTdDBoCKX0QAvD_BwE

future.child

@boz Yes that one would do fine.

cyperghost

@Boz
No No! Please don't directly wire 5V to SDA/SCL! This will damage the Input GPIO! You rather should use Pin 1 for power... with much much luck it works!

If you prefer easy wiring then use a I2S designed for RPi with 3,3V TTL but most LCDs need at least 5V.

Annother method could this one
You power it up with 5V to ground and the PIC "could" interpret 3,3V signals from UART of Pi.... I said "could". Usually the signal of high is 2,5-2,7V to 3,3V could work!

What the difference between the UART and the I2C? The UART is a one way communication so no signal reaches the Pi and so overvoltage is no risk!

The cleanest way imho is the direct wiring! The Breadboard is just for testing. If it works you can solder it directly

cyperghost

@future-child said in What am i doing wrong with my hd44780 16x2 lcd?:

@boz The pi can output 5V as well as 3v3 but the gpio ports are only 3v3 tolerant, therefore you need a level shifter. The 5V produced by the backpack is simply to high and possibly could damage the ports.

right!

Boz

@cyperghost So there is already a chance that the SDA/SCL pin is damaged? If so would it have damaged the Dac+light or the pi itself?
I'm grateful that people write tutorials such as the one I followed for the display but there seems to be a lot of conflicting information out there.
So i can either go with the level shifter or the direct wiring without the backpack, I'm gonna read back through your posts and see what pins need to be connected to directly wire this.
Hopefully there has been no damage and i can carry on with my troubleshooting or better still the damn thing just works lol!

cyperghost

Well I have an I2S backpack here, without LCD and I can detect it with i2cdetect -y 1 on 27h.
Try to wire the whole thing on 3,3V and take a look to the red LED. Then check with i2cdetect -y 1

There are tons of "how to" connect a HD44780 on google, the poti isn't needed - it's for contrast setting

EDIT: Easier setup without resistors! This one is for Pi B, but the GPIOs are backwards compatible. This graphic is only for example! How a wiring should work! I've tested it for several years and it worked so far!

Boz

So i just swap pin 4 for pin 1?

Boz

I feel which ever method i choose i should remove the dac and connect directly to the pi. Even though the lcd was connected without a level shifter it still had power...so the reason why i get no address from i2cdetect -y 1 must be because either the gpio input was damaged or the header on the dac isn't soldered very well.
Removing the dac narrows it down i reckon.

cyperghost

@boz said in What am i doing wrong with my hd44780 16x2 lcd?:

So i just swap pin 4 for pin 1?

Yes this will not overvoltage SDL/SDA ... If the red LED is on then the backpack could work and may be detected. With much much luck your display will also run!

With this config my I2S device results this

pi@raspberrypi:~ $ 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: -- -- -- -- -- -- -- --

Boz

Ha ha we'll see!

Boz

Tried with 3.3v pin, backpack gets power but still no address. Will try this again over the weekend but connected directly to the pi.

cyperghost

@Boz Maybe you remove your I2S devices, too and look to the posting @future-child gave you. This is a nice instruction as well

Boz

Thanks, I'll spend some time fault finding/process of elimination. I'll try all the things you guy's have suggested and see how i get on.

Boz

Success!!
I dug out an old rpi2 and tried the display on that using i2c (3.3v). I got an address from i2cdetect -y 1.... (3f) and changed a few test scripts to suit all of which worked.
I want on to change the script I was going to use in my build (retropie_clcd.py) and then altered all the text to what I wanted.
Tried everything that I'd just done exactly the same on my rpi3 with dac etc and still no address. So it has to be the dac for whatever reason, I'll connect the lcd directly to the rpi3 with no dac attached see if that works.

cyperghost

@Boz - Don't give up!
I was in luck, on my work we used former HD44780 display for giving text messages to consumer, so I soldered my I2S-backbag to this and it works like a charm. Anyway the characters don't look good

Hello RetroPie!
Greetings from
  cyperghost
  & crcerror

It's an 16x4 display and it worked fine with level shifter!

Boz

No I won't give up, I used the sd card from the rpi2 (where the lcd was working) and stuck it in the rpi3 with no dac attached and bingo!!
So now I'm going to reconnect the dac and try that. If that works also I know it's not a hardware issue :)
I'll start with a fresh image then add the ATXraspi and test lcd, add the DAC then test lcd.....and so on until either I find out the problem or it just works (and I never find out what the problem was)
Level shifter getting delivered this week hopefully.

cyperghost

@Boz
I used the python libary posted here - it worked flawless with my setup. Keep care of upper and lower cases. Just use the same filenames as posted in the thread.

Good luck mate

EDIT:

Just for conserving (INTERNET IS FLUID!)
Testing python sniplet retropie.py

import I2C_LCD_driver
from time import *

mylcd = I2C_LCD_driver.lcd()

mylcd.lcd_display_string("Hello RetroPie!", 1)
mylcd.lcd_display_string("Column 3!", 2, 3)

LCD driverlibary I2C_LCD_driver.py - change adress in driver for ex 0x27h
Please check with i2cdetect -y 1 (or i2cdetect -y 0 on Raspberry v1 B)

# -*- coding: utf-8 -*-
# Original code found at:
# https://gist.github.com/DenisFromHR/cc863375a6e19dce359d

"""
Compiled, mashed and generally mutilated 2014-2015 by Denis Pleic
Made available under GNU GENERAL PUBLIC LICENSE

# Modified Python I2C library for Raspberry Pi
# as found on http://www.recantha.co.uk/blog/?p=4849
# Joined existing 'i2c_lib.py' and 'lcddriver.py' into a single library
# added bits and pieces from various sources
# By DenisFromHR (Denis Pleic)
# 2015-02-10, ver 0.1

