Very nicely done. I second the use of opto-couplers here. There are a ton of reasons for using them. First, they physically separate the two circuits if you power the comparator circuit from an external source. Second, they avoid the "chattering" and other bad properties of relays if you were to go that route. Third, as was noted, transistors often seem to have minds of their own.
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The technology is within the reach of even the smallest nuclear power.
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