Delay Alarm

[jocanon]

I want to make a simple circuit with an alarm connected to a switch where the alarm will sound when the switch is closed/switched on. However, I only want the alarm to sound if the switch has been closed/switched on for at least 5 to 10 seconds or so. Is there a simple circuit or way to accomplish this?

 

[MikeMl]

This delays the Sonalert by ~5sec. The Sonalert sounds for as long as the alarm switch is closed after the initial delay. The time delay is proportional to R1*C1. The delay circuit resets with even a momentary interruption of the switch closure.

 

[jocanon]

This delays the Sonalert by ~5sec. The Sonalert sounds for as long as the alarm switch is closed after the initial delay. The time delay is proportional to R1*C1. The delay circuit resets with even a momentary interruption of the switch closure.

View attachment 96179

Dued, you're the man! Thanks, that's perfect.

Will these parts work:

Rs:
https://www.mouser.com/Search/Produ...5PQvirtualkey53950000virtualkey539-PK-27H25PQ

S1:
https://www.mouser.com/Search/Produ...D01virtualkey67810000virtualkey785-ZM10D20D01

M1 (I am not sure about this one, I got 2N7000 because I want a through hole mounting style, all the 2N7002 I could find were surface mount style. If 2N7000 does not work as a substitute, what through hole style MOSFET would work?):
https://www.mouser.com/ProductDetail/Fairchild-Semiconductor/2N7000/?qs=sGAEpiMZZMshyDBzk1/Wi9bHELEahoDnY1fyKF6A6Ko=

C1 (will change to 22uF if using 12v and need to delay longer):
https://www.mouser.com/Search/Produ...irtualkey59420000virtualkey594-2222-030-26109

D2:
https://www.mouser.com/Search/ProductDetail.aspx?R=1N4148virtualkey51210000virtualkey512-1N4148

R1:
https://www.mouser.com/Search/Produ...E36virtualkey61300000virtualkey71-CCF60-1K-E3

R2:
https://www.mouser.com/Search/Produ...tualkey59420000virtualkey594-MBB02070C2201FCT

V1:
12v dc power supply

 

[MikeMl]

Looks ok. With a supply voltage of 12V, the delay is only ~2.5s, so you may want to change C1 to 22uF.

It may take a large vane on the micro-switch to trip it....

 

[jocanon]

It may take a large vane on the micro-switch to trip it....

When you say large, are you thinking about 3" or so, or bigger than that? I am putting this in a 4" AC duct so it will be tripped when there is airflow. It looks like it takes 0.2 newtons of force to trip it. I don't think that is a lot. All the other such switches I saw were 0.5 newtons at the least.