RTCs always need some kind of battery back-up, otherwise, like a night stand alarm clock without a 9V battery, when the power goes out in a thunderstorm, the alarm clock needs to be reset. Fitness bands all have RTCs because most people want to know when and how long an event occurred with respect to times that they can relate to. RTCs are most often used when humans need an MCU to interact with them on their terms. The RTC is a clock, but it’s the kind of clock that people use every day an RTC is a 24-hour clock and/or a Julian calendar. Modern processors are so fast that overclocking isn’t discussed as much anymore because it’s not worth the effort.Īnother type of clock often mentioned in MCU datasheets, however, is the Real Time Clock (RTC). Overclocking can cause problems if overdone. Processors can be sped up by speeding up the clock, within certain limitations. “Overclocking” is sometimes discussed in reference to processors. A 32 mega Hertz (MHz) clock will cause the associated controller to complete 32 million (M) cycles per second (Hz), which is the same as 32 million instructions processed per second, if one full instruction is completed in each cycle. Clock frequency is often discussed with respect to the speed of an MCU or processor. Clocks can be internal or external, and come in many different types and implementations, but they all keep a regular drumbeat for the MCU. Those regular intervals need to have a regular cadence for the MCU to be predictable, so MCUs have at least one clock to keep timing going at a regular pace, much like you would use a metronome to keep pace in piano playing. Microcontrollers act upon instructions a few bits at a time, collecting the next batch of bits at regular intervals. This reduces the amount of required PCB space, and polarized connections mean you can’t hook it up wrong.Figure 1: The DS1307 real time clock breakout board kit by Adafruit is an RTC with coin cell battery and will keep time for at least five years. All Qwiic-enabled boards use a common 1mm pitch, 4-pin JST connector. The SparkFun Qwiic connect system is an ecosystem of I 2C sensors, actuators, shields and cables that make prototyping faster and less prone to error. If you need to use more than one RV-1805 sensor consider using the Qwiic Mux Breakout. A multiplexer/Mux is required to communicate to multiple RV-1805 sensors on a single bus. Note: The I 2C address of the RV-1805 is 0圆9 and is hardware defined. 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. There is also the option to add a battery to the board if the supercapacitor just isn’t going keep your project powered long enough (keep in mind, the supercap can hypothetically make the board keep time for around 35 days), you can solder on an external battery. The RV-1805 also has a built in trickle charger so as soon as the RTC is connected to power the it will be fully charged in under 10 minutes and has the ability to switch power to other systems allowing it to directly turn on or off a power hungry device such as a microcontroller or RF engine. This feature allows the module to maintain a very accurate date and time with the worst case being +/- about three minutes over a year. This RTC module's built in RV-1805 has not one, but two internal oscillators: a 32.768kHz tuning fork crystal and a low power RC based oscillator and can automatically switch between the two using the more precise crystal to correct the RC oscillator every few minutes. However, we still have broken out 0.1"-spaced pins in case you prefer to use a breadboard. This means you get plenty of charge and discharge cycles without any degradation to the “battery." To make it even easier to get your readings, all communication is enacted exclusively via I 2C, utilizing our handy Qwiic system so no soldering is required to connect it to the rest of your system. The RTC is ultra-low power (running at only about 22nA in its lowest power setting) so it can use a supercapacitor for backup power instead of a normal battery. Get with the times, already! This SparkFun Real Time Clock (RTC) Module is a Qwiic-enabled breakout board for the RV-1805 chipset.
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