DS3231-based RTC HAT for Raspberry Pi with coin cell battery backup and I2C interface. The DS3231 has a temperature-compensated crystal oscillator (TCXO) rated ±2ppm from 0–40°C, making it significantly more accurate than PCF8523-based alternatives.
Pi 3.3V rail for DS3231 supply
Pi 5V pass-through rail
I2C data
Pi 5V pass-through rail
I2C clock
Ground
DS3231 square-wave/interrupt output pad
DS3231 32 kHz output pad
Backup battery positive for DS3231 VBAT
Backup battery negative / ground
| Pin | Position | Type | Function | Voltage |
|---|---|---|---|---|
| 3V3 | Raspberry Pi 2x3 header pin 1 | Power | Pi 3.3V rail for DS3231 supply | 3.3V |
| 5V | Raspberry Pi 2x3 header pin 2 | Power | Pi 5V pass-through rail | 5V |
| SDA | Raspberry Pi 2x3 header pin 3 | I2C | I2C data | 3.3V logic |
| 5V | Raspberry Pi 2x3 header pin 4 | Power | Pi 5V pass-through rail | 5V |
| SCL | Raspberry Pi 2x3 header pin 5 | I2C | I2C clock | 3.3V logic |
| GND | Raspberry Pi 2x3 header pin 6 | Ground | Ground | 0V |
| SQW | JP1 pad 1 | Signal | DS3231 square-wave/interrupt output pad | 3.3V logic |
| 32K | JP1 pad 2 | Signal | DS3231 32 kHz output pad | 3.3V logic |
| VBAT | CR1220 holder positive terminal | Power | Backup battery positive for DS3231 VBAT | 3V coin cell |
| GND | CR1220 holder negative terminal | Ground | Backup battery negative / ground | 0V |
Pi 3.3V rail for DS3231 supply
Pi 5V pass-through rail
I2C data
Pi 5V pass-through rail
I2C clock
Ground
DS3231 square-wave/interrupt output pad
DS3231 32 kHz output pad
Backup battery positive for DS3231 VBAT
Backup battery negative / ground
DS3231/DS3232 temperature-compensated RTCs, the budget PCF8523 and DS1307, the Si5351A clock generator (8kHz–160MHz), and bare 16MHz crystals — matched to drift tolerance and supply voltage.
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