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Topic: LCD4Bit for 20x4 displays! (Read 20887 times) previous topic - next topic

Vancouver Reefer

Ok guys i need help!!!!

Here is the screen i have:

http://www.futurlec.com/LED/BLUELCD16x2BL.shtml ( but i have the 16x4 verison )

I have copied over the code from Billyboy's post but all i can get on my screen is chinese looking symbols on lines 1 and 3.

Im a complete newb to this so if anyone can see what ive done worng please could you show me my errors!!!

Here is the .cpp file:

LCD4Bit v0.1 16/Oct/2006 neillzero http://abstractplain.net

What is this?
An arduino library for comms with HD44780-compatible LCD, in 4-bit mode (saves pins)

- The original "LiquidCrystal" 8-bit library and tutorial
- DEM 16216 datasheet http://www.maplin.co.uk/Media/PDFs/N27AZ.pdf
- Massimo's suggested 4-bit code (I took initialization from here) http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1144924220/8
See also:
- glasspusher's code (probably more correct): http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1160586800/0#0

Tested only with a DEM 16216 (maplin "N27AZ" - http://www.maplin.co.uk/Search.aspx?criteria=N27AZ)
If you use this successfully, consider feeding back to the arduino wiki with a note of which LCD it worked on.

see the examples folder of this library distribution.


#include "LCD4Bit.h"
extern "C" {
 #include <stdio.h>  //not needed yet
 #include <string.h> //needed for strlen()
 #include <inttypes.h>
 #include "WConstants.h"  //all things wiring / arduino

//command bytes for LCD
#define CMD_CLR 0x01
#define CMD_RIGHT 0x1C
#define CMD_LEFT 0x18
#define CMD_HOME 0x02

// --------- PINS -------------------------------------
//is the RW pin of the LCD under our control?  If we're only ever going to write to the LCD, we can use one less microcontroller pin, and just tie the LCD pin to the necessary signal, high or low.
//this stops us sending signals to the RW pin if it isn't being used.
int USING_RW = false;

//RS, RW and Enable can be set to whatever you like
int RS = 11;
int RW = FALSE;
int Enable = 12;
//DB should be an unseparated group of pins  - because of lazy coding in pushNibble()
int DB[] = {7, 8, 9, 10};  //wire these to DB4~7 on LCD.


//how many lines has the LCD? (don't change here - specify on calling constructor)
int g_num_lines = 2;

//pulse the Enable pin high (for a microsecond).
//This clocks whatever command or data is in DB4~7 into the LCD controller.
void LCD4Bit::pulseEnablePin(){
 // send a pulse to enable
 delay(1);  // pause 1 ms.  TODO: what delay, if any, is necessary here?

//push a nibble of data through the the LCD's DB4~7 pins, clocking with the Enable pin.
//We don't care what RS and RW are, here.
void LCD4Bit::pushNibble(int value){
 int val_nibble= value & 0x0F;  //clean the value.  (unnecessary)

 for (int i=DB[0]; i <= DB[3]; i++) {
   digitalWrite(i,val_nibble & 01);
   val_nibble >>= 1;

//push a byte of data through the LCD's DB4~7 pins, in two steps, clocking each with the enable pin.
void LCD4Bit::pushByte(int value){
 int val_lower = value & 0x0F;
 int val_upper = value >> 4;

//stuff the library user might call---------------------------------
//constructor.  num_lines must be 1 or 2, currently.
LCD4Bit::LCD4Bit (int num_lines) {
g_num_lines = num_lines;
if (g_num_lines < 1)
  g_num_lines = 1;
if (g_num_lines > 4)
  g_num_lines = 4;

void LCD4Bit::commandWriteNibble(int nibble) {
 digitalWrite(RS, LOW);
 if (USING_RW) { digitalWrite(RW, LOW); }

void LCD4Bit::commandWrite(int value) {
 digitalWrite(RS, LOW);
 if (USING_RW) { digitalWrite(RW, LOW); }
 //TODO: perhaps better to add a delay after EVERY command, here.  many need a delay, apparently.

//print the given character at the current cursor position. overwrites, doesn't insert.
void LCD4Bit::print(int value) {
 //set the RS and RW pins to show we're writing data
 digitalWrite(RS, HIGH);
 if (USING_RW) { digitalWrite(RW, LOW); }

 //let pushByte worry about the intricacies of Enable, nibble order.

