A fresh CR1632 3V lithium battery is included with every purchase.
NEW: ChronoDot V2.1 released!
The new ChronoDot has been completely reconfigured for easier battery access and replacement. Despite that, it is still pin compatible with the first ChronoDot. The top side of the ChronoDot now features a battery holder for 16mm 3V lithium coin cells. It should work fine for CR1620 to CR1632. We include a CR1632 with each ChronoDot purchase. This battery actually has more capacity (120mAH) than the old battery (80mAH). The battery negative terminal is gold-plated for lasting corrosion resistance, and all copper and soldermask is cleared around the electrode to ensure a strong positive contact.
The RTC chip has been moved to the bottom of the ChronoDot. It does not interfere with use on a solderless breadboard since the chip height is about the same as the plastic spacers on the headers. The chip has been upgraded to the DS3231SN, which is rated for the industrial -40C to +85C temperature range instead of the old ChronoDot's 0C to 70C temperature range. Please note that use at the higher or lower temperatures can reduce accuracy to +/- 3.5ppm instead of +/- 2.0ppm.
The ChronoDot RTC is an extremely accurate real time clock module, based on the DS3231SN temperature compensated RTC (TCXO). It includes a CR1632 battery which should last at least 8 years if the I2C interface is only used while the device has 5V power available. No external crystal or tuning capacitors are required.
Click here for documentation and example code
The DS3231 has an internal crystal and a switched bank of tuning capacitors. The temperature of the crystal is continously 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 ChronoDot will drift less than a minute per year. This makes the ChronoDot very well suited for time critical applications that cannot be regularly synchronized to an external clock. Here is a great article showing how accurate the ChronoDot's DS3231 can be: http://www.switchdoc.com/2014/09/real-time-clock-comparison-results/
Since the ChronoDot needs to read the temperature, it also contains a fairly accurate temperature sensor, accessible through I2C. Stated accuracy is +/- 3C, though the temperature register returns values with a resolution of 0.25C. Calibration may improve accuracy.
The ChronoDot will plug into a standard solderless breadboard and also has mounting holes for chassis installation.
The I2C interface is very straightforward and virtually identical to the register addresses of the popular DS1337 and DS1307 RTCs, which means that existing code for the Arduino, Basic Stamp, Cubloc, and other controllers should work with no modification.
The ChronoDot V1 and V2.1 design files are currently released under Creative Commons Attribution Share Alike 3.0, until a suitable license under the OSHW Definition is available. You are free to use the Eagle schematic and PCB design included in the files below, in accordance with the included license: