DC Power Failure Alarm

[Pariston]

Hi,
I've been looking for some DC power failure alarm system for my circuit. Input power is 36 volt and I'd like my mcu to react to sudden drop in voltage. What are the most reliable/long lasting ways of power loss recognition in a dc circuit?

[mhuber1]

I'd use a schmitt-Trigger with a voltage divider hooked up to an interrupt pin of the mcu

[mvs]

GPIO inputs of most MCUs do have some hystheresis and more or less constant threshold levels, so you can connect voltage divider directly to the interrupt pin.
You may need a debounce procedure in software for proper operation (i.e. to avoid interrupt storm).

If you wish to have exact threshold, you can use voltage comparator.  Some MCUs do have built in comparators.

Third option is ADC. It is usually slower and less reliable, but you will get a voltage value to play with.

[thinkfat]

I would advise also to immediately shut off peripheral ICs to preserve some juice for the MCU.