ESP8266 - RTC

This tutorial instructs you how to use ESP8266 to read date and time from RTC module. In detail, we will learn:

How to connect DS3231 Real-Time Clock module to ESP8266.
How to program ESP8266 to read date and time (second, minute, hour, day of week, day off month, month, and year) from the DS3231 RTC module.
How to program ESP8266 to create daily schedules.
How to program ESP8266 to create weekly schedules.
How to program ESP8266 to create schedules on a specific date.

Hardware Preparation

1	×	ESP8266 NodeMCU
1	×	Micro USB Cable
1	×	Real-Time Clock DS3231 Module
1	×	CR2032 battery
1	×	Jumper Wires
1	×	Breadboard
1	×	(Optional) 5V Power Adapter for ESP8266
1	×	(Optional) Screw Terminal Expansion Board for ESP8266

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables.

Overview of Real-Time Clock DS3231 Module

ESP8266 has certain functions related to time, such as millis() and micros(). However, they do not provide the date and time (seconds, minutes, hours, day, date, month, and year). To get this information, we need to use a Real-Time Clock (RTC) module, such as DS3231 or DS1370. The DS3231 Module has greater precision than the DS1370. For more information, please see DS3231 vs DS1307.

The RTC Module Pinout

The Real-Time Clock DS3231 Module has 10 pins:

32K: This pin provides a stable and precise reference clock.
SQW: This pin produces a square wave at 1Hz, 4kHz, 8kHz or 32kHz and can be managed through programming. It can also be used as an alarm interrupt in various time-dependent applications.
SCL: This is the serial clock pin for the I2C interface.
SDA: This is the serial data pin for the I2C interface.
VCC: This pin supplies power to the module. It can be between 3.3V and 5.5V.
GND: This is the ground pin.

For regular operation, four pins are required: VCC, GND, SDA, and SCL.

The DS3231 Module has a battery holder that, when a CR2032 battery is inserted, will keep the time on the module running even when the main power is off. Without the battery, the time information will be lost if the main power is disconnected and it will need to be reset.

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

See more in ESP8266's pinout and how to supply power to the ESP8266 and other components.

ESP8266 - DS3231 RTC Module

DS3231 RTC Module	ESP8266
Vin	3.3V
GND	GND
SDA	GPIO4
SCL	GPIO5

How To Program For DS3231 RTC Module

Include the library.

#include <RTClib.h>

Create a RTC object:

RTC_DS3231 rtc;

Begin the RTC setup process.

if (! rtc.begin()) { Serial.println("Couldn't find RTC"); while (1); }

Set the RTC to the date and time on the computer when the sketch was compiled for the initial time.

rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));

Retrieves date and time data from the RTC module.

DateTime now = rtc.now(); Serial.print("Date & Time: "); Serial.print(now.year(), DEC); Serial.print('/'); Serial.print(now.month(), DEC); Serial.print('/'); Serial.print(now.day(), DEC); Serial.print(" ("); Serial.print(now.dayOfTheWeek()); Serial.print(") "); Serial.print(now.hour(), DEC); Serial.print(':'); Serial.print(now.minute(), DEC); Serial.print(':'); Serial.println(now.second(), DEC);

ESP8266 Code – How to get data and time

Detailed Instructions

To get started with ESP8266 on Arduino IDE, follow these steps:

Check out the how to setup environment for ESP8266 on Arduino IDE tutorial if this is your first time using ESP8266.
Wire the components as shown in the diagram.
Connect the ESP8266 board to your computer using a USB cable.
Open Arduino IDE on your computer.
Choose the correct ESP8266 board, such as (e.g. NodeMCU 1.0 (ESP-12E Module)), and its respective COM port.
Click to the Libraries icon on the left bar of the Arduino IDE.
Search for “RTClib” and locate the RTC library by Adafruit.
Press the Install button to install the RTC library.

Copy the code and open it with the Arduino IDE.
Click the Upload button in the IDE to send it to the ESP8266.
Open the Serial Monitor.
Check the output on the Serial Monitor.

COM6

Send

Date & Time: 2021/10/6 (Wednesday) 11:27:35 Date & Time: 2021/10/6 (Wednesday) 11:27:36 Date & Time: 2021/10/6 (Wednesday) 11:27:37 Date & Time: 2021/10/6 (Wednesday) 11:27:38 Date & Time: 2021/10/6 (Wednesday) 11:27:39 Date & Time: 2021/10/6 (Wednesday) 11:27:40 Date & Time: 2021/10/6 (Wednesday) 11:27:41 Date & Time: 2021/10/6 (Wednesday) 11:27:42 Date & Time: 2021/10/6 (Wednesday) 11:27:43 Date & Time: 2021/10/6 (Wednesday) 11:27:44