//print the given string to the LCD at the current cursor position.  overwrites, doesn't insert.
//While I don't understand why this was named printIn (PRINT IN?) in the original LiquidCrystal library, I've preserved it here to maintain the interchangeability of the two libraries.
void LCD4Bit::printIn(char msg[]) {
 uint8_t i;  //fancy int.  avoids compiler warning when comparing i with strlen()'s uint8_t
 for (i=0;i < strlen(msg);i++){

//send the clear screen command to the LCD
void LCD4Bit::clear(){

// initiatize lcd after a short pause
//while there are hard-coded details here of lines, cursor and blink settings, you can override these original settings after calling .init()
void LCD4Bit::init () {
 if (USING_RW) { pinMode(RW,OUTPUT); }


 //The first 4 nibbles and timings are not in my DEM16217 SYH datasheet, but apparently are HD44780 standard...

 // needed by the LCDs controller
 //this being 2 sets up 4-bit mode.
 //todo: make configurable by the user of this library.
 //NFXX where
 //N = num lines (0=1 line or 1=2 lines).
 //F= format (number of dots (0=5x7 or 1=5x10)).
 //X=don't care

 int num_lines_ptn = g_num_lines - 1 << 3;
 int dot_format_ptn = 0x00;      //5x7 dots.  0x04 is 5x10

 commandWriteNibble(num_lines_ptn | dot_format_ptn);

 //The rest of the init is not specific to 4-bit mode.
 //NOTE: we're writing full bytes now, not nibbles.

 // display control:
 // turn display on, cursor off, no blinking

 //clear display

 // entry mode set: 06
 // increment automatically, display shift, entire shift off

 delay(1);//TODO: remove unnecessary delays

//non-core stuff --------------------------------------
//move the cursor to the given absolute position.  line numbers start at 1.
//if this is not a 2-line LCD4Bit instance, will always position on first line.
void LCD4Bit::cursorTo(int line_num, int x){
 //first, put cursor home
if (x>19)
switch (line_num)
case 1:
  x+=0x00 ; break;
case 2:
  x+= 0x40 ; break;
case 3:
  x+= 0x14 ; break; // In fact, line 3 is an extension of the line 1 (beyond the 20 first characters)
case 4:
  x+= 0x54 ; break; // Line 4 is an extension of line 2


//scroll whole display to left
void LCD4Bit::leftScroll(int num_chars, int delay_time){
 for (int i=0; i<num_chars; i++) {

//Improvements ------------------------------------------------
//Remove the unnecessary delays (e.g. from the end of pulseEnablePin()).
//Allow the user to pass the pins to be used by the LCD in the constructor, and store them as member variables of the class instance.

and here is the test program:

#include <LCD4Bit.h>
LCD4Bit lcd = LCD4Bit(4);

void setup() {
pinMode(13, OUTPUT);  //we'll use the debug LED to output a heartbeat

void loop() {  
digitalWrite(13, HIGH);  //light the debug LED
lcd.printIn("Line 1");
lcd.printIn("Line 2");
lcd.printIn("Line 3");
lcd.printIn("Line 4");
digitalWrite(13, LOW);  //clear the debug LED

Any help in this would be sooo great!!!


Anyone has a valid link to Jonathan's modified LCD4bit library for 20x4 LCD? none of the original links work and not even the ones on the arduino website or playground site.

Thanks! The other ones use 2 enable pins, which is not what i have.

Thanks again, Benny



like benedetoula i am searching for a valid link to the modified LCD4bit library.

I own a 20x2 Datavision DV-20208 and with the standard LCD4bit library i only got the first row working.

Is there a chance to get the modified library? Please post it or send it via PN.

Big thx


Go with the LiquidCrystal library. Its much better and has better overall support for all the features the Hitachi based LCDs have.


Apr 10, 2010, 10:26 pm Last Edit: Apr 11, 2010, 02:05 pm by bingo2000 Reason: 1
Has someone edited the new "LiquidCrystal library" to use 2 enables pins, for two chips on one LCD???

It has been done!! And works!


Hi Guys,

Big thanks to people for creating this library. I have a 20x4 LCD which is working fine with the mods mem suggested.

The only problem is that when I try and integrate the LCD functions in to another sketch I have been working on the text garbles and prints in random locations.

The sketch that I am integrating in to features a DS1307 I2C so uses the wire library. Could that effect the results?



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