My project is to sound a short (perhaps 2 second) audible alert when a door is opened up.
And then to reset itself when the door closes.
Again the only time the alert should sound is on the door opening (only 2 second regardless how long the door remains open).
How should I build this?
Should it be 555 or 556 timer based, or 74121 or something else.
And should I use a pezio buzzer for the audible alert.
Thank you
steven

 

What's with the other thread?

modify 555 one shot monostable multivibrator circuit

Did you put the missing wire I indicated?

 

sorry,I did not see the was a page two to the thread postings.
thanks

 

As I said in the other thread, the door switch must be closed when the door is open and stay open when the door is closed.

It is also possible to do it with a momentarily activated switch (or two) when the door opens, but the circuit is going to be bigger.

The timer is set for 5 seconds, for two seconds you need to adjust the timing capacitor/resistor.