Autoscroll Show timestamp

Clear output

9600 baud

Newline

ESP8266 Code – How to make daily schedule

/* * This ESP8266 NodeMCU code was developed by newbiely.com * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp8266/esp8266-rtc */ // Date and time functions using a DS3231 RTC connected via I2C and Wire lib #include <RTClib.h> // event from 13:50 to 14:10 uint8_t DAILY_EVENT_START_HH = 13; // event start time: hour uint8_t DAILY_EVENT_START_MM = 50; // event start time: minute uint8_t DAILY_EVENT_END_HH = 14; // event end time: hour uint8_t DAILY_EVENT_END_MM = 10; // event end time: minute RTC_DS3231 rtc; char daysOfTheWeek[7][12] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }; void setup () { Serial.begin(9600); // SETUP RTC MODULE if (! rtc.begin()) { Serial.println("Couldn't find RTC"); while (1); } // sets the RTC to the date & time on PC this sketch was compiled rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); // sets the RTC with an explicit date & time, for example to set // January 21, 2021 at 3am you would call: // rtc.adjust(DateTime(2021, 1, 21, 3, 0, 0)); } void loop () { DateTime now = rtc.now(); if (now.hour() >= DAILY_EVENT_START_HH && now.minute() >= DAILY_EVENT_START_MM && now.hour() < DAILY_EVENT_END_HH && now.minute() < DAILY_EVENT_END_MM) { Serial.println("It is on scheduled time"); // TODO: write your code" } else { Serial.println("It is NOT on scheduled time"); } printTime(now); } void printTime(DateTime time) { Serial.print("TIME: "); Serial.print(time.year(), DEC); Serial.print('/'); Serial.print(time.month(), DEC); Serial.print('/'); Serial.print(time.day(), DEC); Serial.print(" ("); Serial.print(daysOfTheWeek[time.dayOfTheWeek()]); Serial.print(") "); Serial.print(time.hour(), DEC); Serial.print(':'); Serial.print(time.minute(), DEC); Serial.print(':'); Serial.println(time.second(), DEC); }

ESP8266 Code – How to make weekly schedule

/* * This ESP8266 NodeMCU code was developed by newbiely.com * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp8266/esp8266-rtc */ // Date and time functions using a DS3231 RTC connected via I2C and Wire lib #include <RTClib.h> // UNCHANGABLE PARAMATERS #define SUNDAY 0 #define MONDAY 1 #define TUESDAY 2 #define WEDNESDAY 3 #define THURSDAY 4 #define FRIDAY 5 #define SATURDAY 6 // event on Monday, from 13:50 to 14:10 uint8_t WEEKLY_EVENT_DAY = MONDAY; uint8_t WEEKLY_EVENT_START_HH = 13; // event start time: hour uint8_t WEEKLY_EVENT_START_MM = 50; // event start time: minute uint8_t WEEKLY_EVENT_END_HH = 14; // event end time: hour uint8_t WEEKLY_EVENT_END_MM = 10; // event end time: minute RTC_DS3231 rtc; char daysOfTheWeek[7][12] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }; void setup () { Serial.begin(9600); // SETUP RTC MODULE if (! rtc.begin()) { Serial.println("Couldn't find RTC"); while (1); } // sets the RTC to the date & time on PC this sketch was compiled rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); // sets the RTC with an explicit date & time, for example to set // January 21, 2021 at 3am you would call: // rtc.adjust(DateTime(2021, 1, 21, 3, 0, 0)); } void loop () { DateTime now = rtc.now(); if (now.dayOfTheWeek() == WEEKLY_EVENT_DAY && now.hour() >= WEEKLY_EVENT_START_HH && now.minute() >= WEEKLY_EVENT_START_MM && now.hour() < WEEKLY_EVENT_END_HH && now.minute() < WEEKLY_EVENT_END_MM) { Serial.println("It is on scheduled time"); // TODO: write your code" } else { Serial.println("It is NOT on scheduled time"); } printTime(now); } void printTime(DateTime time) { Serial.print("TIME: "); Serial.print(time.year(), DEC); Serial.print('/'); Serial.print(time.month(), DEC); Serial.print('/'); Serial.print(time.day(), DEC); Serial.print(" ("); Serial.print(daysOfTheWeek[time.dayOfTheWeek()]); Serial.print(") "); Serial.print(time.hour(), DEC); Serial.print(':'); Serial.print(time.minute(), DEC); Serial.print(':'); Serial.println(time.second(), DEC); }

ESP8266 Code – How to make schedule on speficic date

/* * This ESP8266 NodeMCU code was developed by newbiely.com * * This ESP8266 NodeMCU code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp8266/esp8266-rtc */ // Date and time functions using a DS3231 RTC connected via I2C and Wire lib #include <RTClib.h> // UNCHANGABLE PARAMATERS #define SUNDAY 0 #define MONDAY 1 #define TUESDAY 2 #define WEDNESDAY 3 #define THURSDAY 4 #define FRIDAY 5 #define SATURDAY 6 #define JANUARY 1 #define FEBRUARY 2 #define MARCH 3 #define APRIL 4 #define MAY 5 #define JUNE 6 #define JULY 7 #define AUGUST 8 #define SEPTEMBER 9 #define OCTOBER 10 #define NOVEMBER 11 #define DECEMBER 12 // event from 13:50 August 15, 2021 to 14:10 September 29, 2021 DateTime EVENT_START(2021, AUGUST, 15, 13, 50); DateTime EVENT_END(2021, SEPTEMBER, 29, 14, 10); RTC_DS3231 rtc; char daysOfTheWeek[7][12] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }; void setup () { Serial.begin(9600); // SETUP RTC MODULE if (! rtc.begin()) { Serial.println("Couldn't find RTC"); Serial.flush(); while (1); } // sets the RTC to the date & time on PC this sketch was compiled rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); // sets the RTC with an explicit date & time, for example to set // January 21, 2021 at 3am you would call: // rtc.adjust(DateTime(2021, 1, 21, 3, 0, 0)); } void loop () { DateTime now = rtc.now(); if (now.secondstime() >= EVENT_START.secondstime() && now.secondstime() < EVENT_END.secondstime()) { Serial.println("It is on scheduled time"); // TODO: write your code" } else { Serial.println("It is NOT on scheduled time"); } printTime(now); } void printTime(DateTime time) { Serial.print("TIME: "); Serial.print(time.year(), DEC); Serial.print('/'); Serial.print(time.month(), DEC); Serial.print('/'); Serial.print(time.day(), DEC); Serial.print(" ("); Serial.print(daysOfTheWeek[time.dayOfTheWeek()]); Serial.print(") "); Serial.print(time.hour(), DEC); Serial.print(':'); Serial.print(time.minute(), DEC); Serial.print(':'); Serial.println(time.second(), DEC); }

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