15-20 second entry delay for alarm system

[shockz]

Hi guys, been playing about tyring to make an entry delay for an alarm for some while now but not having much joy.

I have a keypad connected to a monostable, when i trigger the monostable using one of the buttons it goes high for a given time. The concept is to have the monstable turn on an astable 555 which will then trigger a bistable wich will then latch the main circuit. it is working but not how i would like. when i connect the ouptut of monstable to the astable, the timing of the monstable changes. Also the bistable does not allways trigger in this time perioda. Can anyone suggest some ideas, those of you who know about timing circuits.

 

[DerStrom8]

You forgot this, shockz:

 

[shockz]

yeah might help, thanks derstrom.


this is the schematic i have so far.

 

[MikeMl]

I cant figure out what you are trying to do with the third 555, but here is how to use the first to gate the second on/off. Note that the first period is longer than the subsequent ones.