Real-time Clock (RTC) module on a Raspi2

Document ID: bdb6dc5437e596107e4497ce608d68e0

Introduction:

There is no hardware-based real-time clock in raspis. For sensitive data (such as DB’s and WX data), an RTC in kind of important. This also mitigates time-keeping issues when there’s a loss of power, network connectivity, etc. Here’s the the steps I took in order to get my RTC module working…

Assumptions:

This quick and dirty guide assumes:

You have an understading of UN*IX like OS’s
Your Rasperry Pi is a version 2
You have a DS3231-based RTC module already :-)
Your RPi2 is running Raspbian

Steps:

Plug the RTC module into the GPIO (see https://nicegear.co.nz/obj/images/pi-rtc-module-mounting.png)
The i2c adapter is NOT loaded by default in the 2015-02-02 Rasbian distribution, unlike in earlier versions. To enable it, type sudo raspi-config, then select option 8 (Advanced Options), then select A7 I2C, then select Yes to enable.

run:

echo ds1307 0x68 | sudo tee /sys/class/i2c-adapter/i2c-1/new_device

Add these 2 lines to /etc/rc.local (before the exit 0 statement):
```
echo ds1307 0x68 | sudo tee /sys/class/i2c-adapter/i2c-1/new_device
hwclock -s
```
1. NOTE: I also added hwclock -s to the ntp init script in the start() switch.
Consider removing the raspian fake clock:
```
sudo update-rc.d -f fake-hwclock remove
```
Sync system time with RTC module (hwclock):
```
hwclock --systohc --localtime
```
reboot
See if sysclock and hwclock are sync’d
```
date
hwclock --show
```