Qwiic RTC - RV-1805

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The Qwiic RTC from SparkFun is a very unique and exciting Real Time Clock. It is extremely precise (within 3 minutes over a year!), extremely low power (less than 22nA!) and has all the necessary oscillators and back-up power making it very compact.

The RV-1805 from Micro Crystal has not one, but two internal oscillators: a 32.768kHz tuning fork crystal and a low power RC based oscillator. The RV-1805 automatically switches between oscillators using the more precise crystal to correct the RC oscillator every few minutes. This allows the RTC to maintain a very accurate date and time with the worst case being +/- about 3 minutes over a year. Very few RTCs can come close to this.

The RV-1805 and the library we’ve written operate the RTC at 22nA. This is extremely low power. No external battery needed! We’ve included a 0.22F super cap on the Qwiic RTC. This should maintain the RTC for over 170 days (nearly 6 months) but we have not had 6 months to test this. For now, we guarantee the super cap will maintain the RTC for over a month. That means you can let board sit with no power or connection to the outside world and the current hour/minute/second/date will be maintained. The RV-1805 RTC has a built in trickle charger: as soon as the RTC is connected to power the super cap will begin to charge and will be fully charged in under 10 minutes. A super cap is superior to coin cells that cannot be charged.

The RV-1805 has an alarm and timer capability. This allows the user to set various alarms and generate interrupts when a certain time is achieved.

Lastly, and perhaps most interestingly the RV-1805 has the ability to switch power to other systems. The RV-1805 has a PSW pin that can sink up to 50mA. This allows it to directly turn on or off a power hungry device such as a microcontroller or RF engine. The RV-1805 can be configured to power up/down the device based on time or external interrupts.

The Qwiic-RTC uses the simple Qwiic interface. No soldering, no voltage translation, no figuring out which pin is SDA or SCL, just plug and go!

  • Precise time keeping with variance of +/-3minutes across 1 year
  • Low 22nA standby current
  • On board 0.22F super cap capable of RTC maintenance for nearly 6 months
  • Square wave output
  • Configurable alarm generation
  • Capable of powering on/off other peripherals with very low power

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