How could I build a 10 minute time delay relay?
I am planning a carcomputer install using a program I found on this forum which hibernates the computer X minutes after pins 4 - 8 on the serial port are shorted. I want the program to hibernate my computer after 5 minutes. I think this is a great idea, however, I am still paranoid as to my battery draining incase my computer hangs for some reason. As many of you may know, software is not exactly the most reliable. So I was thinking maybe somehow build a cheap 10 minute time delay relay as a failsafe mechanism. When ACC power is lost from the engine shutting off, this would trigger a relay to short pins 4 - 8 causing the program to do a hibernate in 5 minutes. However, when ACC power is lost, this could also cause the 10 minute time delay relay to countdown. Incase the computer does not hibernate in 5 minutes, then at 10 minutes, the time delay relay could activate a main relay switch which would cut off power completely to my inverter, thereby doing a cold shutdown on the computer and not draining my battery. Ive done some searching but have not found anything useful. I was wondering if someone could suggest a way to accomplish this? Thanks.