An Arduino library for controlling a standard 1602 LCD module using a 74HC595 shift register. This library allows you to display text on the LCD using only 3 Arduino pins (data, clock, latch), freeing up valuable I/O.

This library drives a 1602 (or compatible) character LCD by sending 4-bit data through a 74HC595 shift register. It minimizes pin usage by shifting out the required bits over SPI-style control.

• Minimal wiring — uses only 3 Arduino pins
• Supports standard 1602 LCD commands
• Simple API: begin(), clear(), print(), command()
• Easily expandable (setCursor, createChar, etc.)

• Arduino-compatible board (Nano, Uno, Mega, etc.)
• 1602 LCD module (HD44780-compatible)
• 74HC595 shift register
• Arduino IDE

Arduino → 595 connections:

• Data → Arduino pin X (pin 2)

• Clock → Arduino pin Y (pin 4)

• Latch → Arduino pin Z (pin 3)

• Replace X, Y, Z with your actual pin numbers when initializing.

1. Download this repo as .zip or clone via Git:

   git clone https://github.com/llcesselx/LCD595.git
   

According to 1602 LCD Module Datasheets, the initialization sequence recommends giving the LCD at least 40 ms to start up, when the LCD starts up, it starts in 8-bit mode by default. We are only using 4 data pins and want to start the LCD in 4-bit mode. We have to do this manually.

Sending the nibble 0x03 sends the bits 0011 to the LCD three times to ensure the LCD is fully reset. When we send the fourth nibble 0x02, we are sending the bits 0010 which sets it to 4-bit mode. Every program has to start with (your object name here).begin();

#include <lcd595.h>

LCD595 lcd(2, 4, 3);

void setup() {
    lcd.begin();
    lcd.print("Hello, world!");
}

void loop() {}

1. First we have to instruct the compliler to include the contents of lcd595.h whcih contains the class definition for LCD595, without this the compiler will not recognize LCD595 as a valid type.

#include <lcd595.h>

2. This line instantiates an object of teh LCD595 class and names it lcd. The class constructor LCD595::LCD595(uint8_t dataPin, uint8_t clockPin, uint8_t latchPin) is invoked with the arguments 2, 4, and 3. These values initialize the private member variables _dataPin, _clockPin, and _latchPin within the lcd object. The object, lcd, now encapsulates the states and methods required for all the following hardware interactions.

LCD595 lcd(2, 4, 3);

3. This line calls the begin() member function on the object we named lcd. This function handles low-level hardware and controller initialization. It uses the arduino's built-in pinMode() function that sets the data, clock, and latch pins as OUTPUT.

lcd.begin();

4. The print method passes a string literal (const char*), which the method then iterates through each character in the character array until it reaches a \0 null terminator. For each character, the method invokes the write() method. The write() method sends the characters's 8 bit ASCII value by setting the RS (Register Select) pin to high and then sending the high and low nibbles of the byte to the display.

lcd.print("Hello, world!");