Help with One-Shot

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In making my preamp with relay input switching, I need to have a circuit that will issue a pulse to the relay network upon turn on because I want automatic selection of input#1 on turn on.

I was thinking about a one-shot, that does this: a 1 second delay upon power up and then a .5 second 5 volt pulse, never to be repeated again except on turn on next time, whenever that happened.

Anyone know of a simple way to accomplish this? I have been looking at one-shot chips and it seems that they require clocks and things like edge triggering that are way too advanced. Perhaps it could be done with a RC network?

I know that this is probably easy, but please help if you can!

thanks as usual.
 
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