I wasn't aware that the SparkFun module provided more than just serial to parallel conversion.

The SainSmart backpack is a simple (and cheap) device. I just looked, their 2 x 16 LCD with i2c backpack is under $10 US. There are other similar backpacks out there that you can wire up yourself to an LCD display which are now really cheap. The disadvantage is that the information on using them is poor.

While trying to get mine working I read numerous posts from people who could not get theirs to work. In the end I went back to basics, and worked out how the backpacks work and how the LCD 4-bit mode works, and then avoided the high level libraries. Simple i2c communication using the HiPi::BCM2835::I2C was all that was needed. The module is described as: The HiPi::BCM2835::I2C module provides direct access to the Broadcom I2C Serial peripheral.

After that it came down to understanding the commands and the way the parallel side of the i2c backpack was connected to the LCD.

I will write up some more detailed notes on the 8-bit/4-bit issue and initialization and post it later

I have a Perl script that collects data from an spi bus-attached ADC that monitors some voltages. I should tidy up the script and post that as well

anita2R

I went back and looked at my chipKIT code. Turns out my Sparkfun LCD is a SPI interface. My SF 4 digit LED display uses I2C. In either case neither required any bit twiddling. Their backpack has an on-board PIC that abstracts out the HD44780 handling. Ease of use and no soldering comes at a higher price(double) than you have with the SainSmart product.

Update:I read through the HiPi docs last night. Good stuff! The developer, Mark Dootson, has done much work on wxPerl and I believe that wxPerl will run on the RPI, if you need to do any GUI work.

For Example:

