High-precision timekeeping in a tiny footprint. This mini DS3231 module puts a temperature-compensated DS3231SN real-time clock on an ultra-compact board — just ~2.7 g — that plugs straight onto a Raspberry Pi's I2C header, and works just as well with Arduino, ESP32 or any I2C microcontroller via jumper wires. It holds time to about ±0.4 seconds a day (±5 ppm across −40 to +85°C) — a couple of minutes a year, versus the minutes-per-week drift of a DS1307. Built-in temperature sensor, two calendar alarms and a 3.3–5.5V supply. Backup battery not included.
- DS3231SN RTC, temperature-compensated
- Accurate to ±5 ppm — about ±0.4 s a day
- 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
What's in the box
Backup battery (rechargeable LIR2032) not included — see the FAQ on battery type.
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.
- Fit a coin cell
Insert a rechargeable LIR2032 so it keeps time when the power is off.
- 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?
Far steadier. The DS3231SN's temperature-compensated crystal holds time to about ±0.4 seconds a day (±5 ppm) — a couple of minutes a year — where a DS1307 can drift minutes per week. If timekeeping matters, this is the one to use.
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?
No. It takes a rechargeable LIR2032 coin cell (not included); the board has a charging circuit to keep it topped up while powered.
Good to know: ultra-compact DS3231SN RTC (RTC-only, no EEPROM), takes a rechargeable LIR2032 backup cell (not included). Every order is checked before it ships from our Te Awamutu stock.