This new Adafruit plate makes it easy to use a 16x2 Character LCD. We
really like the range of LCDs we stock in the shop, such as our classic
blue & white as well as the fancy
RGB negative and
RGB positive.
Unfortunately, these LCDs do require quite a few digital pins, 6 to
control the LCD and then perhaps another 3 to control the RGB backlight
for a total of 9 pins. That's nearly all the GPIO available on a Raspberry Pi!
With this in mind, we wanted to make it easier for people to get these
LCD into their projects so we devised a Pi plate that lets you control a 16x2 Character LCD, up to 3 backlight pins AND 5 keypad pins using only the two I2C pins on the Pi! The
best part is you don't really lose those two pins either, since you can
stick i2c-based sensors, RTCs, etc and have them share the I2C bus.
This is a super slick way to add a display without all the wiring
hassle.
This plate is perfect for when you want to build a stand-alone project
with its own user interface. The 4 directional buttons plus select
button allows basic control without having to attach a bulky computer.
The kit is designed for any Raspberry Pi - version 1 and 2.
If you want plug in a Cobbler or Gertboard at the same time, check out our Stacking Header, you can fit an IDC cable over it if the Plate is assembled with this part.
Check to make sure your kit comes with the following parts.Sometimes we
make mistakes so double check everything and email support@adafruit.com
if you need replacements!
We recently adjusted the kit so the buttons are on the RIGHT side instead of the left. The parts list is otherwise the same, its just a little more stable than before
1) Resistors
There is a total of 3 resistors in this kit. For resistors labeled RED and BLUE on the PCB, they are 1/4W 5% 220 ohm resistors (Red, Red, Brown, Gold). For the resistor labeled GREEN on the PCB, it is a 1/4W 5% 330 ohm resistor (Orange Orange Brown Gold).
2) Potentiometer
There is one 10k trim potentiometer. This part will go in the spot labeled Contrast
3) Pushbuttons
There are a total of 5 x 6mm tactile switch
pushbuttons. These will be used in the UP, DOWN, LEFT, RIGHT and SELECT locations on the PCB.
4) i2c Port Expander Chip
There is one of these MCP23017 i2c (16
input/output) port expander chips in the kit. This is how we are able
to only use 2 R-Pi pins to run the entire LCD and buttons.
Click here for more info on this chip.
5) Male Header Pins
There is one strip of 36 male header pins
in the kit. These will be used to attach the LCD to the PCB.
6) Printed Circuit Board
There will be one PCB in the kit as shown above.
7) Raspberry Pi Plate Header
There will be one extra-tall 26 pin female header for plugging into the Pi
8) Bumper
There will be one rubber bumper as shown above
Additional
You'll want an LCD to place into the shield. This
isn't included by default since a lot of people already have LCDs they
may want to use. (We do sell these in packs however so chances are you
did get an LCD with your order).
Your LCD may have 16 pins (Monochrome) or 18 pins (RGB) and may have 2 rows of connectors or one. This is normal and does not affect the display
You can also use 16x2 LCDs that are the same size that do not have an RGB backlight, or have no backlight at all.
We carry Negative type or Positive type LCDs as well as Blue and White LCDs
The backlights will not turn on until you have the code running so don't be alarmed if nothing lights up when you plug in the plate! If you have a 'positive' style LCD, you may see some squares on the first line, that's normal
Setting up your Pi for I2C
For a more basic introduction to setting up I2C on your Pi then you may wish to take a diversion to this Adafruit tutorial:
http://learn.adafruit.com/adafruits-raspberry-pi-lesson-4-gpio-setup/configuring-i2cIf you're using Occidentalis, you can skip this next step, but for Raspbian users, edit /etc/modules (
sudo nano /etc/modules) and add:
i2c-bcm2708
i2c-dev
to the end of the file. Then save and reboot to enable the hardware I2C driver.
Before you can get started with I2C on the Pi, you'll need to run
through a couple quick steps from the console. Just enter the following
commands to add SMBus support (which includes I2C) to Python:
sudo apt-get install python-smbus
sudo apt-get install i2c-tools
sudo apt-get install python-smbus
sudo apt-get install i2c-tools
i2c-tools isn't strictly required, but it's a useful package since you
can use it to scan for any I2C or SMBus devices connected to your board.
