High-precision timekeeping in a tiny footprint. This mini DS3231 module uses a temperature-compensated DS3231 real-time clock and plugs onto a Raspberry Pi I2C header. It also works with Arduino, ESP32 and other I2C controllers. The fitted CR927-format 3 V backup cell keeps time when main power is off.
- DS3231SN RTC, temperature-compensated
- ±2 ppm from 0 to +40°C; ±3.5 ppm from -40 to +85°C
- Far steadier timekeeping than a DS1307
- Built-in digital temperature sensor (±3°C)
- Two programmable calendar alarms
- 1 Hz & 32.768 kHz outputs
- 3.3–5.5V supply, low power
- Ultra-compact (~2.7 g), plugs onto Raspberry Pi
Specifications
Datasheets
What's in the box
Includes the fitted CR927-format backup cell shown on the module.
Great for
Getting started
- Connect it
On a Pi, push it onto the first GPIO header pins so + D C NC − line up. On any MCU, wire +→3.3–5V, D→SDA, C→SCL, −→GND.
- Check the fitted cell
The small CR927-format backup cell is already installed. Do not fit a 20 mm coin cell.
- Enable / add a library
On Pi, enable I2C and the DS3231 overlay; on Arduino, use RTClib (DS3231).
- Set the time
Set it once — it then keeps accurate time on its own.
Common questions
How accurate is it versus a DS1307?
The DS3231 is temperature compensated and specified to ±2 ppm from 0 to +40°C and ±3.5 ppm from -40 to +85°C. That is much steadier than a typical DS1307 module.
Does it only work with Raspberry Pi?
No — it's labelled "for Pi" because it plugs neatly onto the Pi's I2C header, but it's a standard I2C device. Wire + D C − to VCC / SDA / SCL / GND and it works with Arduino, ESP32 or any microcontroller (3.3–5.5V).
What do the pins mean?
+ = VCC (3.3–5.5V), D = SDA (data), C = SCL (clock), NC = not connected, − = GND.
Does it have onboard EEPROM?
No — this compact version is RTC-only (no AT24C32 EEPROM, unlike the larger ZS-042 board). If you need extra storage, add a separate EEPROM or use your microcontroller's memory.
Is the battery included?
Yes. This compact board has a fitted CR927-format 3 V backup cell. It does not use a LIR2032 cell or a 20 mm holder.
Note: This compact module is RTC-only with no onboard EEPROM. The NC pin is not connected.