off switch that automatically turns on/off after few seconds

[tthoang86]

auto on off switch

hi.
I need some help.
I want to make a on off switch that auto turn on off after few sec
(well. more ideal one is just keep flick on then off continuously when connect to power)

thanks for any help

 

[VVV]

Re: auto on off switch

I think you can use a 555 with a relay.

 

[daviddlc]

Re: auto on off switch

Based on your comments seems like you have a battery operated device and then when it is connected to the AC power to switch to use that source.

Am I correct ?

 

[desperado1]

auto on off switch

Suppose I want a 12 hour timer...........that is i want to use a switch that is on during the night and off during the day. Is it possible to construct with a 555 timer ?

 

[kspalla]

auto on off switch

large delays requires the RC to have large time constant this is not practical due to leakage current.
You can have a moderate clock, then use a counter and use to trigger these delays.

 

[desperado1]

Re: auto on off switch

large delays requires the RC to have large time constant this is not practical due to leakage current.
You can have a moderate clock, then use a counter and use to trigger these delays.

i.e. What's the maximum possible time delay that i can get with 555 timers ??

 

[nandhu015]

Re: auto on off switch

i.e. What's the maximum possible time delay that i can get with 555 timers ??

That depends the quality of the components used. You have to check it on your own.

Best practice is generate high frequency and use a divider (counter)

Regards
Nandhu

 

[VVV]

Re: auto on off switch

A couple of hours is about the maximum you can get reliably.