DS3231 / AT24C32 Real-Time Clock (RTC)

// Requires the esp-idf-lib DS3231 driver from the ESP Component Registry:
//   idf.py add-dependency "esp-idf-lib/ds3231^1.1.7"

#include <stdio.h>
#include <string.h>
#include <time.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "ds3231.h"

#define SDA_GPIO GPIO_NUM_21
#define SCL_GPIO GPIO_NUM_22

void app_main(void)
{
    ESP_ERROR_CHECK(i2cdev_init());

    i2c_dev_t dev;
    memset(&dev, 0, sizeof(i2c_dev_t));
    ESP_ERROR_CHECK(ds3231_init_desc(&dev, 0, SDA_GPIO, SCL_GPIO));

    while (1) {
        struct tm time;
        float temperature;
        if (ds3231_get_time(&dev, &time) == ESP_OK && ds3231_get_temp_float(&dev, &temperature) == ESP_OK)
            printf("%04d-%02d-%02d %02d:%02d:%02d, chip temp %.2f C\n",
                   time.tm_year + 1900, time.tm_mon + 1, time.tm_mday,
                   time.tm_hour, time.tm_min, time.tm_sec, temperature);
        else
            printf("Could not read time from RTC\n");
        vTaskDelay(pdMS_TO_TICKS(1000));
    }
}

i2c:
  sda: GPIO21
  scl: GPIO22

time:
  - platform: ds1307
    id: rtc_time  # the DS3231 is register-compatible with the ds1307 platform

text_sensor:
  - platform: template
    name: "DS3231 Date and Time"
    lambda: |-
      char buf[20];
      auto now = id(rtc_time).now();
      if (!now.is_valid()) return {"unknown"};
      now.strftime(buf, sizeof(buf), "%Y-%m-%d %H:%M:%S");
      return {buf};
    update_interval: 1s

[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
lib_deps =
    adafruit/RTClib @ ^2.1.4

#include <Arduino.h>
#include <Wire.h>
#include <RTClib.h>

RTC_DS3231 rtc;

void setup() {
    Serial.begin(9600);
    Wire.begin();
    if (!rtc.begin()) {
        Serial.println("Couldn't find RTC");
        while (1);
    }
    if (rtc.lostPower()) {
        rtc.adjust(DateTime(2023, 12, 4, 14, 30, 0)); // Set initial date/time
    }
}

void loop() {
    DateTime now = rtc.now();
    Serial.print("Time: ");
    Serial.print(now.hour());
    Serial.print(":");
    Serial.print(now.minute());
    Serial.print(":");
    Serial.println(now.second());
    Serial.print("Date: ");
    Serial.print(now.year());
    Serial.print("/");
    Serial.print(now.month());
    Serial.print("/");
    Serial.println(now.day());
    delay(1000);
}

from machine import I2C, Pin
import time

# DS3231 I2C address
DS3231_ADDRESS = 0x68

def bcd_to_decimal(bcd):
    return (bcd >> 4) * 10 + (bcd & 0x0F)

def decimal_to_bcd(decimal):
    return ((decimal // 10) << 4) | (decimal % 10)

def set_time(i2c, year, month, day, hour, minute, second):
    data = [decimal_to_bcd(second), decimal_to_bcd(minute), decimal_to_bcd(hour),
            decimal_to_bcd(day), 0, decimal_to_bcd(month), decimal_to_bcd(year - 2000)]
    i2c.writeto_mem(DS3231_ADDRESS, 0x00, bytes(data))

def get_time(i2c):
    data = i2c.readfrom_mem(DS3231_ADDRESS, 0x00, 7)
    second = bcd_to_decimal(data[0])
    minute = bcd_to_decimal(data[1])
    hour = bcd_to_decimal(data[2])
    day = bcd_to_decimal(data[4])
    month = bcd_to_decimal(data[5] & 0x1F)
    year = bcd_to_decimal(data[6]) + 2000
    return year, month, day, hour, minute, second

# Initialize I2C
i2c = I2C(0, scl=Pin(22), sda=Pin(21))

# Set initial time
set_time(i2c, 2023, 12, 4, 14, 30, 0)

# Loop to read time
while True:
    year, month, day, hour, minute, second = get_time(i2c)
    print(f"Time: {hour:02}:{minute:02}:{second:02}, Date: {year:04}/{month:02}/{day:02}")
    time.sleep(1)