// SerLCDTest.pde - Serial Interface Version for use with the chipKIT 
+UNO
//
// This display uses the HD44780 LCD controller and a PIC16F688 serial
+ interface
//
// Test file for the Sparkfun Serial LCD used with the chipKIT UNO
//    Uses UART1(pin 40 TX) so UART0/USB can be used for debug message
+s
//    Combined header and library files for initial testing of the dis
+play.
//    Hope to split into a library after testing.
//
// James M. Lynes, Jr.
// Last Modified: December 24,2012
//
// This code is public domain, but you buy me a beer(or Dr. Pepper)
// if you use this and we meet some day(Beerware License).
//
// Constant Definitions
//
// Display Commands
//
#define    COMMAND        0xFE        // Command Code
#define    CLEARDISP    0x01        // Clear the display
#define    CURSORHOME    0x02        // Send the cursor home
#define    CURSORRIGHT    0x14        // Move the cursor right one pos
+ition
#define    CURSORLEFT    0x10        // Move cursor left one position
#define    SCROLLRIGHT    0x1C        // Scroll the display right
#define    SCROLLLEFT    0x18        // Scroll the display left
#define    DISPLAYON    0x0C        // Turn the display on
#define DISPLAYOFF    0x08        // Turn the display off
#define    UCURSORON    0x0E        // Turn underline cursor on
#define UCURSOROFF    0x0C        // Turn underline cursor off
#define    BOXCURSORON    0x0D        // Turn box cursor on
#define    BOXCURSOROFF    0x0C        // Turn box cursor off
#define    LINE1        0x80        // Row 1 COl 1 Address
#define    LINE2        0xC0        // Row 2 COl 1 Address
#define    RESET        0x12        // Reset code, send at 9600 baud i
+mmediately after POR
//
// Configuration Commands
//
#define    CONFIG        0x7C        // Configuration Code
#define    B2400        0x0B        // Set 2400  baud
#define B4800        0x0C        // Set 4800  baud
#define    B9600        0x0D        // Set 9600  baud
#define B144K        0x0E        // Set 14400 baud
#define    B192K        0x0F        // Set 19200 baud
#define B384K        0x10        // Set 38400 baud
#define SAVESPLASH    0x0A        // Save a new splash message
#define    TOGGLESPLASH    0x09        // Toggle splash screen on and 
+off
#define    BACKLIGHTOFF    0x80        // Turn the backlight off
#define    BACKLIGHTMED    0x8F        // Turn the backlight to 50%
#define BACKLIGHTHIGH    0x9D        // Turn the backlight to 100%
//
// Misc Defines
//
#define    LCDTYPE        0x03        // Type 2 line x 16 characters
#define    LCDDelay    0x10        // General delay timer
#define    LCDDelay2    0x200        // Scroll timer
//
// Function Protypes
//
void    LCDClear();            // Clear the display
void    LCDSelectLineOne();        // Position cursor to the beginning
+ of line 1
void    LCDSelectLineTwo();        // Position cursor to the beginning
+ of Line 2
void    LCDGoTo(int position);        // Position cursor to a specific
+ character 0-15, 16-31
void    LCDBacklightOn();        // Turn the backlight on
void    LCDBacklightOff();        // Turn the backlight off
void    LCDCursorHome();        // Position cursor to home
void    LCDCursorRight();        // Set cursor to move left to rght
void    LCDCursorLeft();        // Set cursor to move right to left
void    LCDScrollRight();        // Scroll the display right
void    LCDScrollLeft();        // Scroll the dispaly left
void    LCDDisplayOn();            // Turn the display on
void    LCDDisplayOff();        // Turn the display off
void    LCDUCursorOn();            // Turn the underline cursor on
void    LCDUCursorOff();        // Turn the underline cursor off
void    LCDBoxCursorOn();        // Turn the box cursor on
void    LCDBoxCursorOff();        // Turn the box cousor off
void    LCDBlackStart();        // Restart from an unknown state
void    LCDSaveSplash(char*, char*);    // Save a new spash display
void    LCDToggleSplash();        // Toggle the splash display on/off/
+on
void    LCDSetBrightness(int);        // Set the screen brightness 128
+-157(0x80-0x9D)
void    LCDSetBaud(int);        // Set a new baud rate
//
// Test Function Prototypes
//
void    tstwrite();            // Write out two lines of text
void    tstmoves();            // Try some cursor moves
void    tstscroll();            // Try some scrolling
void    tstbrightness();        // Cycle the backlight high to off
//
// Main Program
//
void    setup()
{
    delay(3000);            // Time to allow the splash screen to disp
+lay
    Serial.begin(9600);        // Start serial communications for debu
+g messages
    Serial.println("Initialized UNO Serial/USB Port");
    Serial1.begin(9600);        // Initialize the UART1 hardware
    Serial.println("Initialized UNO UART1");
    LCDClear();            // Reset the LED display, cursor to positio
+n 1
    Serial.println("Cleared the LCD Display");
    LCDSetBrightness(BACKLIGHTHIGH);// Set display to max brightness
}

void loop()
{
    Serial.println("Mainloop");
    Serial.println("Writes");
    tstwrite();
    delay(2000);
    Serial.println("Moves");
    tstmoves();
    delay(10000);
    Serial.println("Scrolls");
    tstscroll();
    delay(2000);
//    Serial.println("Brightness");
//    tstbrightness();
//    delay(2000);
}

// Test Subroutines

void    tstwrite()
{
    LCDClear();
    LCDSelectLineOne();
    Serial1.print("Merry Christmas");
    LCDSelectLineTwo();
    Serial1.print(" to my Sweetie ");
}

void    tstmoves()
{
    LCDClear();
    LCDSelectLineOne();
    Serial1.print("789ABCDEF6543210");
    LCDSelectLineTwo();
    LCDGoTo(24);
    Serial1.print("@");
    LCDCursorRight();
    LCDCursorRight();
    Serial1.print("#");
    LCDCursorHome();
    Serial1.print("$");
    LCDCursorHome();
    LCDCursorLeft();
//    LCDCursorLeft();
    Serial1.print("%");
}

void    tstscroll()
{
    LCDClear();
    LCDSelectLineOne();
    Serial1.print("0123456789ABCDEF");
    delay(LCDDelay);
    for(int i=1 ; i<9; i++){
        LCDScrollLeft();
    }
    for(int i=1 ; i<9; i++){
        LCDScrollRight();
    }
}

void    tstbrightness()
{
    tstwrite();
    LCDSetBrightness(BACKLIGHTHIGH);
    LCDSetBrightness(BACKLIGHTMED);
    LCDSetBrightness(BACKLIGHTOFF);
}

