Ok here we go.

At my work (A petstore) we have a huge aquarium section.

On those aquariums, we have a timer (digital like this, just way bigger)

The timer is set to start waterchange 2 times each day on 3 different groups, and we have a option on the timer so we can make manual waterchange - And here is the problem.
When we start manual waterchange, and forget we put it on, ya well.. the water will run untill we turn it of.. 02.00 this night, I got a call that our power was shut of, and I get to the store found that the water has been running from 17:30 till 02:15 when I got there. (my boss forgot to turn it off) and vupti, all fish in one section was dead..

I've earlier worked with the 555 timer and a relay, and found it very easy.
What I want to do, is when the timer get a signal, it should turn on the relay (pump) and run for eg. 20min and then turn of.
(I can only provide 220v here, so some sort of converting to 9-12v should be made)
The timer should first be "restarted" when the signalpower is turned of.


Hope you understand my problem - and if you have other solutions, please let me know!


Thanks!

 

Here is a circuit:

http://www.eleinmec.com/article.asp?4

If you press the trigger button the timer will turn on the 'device' and after some amount of time it will turn it off. if you press the trigger button again it will turn it on.

 

What if there still is a load on the "trigger" when the time is up? will it continiue then?

I think I just can use a 220v -> 12v relay on the trigger side, and a 12v -> 220v relay on the timer side.