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delayed power-on one-shot

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TonyV

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Hello all.
I just discovered this site and I am really impressed by the great information being exchanged here.

Perhaps someone can help with this:

I would like to build a circuit that, upon power-up, delays a second or two, and then energizes a relay (small reed relay) for approx. 1/2 second, and then de-energizes the relay.

I know I can use a 555 as a one shot, but I'm not sure how to generate the initial delay after power-up.

I used to dabble in electronics all the time as a kid, but it's been many years now. In fact, when I was younger I built a circuit similar to this. When we first got cable TV (1980's!) and our TV did not have a remote control, the cable box came with a remote and would obviously change channels and power the TV on and off. However, the TV always went to channel 2 upon power up. After a couple years, the [3] and [enter] keys on the TV were getting kind of worn out, and it was a huge inconvenience to have to walk up to the TV just to hit the [3] key and the [enter] key. I built a small circuit that fired two relays in sequence and wired them onto the keypad of the TV to hit [3] and [enter] every time the TV was powered up. Of course that TV is long gone and so is my schematic and knowledge of how I did it!


Any ideas?

Thanks!
 
This should do.

Notice that I've left some components blank? The formula to calculate their values is on the datasheet for the 555.
 

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  • Power on pulse.GIF
    Power on pulse.GIF
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