// Library Subroutines

void    LCDClear()
{
    Serial1.write(COMMAND);
    Serial1.write(CLEARDISP);        // Clear the display
    delay(LCDDelay);
}

void    LCDSelectLineOne()
{
    Serial1.write(COMMAND);
    Serial1.write(LINE1);            // Select line 1
    delay(LCDDelay);    
}

void    LCDSelectLineTwo()
{
    Serial1.write(COMMAND);
    Serial1.write(LINE2);            // Select line 2
    delay(LCDDelay);
}

void    LCDGoTo(int position)
{
    if(position < 16)            // Go to specific position 0-31
    {
        Serial1.write(COMMAND);
        Serial1.write(position + 128);
    }
    else if(position < 32)
    {
        Serial1.write(COMMAND);
        Serial1.write(position + 48 + 128);
    }
    else
    {
        LCDGoTo(0);
    }
    delay(LCDDelay);
}

void    LCDBacklightOn()
{
    Serial1.write(CONFIG);
    Serial1.write(BACKLIGHTHIGH);        // Turn the backlight on
    delay(LCDDelay);
}

void    LCDBacklightOff()
{
    Serial1.write(CONFIG);
    Serial1.write(BACKLIGHTOFF);        // Turn the backlight off
    delay(LCDDelay);
}

void    LCDCursorHome()
{
    Serial1.write(COMMAND);
    Serial1.write(CURSORHOME);        // Position the cursor to home
    delay(LCDDelay);
}

void    LCDCursorRight()
{
    Serial1.write(COMMAND);
    Serial1.write(CURSORRIGHT);        // Move cursor right one positi
+on
    delay(LCDDelay);
}

void    LCDCursorLeft()
{
    Serial1.write(COMMAND);
    Serial1.write(CURSORLEFT);        // Move cursor left one position
    delay(LCDDelay);
}

void    LCDScrollRight()
{
    Serial1.write(COMMAND);
    Serial1.write(SCROLLRIGHT);        // Scroll the display right one
+ position
    delay(LCDDelay2);
}

void    LCDScrollLeft()
{
    Serial1.write(COMMAND);
    Serial1.write(SCROLLLEFT);        // Scroll the display left one p
+osition
    delay(LCDDelay2);
}

void    LCDDisplayOn()
{
    Serial1.write(COMMAND);
    Serial1.write(DISPLAYON);        // Turn the display on
    delay(LCDDelay);
}

void    LCDDisplayOff()
{
    Serial1.write(COMMAND);
    Serial1.write(DISPLAYOFF);        // Turn the display off
    delay(LCDDelay);
}

void    LCDUCursorOn()
{
    Serial1.write(COMMAND);
    Serial1.write(UCURSORON);        // Turn the underline cursor on
    delay(LCDDelay);
}

void    LCDUCursorOff()
{
    Serial1.write(COMMAND);
    Serial1.write(UCURSOROFF);        // Turn the underline cursor off
    delay(LCDDelay);
}

void    LCDBoxCursorOn()
{
    Serial1.write(COMMAND);
    Serial1.write(BOXCURSORON);        // Turn the box cursor on
    delay(LCDDelay);
}

void    LCDBoxCursorOff()
{
    Serial1.write(COMMAND);
    Serial1.write(BOXCURSOROFF);        // Turn the box cursor off
    delay(LCDDelay);
}

void    LCDBlackStart()
{
    Serial1.write(RESET);            // Restart from unknown condition
    delay(LCDDelay);
}

void    LCDSaveSplash(char *l1, char *l2)
{
    LCDSelectLineOne();            // Replace the splash screen
    Serial1.print(l1);
    LCDSelectLineTwo();
    Serial1.print(l2);
    Serial1.write(CONFIG);
    Serial1.write(SAVESPLASH);
    delay(LCDDelay);
}

