So, time is important to microcontrollers. Also, it is important for may circuits that could be built using a microcontroller such as a ATTiny 1626. Also, they are so inexpensive today it is almost not worth bothering to use things such as 555 timers and other components as they can do that work and then some. Overall, they can be a great way to reduce component costs.
The eleccircuit post about a 12 volt to 220 AC 50Hz circuit inspired me to think about this same circuit but to replace the 555 timer with a ATTiny uCPU instead. That way I can tune it via code and add more features to it over time if I so desired to do so. Plus what a great opportunity to make my own UPS. It can have brownout and other options added to it and they are all controlled by the uCPU. After all, the ATTiny 1626 has a great ADC to monitor the AC line voltages and battery state. Also, I can add logic to allow for safe maintenance of the batteries via the attiny. And finally, display all for the info via LCD. Now, I am probably going to upgrade from the ATTiny 1626 to some 32 KB version such as the ATTiny 3226 or even the Mega versions similar to what is in the UNO. Anyway, this circuit is about a timer.
Timer circuit.