Timer help

[Atti2d]

Hi! I desperately need a design for a timer circuit. What I need is a relay control that will activate the relay for 10 minutes and then wait 4 hours before it does it again... on for 10 minutes, off for four hours, over and over and over... LOL
 
Any ideas or designs that anyone could throw my way would be oh so greatly appreciated! Oh yea, I would prefer to use only components that are common... NTE would be great as there is a local distributer open tomorrow morning where I can pick up supplies.
 
I hope I'm not asking too much... Thanks so MUCH in advance!!!!
Dan

[hotwaterwizard]

Try this link!


http://www.zen22142.zen.co.uk/Circuits/Timing/asym.htm

[mozikluv]

 ;)hi,

since you need a long interval the accuracy of using the 555 is questionable since i believe the 555 was not designed for this although it can still be used. try using a programable timer ic like the CD4536 or the CD4541 w/oscillator. you can program this as long as 36hrs.

[MP]

Actually, the 555 timer time event only functions from the RC circuit triggering it. There is no problem with the 555 timer circuitry for longer time delays. Where most people have a problem with the 555 timer, it is usually traced to the external circutry. You can add a a transistor and usually cure any problem associated with long time delays or weak signals. This will keep the parts count down and keep you from other issues such as noise on the clock/oscillator circuit, etc.

MP