WHAT I HAVE: I have a simple circuit that connects to RPI. It's a CMOS555 timer that receives a pulse signal from RPI to keep the timer from reaching the end of the duty-cycle. Should the RPI signal vanish, the pulses will not arrive and the timer duty-cycle will reach the end. At the end of the cycle, the 555 timer will power off a mosfet, and within 3 or 4 seconds, power back on. The RPI is on that mosfet, so this means that if the RPI freezes, after 5 minutes or so, the power will automatically reset.
WHAT I NEED: I need to know when it happens! My idea is to use another 555 timer that will somehow trigger when the mosfet resets (powers off). I can use a GPIO as input connected to the output of the new 555 timer. Once the RPI power resets and the software is back up, I will know of the state change on that GPIO, and that's exactly what I need! I can then send a ground signal (via another GPIO as an output) to reset the 555 back to its original state.
The components for my idea mentioned above could be wrong since I'm not an expert on the subject. Whatever the solution, I just don't want any PIC solutions where I have to do programming to any chips. I'm simply looking for a hardware solution. I only need a schematic, I will design the PCB myself and put it to the test.
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