Delaying a circuit

[jaj43123]

im working on a project right now where if a door stays open for more than 5-10 seconds, a buzzer goes off warning us to shut the door. ive figured out how to do everything except for the timer. can anyone help?

 

[Agent 009]

you could use a simple relay that turns on a 555 timer...

 

[Exo]

If you get a relay and a transistor to drive it you don't need a 555, Just a RC on the transistors input.

 

[Agent 009]

yup, but u just use the RC circuit to control the time?

 

[Agent 009]

i just wanna know if it's power efficient: the RC circuit should outruns the 555 timer as being less power consuming, but after the opening (and fully charge of the capacitor) the alarm is beeped, and the capacitor should be discharged. How?

 

[audioguru]

The capacitor is discharged by a low value resistor from the door switch.
You don't need a relay unless the buzzer is huge or mains-operated.

 

[jaj43123]

thanks for the help. im a nOOb to this stuff. only in my first year and havent learned all that much. i havent gotten to relays yet and that is what i think i need for this project. i need the buzzer to sound once my circuit is disconnected for more than 5 seconds. any chance someone could explain how ot do this for me? my original plans wont work with what im hooking it up to so that was a bust

 

[David Bridgen]

One of these will work depending upon whether the door switch is normally open (left hand circuit) or normally closed.

**broken link removed**

 

[jaj43123]

thank you. that helps out a lot. figured out some of it by myself but a visual is always better. thanks.