Delay Door Alarm for 20 minutes

[florinel]

I bought a very cheap, $3 door/window alarm that will be triggered when the magnet is moved away from the reed switch. I want to somehow delay the alarm for about 20 minutes.

I want to install this in a remote controlled model airplane and replace the reed switch with an on/off switch and flip the switch before the plane is taking of. Now the alarm was triggered by flipping the switch, but delayed for 20 minutes. An average flight takes about 10 minutes. After landing, I can flip the switch back, so the alarm will not sound, but in case of the plane getting lost in the forest, in the bushes, or in the corn field, I want the alarm to start by itself 20 minutes after takeoff (20 minutes after flipping the switch)... so we can increase the chances of finding the plane.

Any help is appreciated.

 

[alec_t]

You could use a 555 timer driving a counter to provide the delay (a 555 on its own would be hard pushed to give a 20 min delay).

 

[KeepItSimpleStupid]

Take a look at www.picaxe.com. It should be fairly easy to take a small PICAXE and create a 20 min delay. You just need a few things:

Your power source is probably 6V?

1. A power source between ~2 and 5 V. Switching supplies which use up to 12 V can be found easily searching for "power supply breakout boards".
2. A open drain MOSFET to sound a buzzer.
3. A buzzer.

 

[4pyros]

I bought a very cheap, $3 door/window alarm

Witch one did you get?

 

[Reloadron]

I believe KISS means to click here for picaxe.com.

Using a micro controller for a solution is viable but also involves some added things to do, including programming the uC. Using discreet components has a downside in that it is difficult to use a single timer like the 555 to get long delays. There are other discreet solutions using more components.

Ron

 

[colin55]

Just use a 4060. It takes only a few microamps