A LCD display my RPi and RPi-Monitor

I saw on the internet that it is possible to use a LCD to display information from the Raspberry Pi. RPi-Monitor is gathering a lot of information and it could be interesting to have such an information available without a computer. So I decided to purchase a PCD8544 from dx.com.

Photo from Flickr  cc-by by arduinolabs

This post is describing how to acquire, connect and use such a component with he Raspberry Pi and gives an example showing how to connect it with RPi-Monitor.



Step 1: The acquisition

I found on the Internet a site reselling the PCD8544 for few euros (dx.com). After a moment of hesitation, I decided to give a try and I purchased it. It was the 16th of may.

The 27th of may, I received a e-mail saying that my purchase was partially shipped, one element is no more available (I've been reimbursed) and a last element will be sent later...

I finally received all my good 4 weeks after the initial purchase order. This site doesn't contradict its reputation: It delivers the good but you have to be patient... very patient ;-).

PCD8544 LCD screen

Step 2: The connection

The PCD8544 comes in two parts (the lcd screen and the pins) that need to be soldered together. Once done, it can be installed in the breadboard as shown in the drawing bellow:

Schema made with Fritzing (fritzing.org)

Note: If you want to reproduce this assembly, check carefully the pin order, it may be different.

Step 3: The preparation

My first goal is to test this new display. I look on the internet and find different solution using Python or C. After few tries, I decided to use Python based on the information shared into this post.

To use the PCD8544 display we need to install few software and load a kernel module.

First, let's install wiringpi2 from drogon.net

git clone git://git.drogon.net/wiringPi

cd wiringPi

./build

Once wiringpi is installed, it is possible to test it with the following command:

gpio readall

 +-----+-------+------+----+-Rev2-----+----+------+-------+-----+
 | wPi |  Name | Mode | Val| Physical |Val | Mode | Name  | wPi |
 +-----+-------+------+----+----++----+----+------+-------+-----+
 |     |  3.3v |      |    |  1 || 2  |    |      | 5v    |     |
 |   8 |   SDA |   IN | Lo |  3 || 4  |    |      | 5V    |     |
 |   9 |   SCL |   IN | Lo |  5 || 6  |    |      | 0v    |     |
 |   7 | GPIO7 |   IN | Lo |  7 || 8  | Lo | ALT0 | TxD   | 15  |
 |     |    0v |      |    |  9 || 10 | Lo | ALT0 | RxD   | 16  |
 |   0 | GPIO0 |   IN | Hi | 11 || 12 | Hi | OUT  | GPIO1 | 1   |
 |   2 | GPIO2 |   IN | Lo | 13 || 14 |    |      | 0v    |     |
 |   3 | GPIO3 |   IN | Hi | 15 || 16 | Lo | OUT  | GPIO4 | 4   |
 |     |  3.3v |      |    | 17 || 18 | Lo | OUT  | GPIO5 | 5   |
 |  12 |  MOSI | ALT0 | Hi | 19 || 20 |    |      | 0v    |     |
 |  13 |  MISO | ALT0 | Hi | 21 || 22 | Hi | IN   | GPIO6 | 6   |
 |  14 |  SCLK | ALT0 | Hi | 23 || 24 | Lo | ALT0 | CE1   | 10  |
 |     |    0v |      |    | 25 || 26 | Lo | ALT0 | CE1   | 11  |
 +-----+-------+------+----+----++----+----+------+-------+-----+

Now, install the python binding of wiringpi:

sudo apt-get install python-dev python-imaging python-imaging-tk python-pip

sudo pip install wiringpi2

The program we will use require spidev to be activated. The kernel module should then be activated.
To do so, comment the line blacklist spi-bcm2708 by adding a heading # in the file /etc/modprobe.d/raspi-blacklist.conf then reboot the Raspberry Pi to activate this module.

Finally install spidev python library:

sudo pip install spidev

The prerequisite are now installed. In next chapter we will see how to install the python library in charge of driving the PCD8544 LCD and how to use it.

Step 4: The installation

Into Raspberry Pi forum, an interesting post catch my attention. I used it as the base to control the LCD.
The library written Richard Hull's is also interesting I then took this as a example to create module that can be directly installed on the Raspberry Pi.
This pcd8544 library resulting is available into its own dedicated repository in github.
To install it, execute the following commands:

git clone https://github.com/XavierBerger/pcd8544.git

cd pcd8544

./setup.py clean build 

sudo ./setup.py install

 You can now test the installation with the proposed examples:

cd examples

./pi_logo.py

 If installation works properly, you should see the following screen:

You can try to execute other examples to see what the library is capable to do with this LCD.

Step 5: The utilization

As I said in introduction, RPi-Monitor is gathering a lot of information and some of them may be interesting to have without having to start a PC. Information are made available from the embedded web server. To get and display the information we then just have to create a web client and use the library to display.

For people interesting about learning development I did comment my code:

#!/usr/bin/env python import httplib, time, os, sys, json import pcd8544.lcd as lcd # class Process dedicated to process data get from Client # and send information to LCD and console class Process: # Process constructor def __init__(self): # Initialize LCD lcd.init() # Turn the backlight on lcd.backlight(1) def run(self, jsonString): # Parse data as json data = json.loads( jsonString ) # Try to get data from json or return default value try: rpi_temperature = data['living_room_temp'] except: rpi_temperature="--.---" try: rpi_humidity = data['humidity'] except: rpi_humidity = "--" # Construct string to be displayed on screens temperature = "Temp: %s C" % rpi_temperature humidity = "Humidity: %s %%" % rpi_humidity lcd.gotorc(0,1) lcd.text("RPi-Monitor") lcd.gotorc(2,0) lcd.text(temperature) lcd.gotorc(3,0) lcd.text(humidity) # Also print string in console os.system("clear") print " RPi-Monitor " print print temperature print humidity print time.sleep(1) # Class client design to work as web client and get information # from RPi-Monitor embedded web server class Client: # Client constructor def __init__(self): # Create a Process object self.process = Process() def run(self): # Infinite loop while True: try: # Initiate a connection to RPi-Monitor embedded server connection = httplib.HTTPConnection("localhost", 8888) # Get the file dynamic.json connection.request("GET","/dynamic.json") # Get the server response response = connection.getresponse() if ( response.status == 200 ): # If response is OK, read data data = response.read() # Run process object on extracted data self.process.run(data) # Close the connection to RPi-Monitor embedded server connection.close() finally: # Wait 5 secondes before restarting the loop time.sleep(5) # Main function def main(): try: # Create a Client object client = Client() # Run it client.run() except KeyboardInterrupt: # if Ctrl+C has been pressed # turn off the lcd backlight lcd.backlight(0); # exit from the program sys.exit(0) # Execute main if the script is directly called if __name__ == "__main__": main()

This code is dedicated to extract the living room temperature and humidity from RPi-Monitor information.
Copy this code into a file (rpimonitor-testlcd.py) the make this file executable (chmod +x rpimonitor-testlcd.py) then execute (./rpimonitor-testlcd.py) it to see: