STM32 RTC LCD Display

Project Overview

This project demonstrates how to use the internal Real-Time Clock (RTC) of an STM32F7 microcontroller to display the current time and date on a 16×2 I²C LCD. By using the PCF8574 I²C backpack, the project reduces GPIO usage to just SDA and SCL, making the setup compact and easy to integrate.

Key features include:

• Initializing the STM32 internal RTC
• Displaying real-time time (HH:MM:SS) and date (DD-MM-YYYY) on a 16×2 LCD
• Using RTC backup registers to retain time after resets
• Optional alarm setup using RTC Alarm A

This project is ideal for beginners exploring STM32 HAL, I²C, and RTC modules, and serves as a foundation for embedded clocks, timers, and real-time displays.

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Features

• Real-time time and date display on a 16×2 LCD
• I²C communication using STM32 HAL (hi2c1)
• RTC backup register to preserve time on resets
• Configurable RTC Alarm A
• Minimal pin usage (SDA + SCL only)

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Hardware Requirements

Component	Specification / Pin	Notes
STM32F7xx development board	e.g., Nucleo F767	—
16×2 LCD with I²C backpack	PCF8574	—
Jumper wires	—	—
LCD Power Supply	5V	LCD requires 5V

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Wiring

LCD Pin	STM32 Pin	Notes
GND	GND	Ground
VCC	5V	LCD requires 5V
SDA	PB7 (I2C1)	I²C data line
SCL	PB6 (I2C1)	I²C clock line

Tip: Adjust the onboard contrast potentiometer to make text visible.

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Code Overview

RTC Initialization & Backup Check

if(HAL_RTCEx_BKUPRead(&hrtc, RTC_BKP_DR1) != 0x32F2)
{
    set_time(); // Set initial time if backup register is empty
}

Time & Date Retrieval

RTC_DateTypeDef gDate;
RTC_TimeTypeDef gTime;

HAL_RTC_GetTime(&hrtc, &gTime, RTC_FORMAT_BIN);
HAL_RTC_GetDate(&hrtc, &gDate, RTC_FORMAT_BIN);

sprintf(time,"%02d:%02d:%02d", gTime.Hours, gTime.Minutes, gTime.Seconds);
sprintf(date,"%02d-%02d-%d", gDate.Date, gDate.Month, 2026 + gDate.Year);

Display on LCD

lcd_send_cmd(0x80); // Line 1
lcd_send_string(time);
lcd_send_cmd(0xC0); // Line 2
lcd_send_string(date);

Alarm Setup (Optional)

set_alarm(); // Uses RTC Alarm A

Main Loop

while (1)
{
    get_time();
    display_time();
    HAL_Delay(500); // Update every 500ms
}

Example Display Output

Line 1: 20:44:50
Line 2: 27-01-2026

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References

This project was implemented using concepts explained on the ControllersTech YouTube channel.

Used as a learning reference for STM32 RTC configuration, I²C LCD interfacing, and HAL usage.

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Author

Developed as part of hands-on learning in Embedded Systems and STM32 Microcontroller Programming.