RaspberryPi/LCD Display

Also see Arduino LCD Display, which was the original.

Overview

See Arduino LCD Display#Overview for an overview of how the LCD display works. It works by communicating with the microcontroller using I2C pins, which provide a way for integrated circuits to communicate with each other.

The Circuit

Breadboard Diagram

Need to make a firtzing diagram for this.

Breadboard Photo

Here's a photo of the breadboard:

Python Sketch

More information about the Raspberry Pi GPIO pinouts and how to control 'em with Python is over on the RaspberryPi/Blink page.

Specifically, here is some Python code written to control GPIO pins on the Raspberry Pi: RaspberryPi/Blink#The_Python_Code

The Code

This section covers the software needed to drive the LCD display via the GPIO pins on the Raspberry Pi.

Adafruit provides an entire package for interfacing with character LCD displays [1]. Unfortunately, however, these are for LCDs that do not have an integrated circuit onboard, and so have a much greater number of pins. This is an excellent illustration of why we would want to install an integrated circuit to control the LCD, rather than controlling the LCD directly.

Without the IC onboard the LCD, we might need to connect up to 16 pins:

Prep the Pi

Make sure you can log in to the Pi. This consists of the following steps:

• Mount the SD card and edit cmdline.txt, hard-code an IP address in cmdline.txt
• Unmount the SD card and insert it back into the Pi and power it up
• Give the Pi a minute to finish booting up, then connect it using an Ethernet cable to your desktop/computer
• Remotely log in to the Pi via SSH

Raspberry Pi GPIO Library

Adafruit code for controlling LCDs from the Raspberry Pi: https://github.com/adafruit/Adafruit_Python_CharLCD

Make sure the RPi-GPIO package is installed:

Download the package on your laptop and copy it over to the Pi:

[laptop] $ wget https://pypi.python.org/packages/source/R/RPi.GPIO/RPi.GPIO-0.5.11.tar.gz
[laptop] $ scp RPi.*.tar.gz pi@169.254.113.200:~/.

Then you install it manually on the Pi:

[pi] $ cd ~
[pi] $ tar xzf RPi*.tar.gz
[pi] $ cd RPi*
[pi] $ sudo python setup.py install

This has other prerequisites, all available from Adafruit on GitHub (need to add links):

Adafruit_Python_PureIO
Adafruit_Python_GPIO
py-spidev

Enable SPI

In order to use the GPIO, you need the GPIO library installed above (which provides bindings between Python and the Raspberry Pi kernel, which contains code to control the pins on-board the Pi).

However, in order to use I2C, which is the protocol used to communicate from one integrated circuit to another, you need to enable SPI on the Raspberry Pi.

This page [2] states that SPI is not enabled by default on Raspbian. However, I had Kali for ARM installed, and SPI was enabled by default. If you run the lsmod command, you can check whether the SPI kernel module is enabled. (This stuff is mostly over my head anyway, but you don't have to understand all the details of what's going on to make it work...)

$  lsmod
Module                  Size  Used by
cfg80211              498967  0
rfkill                 22468  1 cfg80211
snd_soc_wm8804          8209  0
snd_soc_pcm512x_i2c     2562  0
regmap_spi              2307  1 snd_soc_wm8804
snd_soc_tas5713         5858  0
snd_soc_pcm512x        16523  1 snd_soc_pcm512x_i2c
regmap_i2c              3338  3 snd_soc_wm8804,snd_soc_pcm512x_i2c,snd_soc_tas5713
snd_soc_bcm2708_i2s     7595  0
regmap_mmio             3548  1 snd_soc_bcm2708_i2s
snd_soc_core          167442  4 snd_soc_pcm512x,snd_soc_wm8804,snd_soc_tas5713,snd_soc_bcm2708_i2s
snd_compress            8840  1 snd_soc_core
snd_pcm_dmaengine       5770  1 snd_soc_core
snd_pcm                92149  4 snd_soc_pcm512x,snd_soc_wm8804,snd_soc_core,snd_pcm_dmaengine
snd_timer              23475  1 snd_pcm
spi_bcm2708             6006  0
i2c_bcm2708             6244  0
snd                    67406  4 snd_soc_core,snd_timer,snd_pcm,snd_compress
fuse                   92370  1
ipv6                  353829  0

The line we're looking for here relates to SPI:

spi_bcm2708             6006  0

This means we have the SPI kernel module enabled. In case you don't have it enabled, you can find instructions here [3]. Basically, enable the kernel module using modprobe:

$ sudo modprobe spi_bcm2708
$ sudo chown `id -u`.`id -g` /dev/spidev0.*