so in short. I am building a redundant system of multiple atmega micro controllers. The way it works is that they are all connected to a single bar, when the system is booted, the first micro controller will execute it's code and make the bar electrically charged. Once it has been, the system will shut down the universal power supply (The only that is powering all micro controllers at once) and only leave on the one that powers the micro controller that produced the signal.
If the first chip fails to produce the signal, because the second will try to produce a signal AFTER the first one, the second chip's power supply will be activated. Etc etc

The only problem I foresee is if micro controllers can fail and have all their digital pins turned on (Meaning that it would not be able to perform complex functions but would still leaving it's digital pins on)

So my question is, is this possible? Can a micro controller fail but still meet my power criteria. Thanks a lot!

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    \$\begingroup\$ Please draw a schematic. \$\endgroup\$ – filo Oct 12 '18 at 15:51
  • \$\begingroup\$ You appear to have no fault detection logic in your description. How does the only MCU left powered on assure it's own state? How does it internally detect failure? \$\endgroup\$ – Jack Creasey Oct 12 '18 at 16:42
  • \$\begingroup\$ Failure is not detected, rather the first working chip is selected by itself, and by virtue of it's activation, the rest are disabled. \$\endgroup\$ – adjustt Oct 12 '18 at 17:12
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    \$\begingroup\$ Then this is NOT a redundant system. Redundancy implies that you can tolerate failures. You have suggested the first to work turns the other MCUs off, they therefore cannot provide redundancy. \$\endgroup\$ – Jack Creasey Oct 12 '18 at 19:06

If you want to be certain that a system enters a valid state (your shutdown, if I read correctly) you need actual command-words sent between the components of the redundant system, or use signals where you can see if it is a fault or a signal. This is because stuck pins can occur in any electronics system, so a line going high or low is not really any form of safe.

The way some equipment solves this is to use the 4-20mA protocol. This ensures that if a pin is stuck, the current in the loop will be out of this range, and it is then easy to detect a fault condition.

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