Using the YwRobot to control a 20×4 line display via I2C on a Raspberry PI, what could be easier.

Well, If all of the code was only for an arduino and there being no actual documentation or wiring diagram. Note: Example code IS NOT documentation.

Hey Ho, After some playing around I found the pin arrangement


addr, en,rw,rs,d4,d5,d6,d7,bl
0x27, 2, 1, 0, 4, 5, 6, 7, 3

0x27 is the i2c port address (bus 1 on newer PI’s)

I found this code snippet for a different set of boards http://www.rpiblog.com/2012/07/interfacing-16×2-lcd-with-raspberry-pi.html which was near, but made the display backlight flash and no text output.

So the hacking started…

Basically all of the control lines were on different pins, and I needed to control the backlight (via a wrapper on the i2c write code)

pylcdlib.py
import smbus
from time import *

#
# Modified from http://www.rpiblog.com/2012/07/interfacing-16×2-lcd-with-raspberry-pi.html to run
# 20×4 line display with YwRobot LCM1602 IIC V1 backpack
#

# General i2c device class so that other devices can be added easily
class i2c_device:
def __init__(self, addr, port):
self.addr = addr
self.bus = smbus.SMBus(port)

def write(self, byte):
self.bus.write_byte(self.addr, byte)

def read(self):
return self.bus.read_byte(self.addr)

def read_nbytes_data(self, data, n): # For sequential reads > 1 byte
return self.bus.read_i2c_block_data(self.addr, data, n)

class lcd:
#initializes objects and lcd
”’
Port definitions
addr, en,rw,rs,d4,d5,d6,d7,bl
0x27, 2, 1, 0, 4, 5, 6, 7, 3

”’

def __init__(self, addr, port):
self.lcd_device = i2c_device(addr, port)

self.backlight=1; #default to backlight on

def lcd_init(self):
#set 4 bit mode
self.lcd_device_writebl(0x30) #write
self.lcd_strobe()
sleep(0.005)
self.lcd_strobe()
sleep(0.005)
self.lcd_strobe()
sleep(0.005)
self.lcd_device_writebl(0x20)
self.lcd_strobe()

self.lcd_write(0x28)
self.lcd_write(0x08)
self.lcd_write(0x01)
self.lcd_write(0x06)
self.lcd_write(0x0C)
self.lcd_write(0x0F)

#wrapper to self.lcd_device.write fir backlight control
def lcd_device_writebl(self,value):
if self.backlight:
self.lcd_device.write(value | 0x08);
else:
self.lcd_device.write(value)

# control backlight on=1 or off=0
def lcd_backlight(self,on):
self.backlight=on
self.lcd_strobe()

# clocks EN to latch command
def lcd_strobe(self):
#bit 2
self.lcd_device_writebl((self.lcd_device.read() | 0x04))
self.lcd_device_writebl((self.lcd_device.read() & 0xFB))

# write a command to lcd
def lcd_write(self, cmd):
self.lcd_device_writebl((cmd >> 4)<<4)
self.lcd_strobe()
self.lcd_device_writebl((cmd & 0x0F)<<4) self.lcd_strobe() # self.lcd_device_writebl(0x0) # write a character to lcd (or character rom) def lcd_write_char(self, charvalue): self.lcd_device_writebl((0x01 | (charvalue >> 4)<<4))
self.lcd_strobe()
self.lcd_device_writebl((0x01 | (charvalue & 0x0F)<<4))
self.lcd_strobe()
self.lcd_device_writebl(0x0)

# put char function
def lcd_putc(self, char):
self.lcd_write_char(ord(char))

# put string function
def lcd_puts(self, stringin, line):
if line == 1:
self.lcd_write(0x80)
if line == 2:
self.lcd_write(0xC0)
if line == 3:
self.lcd_write(0x94)
if line == 4:
self.lcd_write(0xD4)

string=stringin + ” ” #blank out rest of line
string=string[0:20];#limit lines to 20 char

for char in string:
self.lcd_putc(char)

# clear lcd and set to home
def lcd_clear(self):
self.lcd_write(0x1)
self.lcd_write(0x2)

def lcd_cursoroff(self):
self.lcd_write(0x0c) #cursor and blink off

# add custom characters (0 – 7)
def lcd_load_custon_chars(self, fontdata):
self.lcd_device.bus.write(0x40);
for char in fontdata:
for line in char:
self.lcd_write_char(line)

From:
http://www.ideaheap.com/2013/07/stopping-sd-card-corruption-on-a-raspberry-pi/
Read for more info

The biggest offender for Filesystem writes on any linux system is logging. If you are like me, you don’t really look at /var/log after a recycle anyways. This area, and /var/run, a location where lock files, pid files and other “stuff” shows up, are the most common areas for mess-ups. Take a look at your blinking FS light on the board. Our goal is to make that light stay off as long as possible.

Set up tmpfs mounts for worst offenders.

The following two lines should be added to /etc/fstab:

none        /var/run        tmpfs   size=1M,noatime         00
none        /var/log        tmpfs   size=1M,noatime         00

There’s more, however. By default, linux also records when a file was last accessed.
That means that every time you read a file, the SD card is written to. That is no good! Luckily, you can specify the “noatime” option to disable this filesystem feature. I use this flag generously.

Also, for good measure, i set /boot to read-only. There’s really no need to regularly update this, and you can come back here and change it to “defaults” and reboot when you need to do something.

After this, /etc/fstab should look as follows:

proc            /proc               proc    defaults                    0   0
/dev/mmcblk0p1  /boot               vfat    ro,noatime                  0   2
/dev/mmcblk0p2  /                   ext4    defaults,noatime            0   1
none        /var/run        tmpfs   size=1M,noatime             0   0
none        /var/log        tmpfs   size=1M,noatime             0   0

Go ahead and reboot now to see things come up. Check the Filesystem light on your raspberry pi after it’s fully booted. You should see no blinking at all.

Disable swapping

One protection against SD card corruption is an optional, but potentially “I’m glad i did that” change to disable swapping.

The raspberry pi uses dphys-swapfile to control swapping. It dynamically creates a swap partition based on the available RAM. This tool needs to be used to turn off swap, and then needs to be removed from startup.

Run the following commands to disable swapping forever on your system:

sudo dphys-swapfile swapoff
sudo dphys-swapfile uninstall
sudo update-rc.d dphys-swapfile remove

After doing this, call free -m in order to see your memory usage:

pi@raspberrypi ~ $ free -m
             total       used       free     shared    buffers     cached
Mem:           438         59        378          0          9         27
-/+ buffers/cache:         22        416
Swap:            0          0          0

If you reboot, and run a free -m again, you should still see swap at 0. Now we don’t have to worry about tmpfs filesystems swapping out to hard disk!

From:
http://www.ideaheap.com/2013/07/stopping-sd-card-corruption-on-a-raspberry-pi/
Read for more info

To set up wifi access using just the command line

edit /etc/network/interfaces

Add the lines

allow-hotplug wlan0
auto wlan0

iface wlan0 inet dhcp
wpa-ssid “ssid”
wpa-psk “password”