You can use a DS1307 with an ESP8266 for timekeeping, 56 bytes of battery-backed general-purpose SRAM, and a programmable square-wave signal. In an Arduino sketch, choose I²C pins for your specific ESP8266 board with Wire.begin(SDA, SCL). For the DS1307’s open-drain SQW/OUT pin, use a pull-up voltage that is safe for the ESP8266 input—do not pull it up to 5 V.
What the DS1307 adds to an ESP8266 project
The DS1307 is an I²C real-time clock/calendar. It keeps time with a 32.768 kHz crystal and has a separate backup supply input so the clock can continue when the main supply is absent. It also includes 56 bytes of battery-backed general-purpose SRAM; Analog Devices describes the RAM as supporting unlimited writes. See the DS1307 product information and the Rev. 5 datasheet, dated March 23, 2015.
Those features serve distinct purposes: the clock/calendar maintains date and time, the SRAM stores small amounts of data across loss of the main supply, and SQW/OUT can supply a timing signal or a static output. A module can package the chip with supporting parts, but module layouts and provisions vary.
Choose I²C pins for your ESP8266 board
The ESP8266 Arduino Core lets a sketch set I²C pins by calling Wire.begin(sda, scl). Its documentation gives GPIO 4 for SDA and GPIO 5 for SCL as defaults, and GPIO 0 for SDA and GPIO 2 for SCL as an ESP-01 example. These are not interchangeable recommendations for every board: check the board’s pin mapping and startup constraints before wiring. Consult the ESP8266 Arduino Core Wire documentation.
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- DS3231 16-pin memory chips - AT24C32 ,extremely accurate I2C real-time clock (RTC), with an integrated temperature-compensated crystal oscillator (TCXO) and crystal.
- Highly accurate RTC completely manages all timekeeping functions.The device incorporates a battery input, disconnect the main power supply and maintains accurate timekeeping.
- Integrated oscillator improve long-term accuracy of the device and reduces the number of components of the production line.
- Provides two configurable alarm clock and a calendar can be set to a square wave output. Address and data are transferred serially through an I2C bidirectional bus.
- A precision temperature-compensated voltage reference and comparator circuit monitors the status of VCC to detect power failures, provide a reset output. In addition, RST pin is monitored as generating a μP reset.
For example, after confirming that GPIO 4 and GPIO 5 are suitable on your board, initialize I²C with:
Wire.begin(4, 5); // SDA, SCLConnect the RTC’s SDA and SCL to those selected pins, and connect the grounds. The exact power and pull-up wiring depends on the particular DS1307 circuit or module; inspect its documentation rather than assuming every board is wired alike.
Rank #2
- DS3231 16-pin memory chips - AT24C32 ,extremely accurate I2C real-time clock (RTC), with an integrated temperature-compensated crystal oscillator (TCXO) and crystal.
- Integrated oscillator improve long-term accuracy of the device and reduces the number of components of the production line.
- Provides two configurable alarm clock and a calendar can be set to a square wave output. Address and data are transferred serially through an I2C bidirectional bus.
- Highly accurate RTC completely manages all timekeeping functions.The device incorporates a battery input, disconnect the main power supply and maintains accurate timekeeping.
- A precision temperature-compensated voltage reference and comparator circuit monitors the status of VCC to detect power failures, provide a reset output. In addition, RST pin is monitored as generating a μP reset.
Wire the DS1307 and protect the ESP8266 input
Bare chip and module differences
A bare DS1307 circuit uses a 32.768 kHz crystal and a separate backup supply input, as specified in the DS1307 datasheet. A module may include some of these supporting components, but do not assume it includes a functioning crystal, pull-ups, a battery, or a particular signal voltage. Check the module’s documentation and inspect its actual connections before applying power.
SQW/OUT pull-up voltage
The DS1307 datasheet specifies SQW/OUT as an open-drain output that requires an external pull-up. Although the datasheet permits a pull-up as high as 5.5 V for the RTC output, that does not make an ESP8266 GPIO 5 V tolerant. Choose a pull-up voltage and resistance compatible with both the RTC circuit and the ESP8266 input; do not connect a 5 V pull-up directly to an ESP8266 GPIO. Check the Espressif ESP8266EX datasheet for host-chip electrical specifications.
