_HowTo: Failsafe(r) use of GPIO pin for critical applications

In an effort to avoid run-away issues with my HVAC system, located on another continend, I wanted to make sure that a crash of the Raspberry Pi that I used as a controller, did not cause a desaster. Also, I needed to prevent Python crashes from keeping the furnace or the air conditioning system running unchecked.

Here is a link to the post that went through the discovery process and with the help of some smart contributors, eventually led to a failsafe design in hardware and software. This resulting hardware and code has been running for about 18 months to my satisfaction.

The post was published on the raspberrypi.org forum : https://www.raspberrypi.org/forums/viewtopic.php?f=37&t=46889&p=432578#p432578

Enjoy!
Paulv

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