3 wires interface for LCD display
This post is based on the work made previously by tomek in wiring LCD displays using 4 bits. The basic idea is to group the 7 pins that are needed to drive the LCD in only 3 using a shift register. This is a cheap alternative to serial LCDs.
Figure 1: schematic by Philip Warner
The schematic shows that wiring the LCD is a simple operation. It has been drawn in a way that makes it possible to develop this as part of a single sided PCB including a variable resistor to control the LCD's contrast. Note that the pin-out of the LCD module may differ slightly from the pin-out depicted; some LCD modules have pins 15 and 16 on the left side, before pin 1.
Figure 2: wiring the components
In this picture we see the actual connections on a breadboard. Everything runs on the power from the USB powered board. The code below includes a couple of functions that will print integer numbers to the LCD, as well as single characters.
Also available is a library: Attach:LCD3WireLibrary.zip. To remain command-compatible with the LCD4BitLibrary, this library does not contain the number-formatting code which is included in the code below.
/* LCD display with 3 wires
* ------------------------
*
* based on previous examples by Tomek.
* This program will use shiftout to send
* data to a shift register with strobe that
* will transfer the serial into parallel data
*
* the pin-out for LCD displays is standard and there is plenty
* of documentation to be found on the internet.
*
* (cleft) 2007 Dojodave for K3 and SADI
* http://www.arduino.cc
*
*/
// pins to be used on Arduino
int led = 13;
int count = 0;
int Dout = 11;
int STR = 12;
int CLK = 10;
// the Qx in the order they are connected on the chip
int DI = 1;
int RW = 2;
int Enable = 3;
int DB[] = {
7, 6, 5, 4};
void LcdInit() {
delay(100);
// initialize LCD after a short pause
// needed by the LCD's controller
/////////// 4 pin initialization
LcdCommandWrite(0x03); // function set:
// 4 pin initialization
delay(64);
LcdCommandWrite(0x03); // function set:
// 4 pin initialization
delay(50);
LcdCommandWrite(0x03); // function set:
// 4 pin initialization
delay(50);
LcdCommandWrite(0x02); // function set:
// 4 pin initialization
delay(50);
LcdCommandWrite(0x2C); // function set:
// 4-bit interface, 1 display lines, 5x7 font
/////////// end of 4 pin initialization
delay(20);
LcdCommandWrite(0x06); // entry mode set:
// increment automatically, no display shift
delay(20);
LcdCommandWrite(0x0E); // display control:
// turn display on, cursor on, no blinking
delay(20);
// clear display, set cursor position to zero
LcdCommandWrite(0x01);
delay(100);
LcdCommandWrite(0x80); // display control:
delay(20);
}
void sendByteOut(int value) {
shiftOut(Dout, CLK, LSBFIRST, value);
digitalWrite(STR, HIGH);
delayMicroseconds(10);
digitalWrite(STR,LOW);
}
void LcdCommandWrite(int value) {
int i = 0;
int value1 = 0;
int control = 0; // stores DI and RW
digitalWrite(STR,LOW); // set the strobe LOW
control = value >> 8; // get the control signals DI and RW
control <<= 5; // shift the control signals to the left
value1 = value;
value1 >>= 4; //send the first 4 databits (from 8)
value1 |= control; // set the control values
value1 &= 239; // set Enable LOW
sendByteOut(value1);
value1 |= 16; // Set Enable HIGH
sendByteOut(value1);
value1 &= 239; // set Enable LOW
sendByteOut(value1);
delay(1);
value &= 15; // set HByte to zero
value |= control; // set the control values
value &= 239; // set Enable LOW
sendByteOut(value);
value |= 16; // Set Enable HIGH
sendByteOut(value);
value &= 239; // set Enable LOW
sendByteOut(value);
}
void LcdDataWrite(int value) {
int i = 0;
int value1 = 0;
digitalWrite(STR,LOW); // set the strobe LOW
value1 =value;
value1 >>= 4; //send the first 4 databits (from 8)
value1 |= 64; // set DI HIGH
value1 &= 223; // set RW LOW
value1 &= 239; // set Enable LOW
sendByteOut(value1);
value1 |= 16; // Set Enable HIGH
sendByteOut(value1);
value1 &= 239; // set Enable LOW
sendByteOut(value1);
delay(1);
value &= 15; // set HByte to zero
value |= 64; // set DI HIGH
value &= 223; // set RW LOW
value &= 239; // set Enable LOW
sendByteOut(value);
value |= 16; // Set Enable HIGH
sendByteOut(value);
value &= 239; // set Enable LOW
sendByteOut(value);
}
// efficient way of multiplying numbers by themselves
int pow(int base, int expo) {
int temp = 1;
for (int c = 1; c <= expo; c++) {
temp *= base;
}
return temp;
}
// checks out how many digits there are in a number
int estimateDigits(int nr) {
int dec = 10;
int temp = 1;
int div = nr/dec;
while (div > 0) {
dec *= 10;
div = nr/dec;
temp++;
}
return temp;
}
// shows numbers on the display
void LcdNumberWrite(int nr) {
int digits = estimateDigits(nr);
LcdNumberWrite(nr, digits);
}
// this function help us to write numbers
// with more than one digit
void LcdNumberWrite(int nr, int digits) {
for (int i = digits-1; i >= 0; i--) {
int dec = pow(10,i);
int div = nr/dec;
LcdDataWrite(div+48);
if (div > 0) {
nr -= div*dec;
}
}
}
void setup (void) {
int i = 0;
for (i=CLK; i <= STR; i++) {
pinMode(i,OUTPUT);
}
LcdInit();
LcdCommandWrite(0x0F); // cursor blink
delay(10);
}
void loop (void) {
LcdCommandWrite(0x02); // set cursor position to zero
delay(10);
// Write the message
//like this
LcdDataWrite('L');
LcdDataWrite('c');
LcdDataWrite('d');
//or like this
int wrote[] = {
'D', 'i', 's', 'p', 'l', 'a', 'y', ' ' };
for ( count = 0; count<=7; count++) {
LcdDataWrite(wrote[count]);
}
LcdDataWrite('w');
LcdDataWrite('i');
LcdDataWrite('t');
LcdDataWrite('h');
LcdDataWrite(' ');
// and Numbers over 9 easily like this
LcdNumberWrite(3);
LcdDataWrite(' ');
LcdDataWrite('P');
LcdDataWrite('i');
LcdDataWrite('n');
LcdDataWrite('s');
delay(3000);
}
TODO
- migrate all the commands to a library format --> 20080310 library by Aldo Hoeben
- redo the
schematics andpictures --> 20080310 new schematic by Philip Warner
HISTORY
- old schematic LCD3wiresSchematic.jpg
For more information write to: d.cuartielles [at] arduino.cc