Our shield for RaspberryPI is the most elegant way to add low-power wireless connectivity to the most popular compact computer in the world.
Featuring a panStamp, this shield releases the computer from having to deal with the low-power wireless communications. Instead, the on-board panStamp acts as a modem connected to the RPI UART (serial port).
This shield also includes a real time IC with battery backup so that we no longer depend on remote NTP servers and Internet connections to get the current time, even after an outage.
Raspbian comes with the UART pre-configured to be used as a serial terminal. In order to use the UART with our shield, we need to free the on-board serial port as shown in this tutorial
Enabling the RTC function also implies doing some changes on Linux. There are many tutorials about this in the net but this is our preferred one. Raspbian has the I2C interface blacklisted. Before running through the above guide, be sure you enable I2C. To do this, edit the file '/etc/modprobe.d/raspi-blacklist.conf' and comment out the line 'blacklist i2c-bcm2708'.
After running through the hwclock guide, run 'sudo update-rc.d hwclock.sh enable' to enable the hwclock at boot. Now, run 'sudo service ntp restart' to persuade ntp to update the local time. The last step is to write this time to the hwclock with 'sudo hwclock -w'