RTC Pi

£9.75 each (including VAT: £11.70)

The Raspberry Pi is a great low cost computer with thousands of different uses but one thing it does not come with is a real-time clock.  This means that every time you switch off your Raspberry Pi it forgets what the time is and you have to manually set it again next time you switch your Raspberry Pi on.

The RTC Pi is a battery backed real-time clock module for the Raspberry Pi.  It keeps track of the time while the Raspberry Pi is switched off and allows the Raspberry Pi to retrieve the current date and time from the RTC Pi when it is switched back on.

The RTC Pi is powered through the host Raspberry Pi using the GPIO port and extended pins on the GPIO connector allow you to stack the RTC Pi along with other expansion boards. The RTC Pi uses the DS1307 RTC real time clock and a CR2032 battery to maintain the date and time when the main system power is not available.

Unlike most other DS1307 based RTC modules the RTC Pi also includes an I2C logic level converter allowing you to connect other 5V I2C devices to your Raspberry Pi.

The RTC Pi is pin compatible with the the Raspberry Pi model B+.

We also sell a Raspberry Pi A+, B+ and Raspberry Pi 2 version of this board.

Introduction:

The RTC Pi is very useful for standalone projects where your Raspberry Pi will not have a network connection and therefore no way to retrieve the current date and time from the internet.

A mounting hole is provided so you can securely bolt the RTC Pi to your Raspberry Pi with our mounting kit (sold separately).

The RTC Pi can also be used on Arduino boards when connected via the I2C bus.

The i2c address for the DS1307 RTC is 0x68. This board is not compatible with the ADC Pi V1 board but is compatible with the Delta Sigma Pi and ADC Pi V2 when alternative i2c addresses are used.

Warning: Do not connect the RTC Pi to your Raspberry Pi when the power is connected without a CR2032 battery installed. This can cause damage to the DS1307 RTC chip.

The RTC Pi uses a CR2032 button battery (battery not included).

Due to shipping restrictions we are no longer allowed to ship the RTC Pi with a battery.

Schematic

Click to download
Click to download schematic PDF.

Mechanical Drawings

Mechanical Drawing

Click image to enlarge

 

How to set and read the time

 

The RTC Pi requires a Linux kernel with i2c drivers such as the Occidentalis system image from http://learn.adafruit.com/adafruit-raspberry-pi-educational-linux-distro/overview which has i2c enabled.

To access the RTC Pi from your Raspberry Pi:

Boot the Pi from that image and execute these commands as root / su user:

First you need to register the DS1307 RTC chip with the I2C address of 0x68:

For Revision One boards use:

echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device

For Revision Two boards use:

echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device

To set the RTC Pi clock with the current system time:

hwclock --systohc

View the current date and time stored in the RTC Pi:

hwclock -r

Set the Linux system time to the value in the RTC Pi:

hwclock –s

To set the RTC Pi with a custom time:

hwclock --set --date="2012-12-25 06:00:12"  --utc

 

Battery Notes: We have had reports that some brands of button cells do not make a reliable connection when fully inserted into the battery holder on the version 1 RTC Pi boards. Moving the battery out by 3-5mm solves this problem.

The schematic for the RTC Pi version 1 can be found here.

Sample Code

We have python 2 and 3 libraries available for this expansion board.  You can download all of the libraries from github at:

https://github.com/abelectronicsuk/

To download the Python 2 libraries to your Raspberry Pi type in terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_Python_Libraries.git

To download the Python 3 libraries to your Raspberry Pi type in terminal:

git clone https://github.com/abelectronicsuk/ABElectronics_Python3_Libraries.git

Download Python 2 and 3 code samples

Tutorials

RTC Pi and Arduino

RTC Pi and Beaglebone Black

RTC Pi and the Raspberry Pi


Product Code: RTC Pi

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