I need to build a circuit to open a relay for about 4 seconds at the top of every hour. This needs to trigger an event. I will be feeding dtmf tones to the trigger while the relay is open. Somehow I need this to go at exactly every hour. Someone please help,
If you need an exact delay you can use controllers or something. if the timing is not that much of an issue , can use general purpose timers like 4060 or ne 555(and some circuitry) for the delay. please be elaborate in the problem so everyone can help you out.
I don't think a 555 is stable for an hour. To get that one hour delay, use a PIC.
Lol, before reading BeerBelly's post, i said to myself, get a cheap cellphone, set alarm to go off every hour, and use the output from the speaker as signal to trigger your relay. But, such a task, I only mentioned it coz my thought was similar to his post
That is why we both suggested the 4060. With a crystal, it would be as stable as any watch/clock. We suggested using the 555 only to get the 4 sec period...