I'm looking to implement a watchdog circuit. Tried the standard "missing pulse detector" schematic such as one from http://www.falstad.com/circuit/e-555missing.html - and it works well when the input stuck to high.
However if input stuck to low (for example my application crashes at the exact moment when I'm resetting the watchdog pin), this circuit fails to detect missing pulse. This could be seen in the same schematic with logic replaced by AND.
Is there a reasonably simple schematic which can truly detect a missing pulse, no matter whether input got stuck on high or low? I know there's always MAX6814 or TPL5010 would work, but their price tag isn't attractive (10x-3x of attiny which can do the same).
What I want is basically:
INPUT: 010101010101 OUTPUT: 1111111111 INPUT: 010100000000 OUTPUT: 1111110000 INPUT: 010111111111 OUTPUT: 1111110000