Home Articles An RTC expansion module for the Raspberry Pi Pico

An RTC expansion module for the Raspberry Pi Pico

by rp2040guy71

The Pico-RTC-DS3231 is an RTC expansion module specialized for Raspberry Pi Pico. It incorporates high precision RTC chip DS3231 and uses an I2C bus for communication.

More external sensors are allowed to be connected thanks to the stackable design.

 

DS3231 Information

The DS3231 is a low-cost, extremely accurate I2C real-time clock (RTC) with an integrated temperaturecompensated crystal oscillator (TCXO) and crystal.

The device incorporates a battery input, and maintains accurate timekeeping when main power to the device is interrupted. The integration of the crystal resonator enhances the long-term accuracy of the device as well as reduces the piece-part count in a manufacturing line.

The DS3231 is available in commercial and industrial temperature ranges, and is offered in a 16-pin, 300-mil SO package.

The RTC maintains seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator.

Two programmable time-of-day alarms and a programmable square-wave output are provided. 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, to provide a reset output, and to automatically switch to the backup supply when necessary.

Additionally, the RST pin is monitored as a pushbutton input for generating a μP reset.

Features

  • Standard Raspberry Pi Pico header, supports Raspberry Pi Pico series
  • Onboard high precision RTC chip DS3231, with backup battery holder
    • Real-Time Clock Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the Week, and Year with Leap-Year Compensation Valid Up to 2100
    • Optional format: 24-hour OR 12-hour with an AM/PM indicator
    • 2x programable alarm clock

Specification

  • Operating voltage: 3.3V
  • Backup battery voltage: 2.3V~5.5V
  • Operating temperature: -40°C ~ 86°C
  • Power consumption: 100nA(sustains data and clock information)

Purchase

Amazon – Waveshare Precision RTC Module for Raspberry Pi Pico, Onboard High Precision RTC Chip DS3231, Uses I2C Bus for Communication Real-Time Clock Record

AliExpress – Pico Precision RTC Module for Raspberry Pi Pico Onboard DS3231 Chip for RPI Pico

Code example

This is the Micropython example from the link underneath

#!/usr/bin/python
# -*- coding: utf-8 -*-
from machine import Pin, I2C
import time
import binascii
 
I2C_PORT = 0
I2C_SDA = 20
I2C_SCL = 21
 
ALARM_PIN = 3
 
 
class ds3231(object):
#            13:45:00 Mon 24 May 2021
#  the register value is the binary-coded decimal (BCD) format
#               sec min hour week day month year
    NowTime = b'\x00\x45\x13\x02\x24\x05\x21'
    w  = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"];
    address = 0x68
    start_reg = 0x00
    alarm1_reg = 0x07
    control_reg = 0x0e
    status_reg = 0x0f
 
    def __init__(self,i2c_port,i2c_scl,i2c_sda):
        self.bus = I2C(i2c_port,scl=Pin(i2c_scl),sda=Pin(i2c_sda))
 
    def set_time(self,new_time):
        hour = new_time[0] + new_time[1]
        minute = new_time[3] + new_time[4]
        second = new_time[6] + new_time[7]
        week = "0" + str(self.w.index(new_time.split(",",2)[1])+1)
        year = new_time.split(",",2)[2][2] + new_time.split(",",2)[2][3]
        month = new_time.split(",",2)[2][5] + new_time.split(",",2)[2][6]
        day = new_time.split(",",2)[2][8] + new_time.split(",",2)[2][9]
        now_time = binascii.unhexlify((second + " " + minute + " " + hour + " " + week + " " + day + " " + month + " " + year).replace(' ',''))
        #print(binascii.unhexlify((second + " " + minute + " " + hour + " " + week + " " + day + " " + month + " " + year).replace(' ','')))
        #print(self.NowTime)
        self.bus.writeto_mem(int(self.address),int(self.start_reg),now_time)
 
    def read_time(self):
        t = self.bus.readfrom_mem(int(self.address),int(self.start_reg),7)
        a = t[0]&0x7F  #second
        b = t[1]&0x7F  #minute
        c = t[2]&0x3F  #hour
        d = t[3]&0x07  #week
        e = t[4]&0x3F  #day
        f = t[5]&0x1F  #month
        print("20%x/%02x/%02x %02x:%02x:%02x %s" %(t[6],t[5],t[4],t[2],t[1],t[0],self.w[t[3]-1]))
 
    def set_alarm_time(self,alarm_time):
        #    init the alarm pin
        self.alarm_pin = Pin(ALARM_PIN,Pin.IN,Pin.PULL_UP)
        #    set alarm irq
        self.alarm_pin.irq(lambda pin: print("alarm1 time is up"), Pin.IRQ_FALLING)
        #    enable the alarm1 reg
        self.bus.writeto_mem(int(self.address),int(self.control_reg),b'\x05')
        #    convert to the BCD format
        hour = alarm_time[0] + alarm_time[1]
        minute = alarm_time[3] + alarm_time[4]
        second = alarm_time[6] + alarm_time[7]
        date = alarm_time.split(",",2)[2][8] + alarm_time.split(",",2)[2][9]
        now_time = binascii.unhexlify((second + " " + minute + " " + hour +  " " + date).replace(' ',''))
        #    write alarm time to alarm1 reg
        self.bus.writeto_mem(int(self.address),int(self.alarm1_reg),now_time)
 
if __name__ == '__main__':
    rtc = ds3231(I2C_PORT,I2C_SCL,I2C_SDA)
    rtc.set_time('13:45:50,Monday,2021-05-24')
    rtc.read_time()
    rtc.set_alarm_time('13:45:55,Monday,2021-05-24')

When run I saw this in the REPL

2021/05/24 13:45:50 Monday

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