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I have created a 555 delay circuit where output goes down after a delay of T minutes.

The 555 IC is in astable mode and is triggered automatically upon turning on the supply, Vcc.

After turning on the supply, when the output is still on (within T seconds) I turn off the supply for some time, after the supply resumes the timer output should be high for only remaining time.

In other words the circuit should remember the time it has elapsed before power outage.

Eg: Suppose T = 5 minutes . Ideally when the circuit is run without any interruption; the output goes down after 5 minutes. In case I turn off the supply after 2 minutes, and later turn supply on; the timer should only have a delay of 3 minutes

What is the simplest and cheapest way to achieve this?

JYelton
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mahes
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    Seems like a *delay-once, never again* design. How do you know when its OK to reset the 5 minute timer? – glen_geek Mar 20 '20 at 17:48
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    Does this answer your question? [Is the NE555 the IC I need, and if not, what do I replace it with?](https://electronics.stackexchange.com/questions/486156/is-the-ne555-the-ic-i-need-and-if-not-what-do-i-replace-it-with) – Marcus Müller Mar 20 '20 at 17:48
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    The simplest and cheapest way to achieve this is **not** with a 555 timer. – Elliot Alderson Mar 20 '20 at 17:58
  • @glen_geek when timer actually consumes the 5 minutes or through a reset button – mahes Mar 20 '20 at 19:48
  • It's the wrong solution to the problem. You are wasting your time using a 555 for that task. You would have to hold charge on a capacitor with no leakage and a load of tricky circuitry to isolate it when off. Don't bother. – Transistor Mar 25 '20 at 23:18
  • @Transistor Yes I am planning to achieve this with an ATtiny MCU with battery backup. https://electronics.stackexchange.com/questions/219353/battery-backup-supply-switch-over-design – mahes Mar 26 '20 at 11:49

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