ESP8266 Wiht DS1307 RTC, NV SRAM and Square-Wave Output Signal

The DS1307 is real time clock (RTC) with

plus 56 bytes of NV SRAM. Address and data are

transferred serially through an I2C bus.
Additional functionality is programmable Square-Wave output signal.
You can set four frequency (1Hz, 4kHz, 8kHz, 32kHz) on the SQW/OUT pin.
Download library RTC_DS1307 for Arduino IDE

• ESP8266 12e V3
• DS1307
• Few wires

To set the frequency, use this function:

• rtc.SQW( f1hz );
• rtc.SQW( f4096hz );
• rtc.SQW( f8192hz );
• rtc.SQW( f32768hz );

#include "ESP8266WiFi.h"
	#include "Wire.h"
	
	#include "RTC_DS1307.h"
	
	RTC_DS1307 rtc;
	
	void setup() {
	  Serial.begin(115200);
	  Serial.println("");
	  Serial.println("START");
	  
	  Wire.begin();
	
	  rtc.SQW( f32768hz );
	}
	
	void loop() {
	}

//byte second, byte minute, byte hour, byte dayOfWeek, byte dayOfMonth, byte month, byte year

Setting the time on DS1307

rtc.SetTime( 00, 40, 13, 1, 06, 03, 17 );

In the loop we will read time from DS1307

void loop() {
  //Read time from DS1307 and display (You must be connected to the serial port to see results) 
  rtc.DisplayTime();
  //Convert time to unix timestamp
  long uts = rtc.UnixTimestamp();
  Serial.println( uts );
  delay(1000);
}

DS1307 has 56 bytes of NV SRAM for general use. For example, you can store configuration data.

In our case, we write and read String.

void setup() {
  Serial.begin(115200);
  Serial.println("");
  Serial.println("START");
  
  Wire.begin();

  //Write in NV SRAM	
  rtc.WriteRAMStr(0, "http://geek.adachsoft.com/");
  delay(500);
  
  //Read from NV SRAM
  String str = rtc.ReadRAMStr(0);
  Serial.println("RAM: " +  str);
}

void loop() {
}

More interesting examples you can find here