Hi
just wondering if there is any Arduino (or compatible) board with onboard RTC ? I can't find any.
The ESP32 has an onboard RTC.
The STM32F4xx "black pill" boards do. I think the blue pills have it also but I'm not sure.
ok. just it will loose all settings when disconnected.. adding a coin cell seems complicated..
All of the Arduino MKR Boards( Zero,wifi1010, etc.) have an RTC and connectors for a battery along with a onboard charger.
but when you disconnect the Lipo the time is gone..
Yes, but the STM core relies on the HAL for the RTC library functions. The HAL supports RTC in both F4 and F1 series, so yes the Blue Pill. However, the last time I played with this, I found that the F1 implementation didn't correctly preserve the time when the CPU is powered down. The F4 does, I tested that. I have an F4 board with the entire circuit including battery holder so it was easy.
There are many shields with RTC on board, that is the usual "simple" way to add RTC functionality to an Uno.
You need a device that has a separate backup power source for just the RTC element.
I think most, if not all, of the common discrete RTCs require an external power source of one sort or another to keep the timing circuits of the RTC powered when the main power is removed/lost.
If you are looking for an Arduino like board that has an RTC, then one of the Anarduino Mini Wireless boards may be of interest. The wireless module may be optional if you don't need that functionality.
When the ESP32 is powered on it can be set to get the time from the internet.
If the internet is available when that happens. It limits physical portability, there are no universal wifi credentials.
There are many different implementations of RTC.
For example, the RTCs on the STM32s have date and time registers so it does everything for you and you don't need to include logic to account for 28,30,or 31 day months, or leap years. On the other hand, the RTC on the new attinyAVRs is only a 16 bit counter that can count once a second but keeps counting in the deepest of sleep modes. In this instance, if you need to keep track of dates, months, and years, you would have to do the calculation yourself. This simpler implementation would suffice if you only need to keep track of hours, mins, and sec.
Not all of them. Some have binary counters.
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