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Rank #3
- 【Product】DS1307 I2C real time clock chip, 24C32 32K I2C EEPROM memory, the DS1307 is accessed via the I2C protocol.
- 【Advantage】Solve the problem DS1307 with backup battery can not read and write, In battery backup mode, Low power consumption, Automatic brownout detection and switching circuit.
- 【Feature】It can count seconds, hours, minutes, days of the month, months, and days of the week, and has the function of leap year compensation. Yearbook Online 2100.
- 【Multi-function】Connected to the clock pin of DS1307 to provide clock signal for microcontroller. Can be cascaded to other I2C devices.
- 【Note】Using 2032 rechargeable lithium battery, And with charging circuit. After fully charged, it can provide DS1307 timing for 1 year. Note:This product kit does not come with a battery.
Configure the square-wave output
The DS1307 provides four selectable square-wave frequencies: 1 Hz, 4 kHz, 8 kHz, and 32 kHz. When square-wave output is disabled, the control behavior also allows the pin to act as a static output. The available setting therefore depends on whether your project needs a periodic signal or a fixed output. The details are in the DS1307 datasheet; the Adafruit RTClib SQW example illustrates off, constant-on, and the four square-wave modes.
Driver APIs differ, so follow the library you selected rather than assuming a particular call or enum name. For example, the esp-idf-lib DS1307 driver documentation describes functions for configuring the output mode and frequency.
Rank #4
- Two wire I2C interface ⊙Hour : Minutes : Seconds AM/PM ⊙Day Month, Date - Year ⊙Size: 28x25x10mm ⊙Leap year compensation ⊙Accurate calendar up to year 2100 ⊙DS1307 based RTC with LIR2032 battery (Battery include) ⊙1Hz output pin ⊙56 Bytes of Non-volatile memory available to user ⊙The module comes fully assembled and pre-programmed with the current time. ⊙This is the DS1307 Real Time Clock Module For Arduino AVR ARM PIC. ⊙The DS1307 is accessed via the I2C protocol.
- This is the DS1307 Real Time Clock developed by one of our designer waiman. The module comes fully assembled and pre-programmed with the current time (ok, so it's our current time - MST). The included Lithium coin cell battery (CR1225 41mAh) will run the module for a minimum of 9 years (17 years typical) without external 5V power. The DS1307 is accessed via the I2C protocol.
- Package included：Ximimark 5Pcs I2C RTC DS1307 AT24C32 Real Time Clock Module for AVR ARM PIC SMD for Arduino
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Use the 56-byte SRAM for small persistent values
The DS1307’s battery-backed RAM is general-purpose storage, not a guarantee that an application’s saved data is valid or internally consistent. The esp-idf-lib driver documents byte-range access at offsets 0 through 55. Keep your data within that range and define your own layout—for example, reserve bytes for a format version and validation value alongside the data. Those checks are application design choices; the DS1307 does not prescribe a storage format.
Because the RAM is small, it suits compact settings or state rather than large logs. The manufacturer documents 56 bytes and unlimited writes in its product information; the driver’s RAM documentation describes the usable offsets.
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Best Value
- DS3231 16-pin memory chips - AT24C32 ,extremely accurate I2C real-time clock (RTC), with an integrated temperature-compensated crystal oscillator (TCXO) and crystal.
- Integrated oscillator improve long-term accuracy of the device and reduces the number of components of the production line.
- Provides two configurable alarm clock and a calendar can be set to a square wave output. Address and data are transferred serially through an I2C bidirectional bus.
- Highly accurate RTC completely manages all timekeeping functions.The device incorporates a battery input, disconnect the main power supply and maintains accurate timekeeping.
- A precision temperature-compensated voltage reference and comparator circuit monitors the status of VCC to detect power failures, provide a reset output. In addition, RST pin is monitored as generating a μP reset.
Check these details before choosing or wiring hardware
- ESP8266 board: Confirm the available SDA/SCL pins and any boot-time restrictions for those GPIOs.
- RTC construction: Establish whether you have a bare chip or a module, and whether the required crystal and backup supply are present.
- Pull-ups: Determine whether the I²C lines and SQW/OUT already have pull-ups, what voltage they use, and whether that voltage is safe for the ESP8266.
- Module features: Verify that a battery is included and usable, and that SQW/OUT is exposed if your project needs it.
- Output requirement: Choose a supported frequency or static output mode that matches the circuit’s purpose.
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