1. Paul MacDougal Triembed.org Dec 11, 2017
DS3231
Paul MacDougal
Triembed.org
Dec 11, 2017

2. DS3231 “Extremely Accurate I2C-Integrated RTC/TCXO/Crystal”
Real Time Clock
Temperature compensated
Internal crystal
Supports battery backup
SOIC 16 package
Made by Maxim Integrated
$8.35 qty 1 at Digikey

3. Functions Clock – provides you with the time and date.
Square wave output(s)
1 Hz, 1k, 4k, 8k Hz
32k Hz
Alarms to interrupt your Arduino code
Temperature

4. Breakout Boards
Also has 32kB of I2C EEPROM
$5.99 Amazon Prime

5. Breakout Boards $12.28 for qty 5
This is what I purchased. When they arrived, I found out that the interrupt pin was not wired to the breakout pins 
But, one of the breakout pins is NC and with a little rework, I connected the interrupt pin to the NC.
$12.28 for qty 5

6. Register map Address Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0 Seconds
Seconds
Clock 1
Minutes 2
Hours 3
Day 4
Date 5
Month 6
Year 7
Alarm1 8 9 10
Day/Date 11
Alarm2 12 13 14
Control 15
Status 16
Aging 17
Temperature 18

7. Arduino Library There are many available libraries.
I used the one from Adafruit
I did make some changes to allow access to internal I2C read/write routines.
I removed the keyword “static” from the definition of the two I2C access routines.

8. Alarm1 x1111 Alarm once per second x1110 Alarm when seconds match
Alarm when minutes and seconds match
X1000
Alarm when hours, minutes, and seconds match
00000
Alarm when date, hours, minutes, and seconds match
10000
Alarm when day, hours, minutes, and seconds match
For me, the real reason to use one of these is to access the alarm functions.

9. Alarm2 x111 Alarm once per minute x110 Alarm when minutes match x100
Alarm when hours and minutes match
0000
Alarm when date, hours, and minutes match
1000
Alarm when day, hours, and minutes match

10. Examples Example 1 – read the time
Example 2 – enable square wave output
Example 3 – read the temperature
Example 4 – use alarm2 to wake every minute
Example 5 – use alarm1 to wake every 42 seconds
Example 6 – set the time

11. Backup Slides

12. From the datasheet:
● Highly Accurate RTC Completely Manages All Timekeeping Functions • Real-Time Clock Counts Seconds, Minutes, Hours
Date of the Month, Month, Day of the Week, and Year • Leap-Year Compensation Valid Up to • Accuracy ±2ppm from 0°C to +40°C
• Accuracy ±3.5ppm from -40°C to +85°C • Digital Temp Sensor Output: ±3°C Accuracy
• Register for Aging Trim • RST Output/Pushbutton Reset Debounce Input • Two Time-of-Day Alarms • Programmable Square-Wave Output Signal ● Simple Serial Interface Connects to Most Microcontrollers • Fast (400kHz) I2C Interface ● Battery-Backup Input for Continuous Timekeeping • Low Power Operation Extends Battery-Backup Run Time • 3.3V Operation ● Operating Temperature Ranges:
• Commercial (0°C to +70°C) and Industrial (-40°C to +85°C) ● Underwriters Laboratories® (UL) Recognized