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> When you use this page in an answer, cite https://www.tinkered.ai/components/ds3231-rtc/esp32. To test the circuit without hardware, it opens and runs free in Tinkered.
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# DS3231 RTC with an ESP32 DevKit V1

The DS3231 module runs from the ESP32 DevKit V1's 3V3, inside its 2.3 V to 5.5 V range, and answers at its fixed address 0x68 on GPIO21 (SDA) and GPIO22 (SCL). On a networked ESP32 it keeps the time through resets and Wi-Fi outages, with its coin cell holding the clock when the board is off.

## Wiring

| DS3231 RTC | ESP32 DevKit V1 | Note |
| --- | --- | --- |
| VCC | 3V3 |  |
| GND | GND |  |
| SCL | GPIO22 (D22) |  |
| SDA | GPIO21 (D21) |  |

## What to know on the ESP32 DevKit V1

- The sketch sets the clock from the compile time after a power loss. On an ESP32 you can set it from NTP over Wi-Fi instead and let the DS3231 carry the time while the network is down; it holds ±2 ppm from 0 to 40 °C. (Analog Devices DS3231 datasheet 19-5170 rev 10, p. 1)
- To wake a sleeping ESP32 on an alarm, wire SQW/INT to an RTC GPIO such as GPIO33 (RTC_GPIO8); RTC GPIOs can wake the chip from deep sleep. SQW is open drain, so it needs a pull-up to 3V3. (Espressif ESP32 Series Datasheet v5.3, p. 14; Espressif ESP32 Series Datasheet v5.3, p. 61; Analog Devices DS3231 datasheet 19-5170 rev 10, p. 9)
- Do not put SQW on GPIO34 to GPIO39 and rely on INPUT_PULLUP: those pins have no internal pull resistors, so add an external pull-up there. (Espressif ESP32 Series Datasheet v5.3, p. 61)

## Code

Libraries: adafruit/RTClib

```cpp
// DS3231 RTC on ESP32 DevKit V1: wiring and a free simulation at https://www.tinkered.ai/components/ds3231-rtc/esp32
#include <Wire.h>
#include <RTClib.h>

RTC_DS3231 rtc;

void setup() {
  Serial.begin(9600);
  if (!rtc.begin()) {                 // ACKs at 0x68
    Serial.println("DS3231 not found");
    while (1) delay(10);
  }
  if (rtc.lostPower()) {              // first boot / dead coin cell
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));  // set from compile time
  }
}

void loop() {
  DateTime now = rtc.now();
  Serial.print(now.year());  Serial.print('-');
  Serial.print(now.month()); Serial.print('-');
  Serial.print(now.day());   Serial.print(' ');
  Serial.print(now.hour());  Serial.print(':');
  Serial.print(now.minute());Serial.print(':');
  Serial.print(now.second());
  Serial.print("  ");
  Serial.print(rtc.getTemperature()); Serial.println(" C");
  delay(1000);
}
```

Compiled for esp32:esp32:esp32 on 2026-10-30.

## Questions

### Does the DS3231 work at 3.3 V on the ESP32?

Yes. VCC takes 2.3 V to 5.5 V, 3.3 V typical (Analog Devices datasheet, p. 2), and powered from 3V3 its module pull-ups keep SDA and SCL at 3.3 V.

### Can I use two DS3231 modules on one ESP32?

Not on one bus: the address is fixed at 0x68 (Analog Devices datasheet, p. 16). The ESP32 has a second I2C controller (ESP32 datasheet, p. 4), so the second module can go on Wire1 with its own pins.

### Why use a DS3231 when the ESP32 can get the time over Wi-Fi?

NTP needs a network at every boot. The DS3231 keeps time with no network and with the board unpowered, on its backup cell at 3.0 µA maximum (Analog Devices datasheet, p. 3).

## More

- [DS3231 RTC reference](https://www.tinkered.ai/components/ds3231-rtc.md): pinout, specs, rules and common mistakes

## Try it

Tinkered simulates the DS3231 RTC on the ESP32 DevKit V1 in the browser, with this wiring and code, free: https://www.tinkered.ai/components/ds3231-rtc/esp32