If you know something is connected, but you don't know it's 7-bit I2C
address, this library has a great little tool to help you find it:
sudo i2cdetect -y 0 (if you are using a version 1 Raspberry Pi)
sudo i2cdetect -y 1 (if you are using a version 2 Raspberry Pi)
sudo i2cdetect -y 0 (if you are using a version 1 Raspberry Pi)
sudo i2cdetect -y 1 (if you are using a version 2 Raspberry Pi)
This will search /dev/i2c-0 or /dev/i2c-1 for all address, and if an
Adafruit LCD Plate is connected, it should show up at 0x20
Once both of these packages have been installed, you have everything you
need to get started accessing I2C and SMBus devices in Python.
Using the example Python code
The LCD Pi Plate Python code for Pi is available on Github at
https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-CodeThe easiest way to get the code onto your Pi is to hook up an Ethernet
cable, and clone it directly using 'git', which is installed by default
on most distros. Simply run the following commands from an appropriate
location (ex. "/home/pi"):
sudo apt-get install git
git clone https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code.git
cd Adafruit-Raspberry-Pi-Python-Code
cd Adafruit_CharLCDPlate
sudo apt-get install git
git clone https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code.git
cd Adafruit-Raspberry-Pi-Python-Code
cd Adafruit_CharLCDPlate
You will also need to install RPi.GPIO, the python library for Pi that allows easy GPIO access. On Raspbian, just run
sudo apt-get install python-dev
sudo apt-get install python-rpi.gpio
Testing the Library
Once the code has be downloaded to an
appropriate folder, and you have your LCD Plate properly connected, you can
start with the basic demo display, which is run by simply executing the library file:
sudo python Adafruit_CharLCDPlate.py
sudo python Adafruit_CharLCDPlate.py
If you have a rev 2 (512MB) Pi, or if you're not getting anything displaying, it might be due to the I2C bus number change in the Pi hardware. Edit Adafruit_CharLCDPlate.py using a command like "nano Adafruit_CharLCDPlate.py". Find the "Test code" section near the end of the file, and change the line
lcd = Adafruit_CharLCDPlate()
to
lcd = Adafruit_CharLCDPlate(busnum = 0)
for a Rev 1 Pi, or to
lcd = Adafruit_CharLCDPlate(busnum = 1)
for a Rev 2 Pi.
Adjusting Contrast
The plate uses a character LCD with an
external contrast potentiometer. The first time you use it, adjust the
potentiometer in the bottom right until you see the text clearly. If you
don't upload code to the Pi, some boxes may appear instead, or you may see nothing at all.
Press some buttons!
Now you can press the buttons to see text and color change.
If you have a blue/white monochrome display the backlight will 'turn off' when pressing some buttons because it does not have the other LEDs installed. This is normal! (The library assumes you have an RGB LCD, there's no way for it to detect that it's actually monochrome)
Using the library code
Interfacing with the python example code is fairly easy! Inside the Adafruit_CharLCDPlate
folder you'll find a
testLCD.py python script. The script does a few things, at the top it imports all the sub-modules. You'll need to have the
Adafruit_I2C.py,
Adafruit_MCP230xx.py and
Adafruit_CharLCDPlate.py python files to be in the same directory so be sure to copy them to your final destination.
Next it initializes the plate with
lcd = Adafruit_CharLCDPlate() - this creates the lcd object and starts communicating with the plate to set up the LCD and buttons
After initialization, you can clear the display with
lcd.clear() and write text with
lcd.message("text goes here") don't forget that its only 16 characters per line, and it does not automatically wrap lines. To insert a newline use the special '\n' character such as shown in the command:
lcd.message("Adafruit RGB LCD\nPlate w/Keypad!")Next you can set the backlight with
lcd.backlight(lcd.COLORNAME) where
COLORNAME is RED, YELLOW, GREEN, TEAL, BLUE, VIOLET for RGB LCD's or for monochrome LCDs, just use ON and OFF
Finally, you can ask the plate which buttons are pressed with
buttonPressed(lcd.BUTTONNAME) where BUTTONNAME is
LEFT RIGHT UP DOWN or
SELECT. This is not an interrupt-driven library so you can't have an interrupt go off when a button in pressed, instead you'll have to query the button in a loop.
That's it! If you want to make detailed messages,
use the python string formatting commands to create a string and then write that string with
message()
Adafruit's Pi Python codebaseCheck the Usage page for how to install the example python code directly from your Pi using git.
