Create a pulse after certain delay on event.

[blizok]

Hi,
I'd like to create some simple alarm, that will call me when the door is open. I found magnetic switch (normally closed) at home, old cellular, bunch of resistors/capacitors and some 741 and 555 a relay, optocoupler.

What i'm trying to do is to use speed dial function of my phone, "pushed" by relay or coupler. Now, all i need is to generate a pulse to drive a relay. it should be delayed after event (magnetic switch open) by 1.5 sec, and it have to be 2 second on high.
I have simulated it on 555s, but in practice it don't work, or work bad.

So is the question: what is the best, more elegant, simple way to create such a pulse. Thanks for sharing!

 

[blooz]

Usually this kind of Delay are produced with help of Monostable MUltivibrators .Could you please show the schematic of the circuit you designed ...

 

[blizok]

Hi,
I used 3 555s

1. Monostable, delay producer.
2. Simply instead of inverter, because next one wants to be negative triggered.
3. Produces pulse of certain width.

In practice i used magnetic switch and 741 as comparator, because there is no zero condition at switch.

See screenshots attached.

1. Schematics itself with each 555 outputs highlited and labeled.
2. Oscillo output "big" waves are from generator, and a single pulse is desired one



Thanks a lot!