"""

# i2c bus (0 -- original Pi, 1 -- Rev 2 Pi)
I2CBUS = 1

# LCD Address
ADDRESS = 0x27

import smbus
from time import sleep

class i2c_device:
   def __init__(self, addr, port=I2CBUS):
      self.addr = addr
      self.bus = smbus.SMBus(port)

# Write a single command
   def write_cmd(self, cmd):
      self.bus.write_byte(self.addr, cmd)
      sleep(0.0001)

# Write a command and argument
   def write_cmd_arg(self, cmd, data):
      self.bus.write_byte_data(self.addr, cmd, data)
      sleep(0.0001)

# Write a block of data
   def write_block_data(self, cmd, data):
      self.bus.write_block_data(self.addr, cmd, data)
      sleep(0.0001)

# Read a single byte
   def read(self):
      return self.bus.read_byte(self.addr)

# Read
   def read_data(self, cmd):
      return self.bus.read_byte_data(self.addr, cmd)

# Read a block of data
   def read_block_data(self, cmd):
      return self.bus.read_block_data(self.addr, cmd)


# commands
LCD_CLEARDISPLAY = 0x01
LCD_RETURNHOME = 0x02
LCD_ENTRYMODESET = 0x04
LCD_DISPLAYCONTROL = 0x08
LCD_CURSORSHIFT = 0x10
LCD_FUNCTIONSET = 0x20
LCD_SETCGRAMADDR = 0x40
LCD_SETDDRAMADDR = 0x80

# flags for display entry mode
LCD_ENTRYRIGHT = 0x00
LCD_ENTRYLEFT = 0x02
LCD_ENTRYSHIFTINCREMENT = 0x01
LCD_ENTRYSHIFTDECREMENT = 0x00

# flags for display on/off control
LCD_DISPLAYON = 0x04
LCD_DISPLAYOFF = 0x00
LCD_CURSORON = 0x02
LCD_CURSOROFF = 0x00
LCD_BLINKON = 0x01
LCD_BLINKOFF = 0x00

# flags for display/cursor shift
LCD_DISPLAYMOVE = 0x08
LCD_CURSORMOVE = 0x00
LCD_MOVERIGHT = 0x04
LCD_MOVELEFT = 0x00

# flags for function set
LCD_8BITMODE = 0x10
LCD_4BITMODE = 0x00
LCD_2LINE = 0x08
LCD_1LINE = 0x00
LCD_5x10DOTS = 0x04
LCD_5x8DOTS = 0x00

# flags for backlight control
LCD_BACKLIGHT = 0x08
LCD_NOBACKLIGHT = 0x00

En = 0b00000100 # Enable bit
Rw = 0b00000010 # Read/Write bit
Rs = 0b00000001 # Register select bit

class lcd:
   #initializes objects and lcd
   def __init__(self):
      self.lcd_device = i2c_device(ADDRESS)

      self.lcd_write(0x03)
      self.lcd_write(0x03)
      self.lcd_write(0x03)
      self.lcd_write(0x02)

      self.lcd_write(LCD_FUNCTIONSET | LCD_2LINE | LCD_5x8DOTS | LCD_4BITMODE)
      self.lcd_write(LCD_DISPLAYCONTROL | LCD_DISPLAYON)
      self.lcd_write(LCD_CLEARDISPLAY)
      self.lcd_write(LCD_ENTRYMODESET | LCD_ENTRYLEFT)
      sleep(0.2)


   # clocks EN to latch command
   def lcd_strobe(self, data):
      self.lcd_device.write_cmd(data | En | LCD_BACKLIGHT)
      sleep(.0005)
      self.lcd_device.write_cmd(((data & ~En) | LCD_BACKLIGHT))
      sleep(.0001)

   def lcd_write_four_bits(self, data):
      self.lcd_device.write_cmd(data | LCD_BACKLIGHT)
      self.lcd_strobe(data)

   # write a command to lcd
   def lcd_write(self, cmd, mode=0):
      self.lcd_write_four_bits(mode | (cmd & 0xF0))
      self.lcd_write_four_bits(mode | ((cmd << 4) & 0xF0))

   # write a character to lcd (or character rom) 0x09: backlight | RS=DR<
   # works!
   def lcd_write_char(self, charvalue, mode=1):
      self.lcd_write_four_bits(mode | (charvalue & 0xF0))
      self.lcd_write_four_bits(mode | ((charvalue << 4) & 0xF0))
  
   # put string function with optional char positioning
   def lcd_display_string(self, string, line=1, pos=0):
    if line == 1:
      pos_new = pos
    elif line == 2:
      pos_new = 0x40 + pos
    elif line == 3:
      pos_new = 0x14 + pos
    elif line == 4:
      pos_new = 0x54 + pos

    self.lcd_write(0x80 + pos_new)

    for char in string:
      self.lcd_write(ord(char), Rs)

   # clear lcd and set to home
   def lcd_clear(self):
      self.lcd_write(LCD_CLEARDISPLAY)
      self.lcd_write(LCD_RETURNHOME)

   # define backlight on/off (lcd.backlight(1); off= lcd.backlight(0)
   def backlight(self, state): # for state, 1 = on, 0 = off
      if state == 1:
         self.lcd_device.write_cmd(LCD_BACKLIGHT)
      elif state == 0:
         self.lcd_device.write_cmd(LCD_NOBACKLIGHT)

   # add custom characters (0 - 7)
   def lcd_load_custom_chars(self, fontdata):
      self.lcd_write(0x40);
      for char in fontdata:
         for line in char:
            self.lcd_write_char(line)