void    LCDToggleSplash()
{
    Serial1.write(CONFIG);            // Toggle the splash screen on/o
+ff/on
    Serial1.write(TOGGLESPLASH);
    delay(LCDDelay);
}

void    LCDSetBrightness(int level)
{
    Serial1.write(CONFIG);            // Change the brightness level
    Serial1.write(level);
    delay(LCDDelay);
}

void    LCDSetBaud(int rate)
{
    Serial1.write(CONFIG);            // Change the baud rate
    Serial1.write(rate);
    delay(LCDDelay);
}
[download]

James

There's never enough time to do it right, but always enough time to do it over...

This code uses the HiPi module which seemed to me to require I load the whole GUI (I am using minibian) so I converted a Python demo program to Perl as an illustration of how to use the SMBus module to write to an I2C LCD (16x2). Here is the code:

#!/usr/bin/perl
# Example program which writes to the I2C LCD at address 0x3f.  This w
+as 
# a direct port of the program published by Matt Hawkins on the site
# www.raspberrypi-spy.co.uk.  Port performed by Steve Stock.   
#
use strict;
use warnings;
use Time::HiRes ('usleep');
use Device::SMBus;

my $I2C_ADDR=0x3f;
my $DEVICE_PATH = '/dev/i2c-1';
my $dev = Device::SMBus->new(I2CBusDevicePath => $DEVICE_PATH,
  I2CDeviceAddress => $I2C_ADDR);
my $LCD_WIDTH = 16;
my $LCD_CHR=1;
my $LCD_CMD=0;
my $FILL_CHAR=" ";

my $LCD_LINE_1=0x80;
my $LCD_LINE_2=0xc0;
my $LCD_LINE_3=0x94;
my $LCD_LINE_4=0xd4;

my $LCD_BACKLIGHT=0x08;
my $LCD_BACKLIGHT_OFF=0x00;

my $ENABLE=0b00000100;

my $E_PULSE=500;
my $E_DELAY=500;

sub lcd_toggle_enable {
  my ($bits)=@_;
  usleep($E_PULSE);
  my $rc = $dev->writeByteData(0x00,$bits | $ENABLE);
  $rc = $dev->writeByteData(0x00,$bits & ~$ENABLE);
}


sub lcd_byte {
  my ($bits,$mode) = @_;
  my $bits_high=0;my $bits_low=0;
  $bits_high = $mode | ($bits & 0xf0) | $LCD_BACKLIGHT;
  $bits_low = $mode | (($bits << 4) & 0xf0) | $LCD_BACKLIGHT;
  my $rc = $dev->writeByteData(0x00,$bits_high);  
  lcd_toggle_enable($bits_high);
  $rc = $dev->writeByteData(0x00,$bits_low);
  lcd_toggle_enable($bits_low);
  usleep($E_PULSE);
}

sub lcd_init {
  lcd_byte(0x33,$LCD_CMD);
  lcd_byte(0x32,$LCD_CMD);
  lcd_byte(0x06,$LCD_CMD);
  lcd_byte(0x0c,$LCD_CMD);
  lcd_byte(0x28,$LCD_CMD);
  lcd_byte(0x01,$LCD_CMD);
  usleep($E_PULSE);
}

sub lcd_string {
  my ($message, $line) = @_;
  lcd_byte($line, $LCD_CMD);
  for (0..$LCD_WIDTH) {$message=$message.$FILL_CHAR};
  for (my $i=0;$i<($LCD_WIDTH);$i++) {lcd_byte(ord(substr($message,$i,
+1)),$LCD_CHR);}
}  

# MAIN
while (1==1) {
  lcd_init(); 
  lcd_string("RPiSpy         <",$LCD_LINE_1);
  lcd_string("I2C LCD        <",$LCD_LINE_2);
  sleep(5);
  lcd_string(">         RPiSpy",$LCD_LINE_1);
  lcd_string(">        I2C LCD",$LCD_LINE_2);
  sleep(5);
}
[download]