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The ChronoPi is an extremely accurate real time clock module designed for use with all current Raspberry Pi models with GPIO pins. It is based on the DS3231 temperature compensated RTC (TCXO). It includes a CR1220 battery which should last at least 3-4 years without power…longer if power is usually available. No external crystal or tuning capacitors are required.
The DS3231 has an internal crystal and a switched bank of tuning capacitors. The temperature of the crystal is continuously monitored, and the capacitors are adjusted to maintain a stable frequency. Other RTC solutions may drift minutes per month, especially in extreme temperature ranges…the ChronoPi will drift less than a minute per year. This makes the ChronoPi very well suited for time critical applications that cannot be regularly synchronized to an external clock.
Applications that may benefit from accurate timekeeping include:
The ChronoPi will plug into the GPIO header of a Raspberry Pi single board computer, and will not otherwise interfere with Raspberry Pi connectors or most optional processor heatsinks.
Time information is sent and retrieved over the Raspberry Pi's I2C interface. This is fully supported by Raspbian Linux, which even recognizes the ChronoPi's internal temperature sensor to allow users access to the current ambient temperature.
|Accuracy:||± 3.5ppm at -40C to +85C (~1 minute per year)|
|Power Supply:||2.3 to 5.5 V DC|
|Current:||200uA (active), 840nA (timekeeping)|
|Dimensions:||23mm x 13.5mm x 12.5mm|
|Pin Spacing:||0.1 inches|
The ChronoPi has a top-mounted battery holder – no soldering required. Simply remove the included CR1220 battery from its packaging, and slide into the battery holder. Please ensure the top (marked +) side of the battery is facing the top of the battery holder (also marked +).
The 3V3 and GND pins are used to power the ChronoPi when it is connected to a Raspberry Pi. While typical usage will be with the Raspberry Pi's 3.3 volt GPIO levels, the ChronoPi will also operate between 2.3 and 5.5 volts.
The battery is a 3V lithium CR1220 coin cell, provided with every ChronoPi purchase. You should install the battery before use, to prevent loss of timekeeping during power off cycles.
The SDA and SCL pins are used to communicate with the ChronoPi, using the I2C standard interface. The I2C bus requires pullup resistors from SDA and SCL to 3V3. Since the Raspberry Pi already has the resistors in place, these are not implemented on the ChronoPi itself.
The DS3231 datasheet provides all other necessary information such as registers, maximum voltages, power consumption, and special features.
With the Raspberry Pi power off, plug the ChronoPi into the far left (pin 1) side of the GPIO header as shown below:
dtoverlay=i2c-rtc,ds3231on a new line
ssh(no file extension)
firstname.lastname@example.org(default password is
sudo hwclock -rwhich should display the date and time (example below):
Fri 12 May 2017 20:28:09 UTC -0.737856 seconds
sudo apt-get update
sudo apt-get upgrade(will take several minutes to complete)
sudo apt-get install lm-sensors
sensorswhich should display the ChronoPi temperature sensor reading (example below):
ds3231-i2c-1-68 Adapter: bcm2835 I2C adapter temp1: +27.5°C
sudo nano /lib/udev/hwclock-set
if [ -e /run/systemd/system ] ; then exit 0 fi
#to become the following:
# if [ -e /run/systemd/system ] ; then # exit 0 # fi
CTRL-Xand then press
Yto save the file
sudo shutdown -r now