Simple (4001 Based) Alarm Circuit

[pinkfloyd43]

After replacing the french doors, rotted wood, the home alarm no longer works as I'm sure I somehow cut a wire. Too late now as found after completing the job. I told the wife that we needed a "different sound" as the doors go to the pool to cover my a$$!

Found a simple alarm circuit but need to add "something" so it ONLY beeps for about 5seconds when the door opens. I have not been working with electronics in 25 years but have a degree, not helping much after all these years.

Any help with input in regards to best approach to adding the functionality that the buzzer only beeps for about 5seconds is appreciated.

Thanks!
JimD

.pdf file of circuit attached

 

[pinkfloyd43]

4001 Based Alarm

Still trying to find a circuit that will beep about 2-3seconds when the door is opened. Found the one attached only to find during simulation that it works the first time and
then does not work anymore. Believe it has something to do with what the "last"
logic levels are?

Again, it's been years and appreciate any input.

Thanks!

 

[Resqueline]

In the last drawing the buzzer is connected directly to the battery.
The output of IC1a should be connected to the top of BZ1, not back to IC1b. Connect the inputs of IC1b together. C1 may not need to be so large, 1/10th should be plenty.

 

[blocka]

Also in cct2 i dont know if the gate will be able to drive the buzzer. Need buzzer specs obv.

Didnt calculate the frequency, but the buzzer probably will have a sweet spot in the frequency spectrum where it will be much louder than other closeby frequencies.
Add a pot to be able to tune the frequency.

 

[ChosunOne]

Good grieficus! That's a complicated circuit for something to beep a few seconds when the door is opened.

I've got a jar full of surplus Sonalert alarms. I'll be happy to send you one if they don't have any handy at your local Radio Shack. They sound when anything from 1.5VDC up to...well, higher than 12VDC, which is as high a battery as you want to use. You'll probably go with a 9V.

Start with a magnetic reed switch, NC. Now that's NC as electronic folks understand it: If you buy it from an alarm dealer, be advised that alarm industry nomenclature for NO and NC is opposite from the rest of the electronics industry. So the switch I'm talking about is NC = closed when not influenced by a magnet, and open in a sufficient magnetic field. If you buy from an alarm dealer, ask for an "Open loop switch", which they call a Normally Open switch but is actually a normally closed switch, as we understand the term.

Mount the switch on the door however you plan to do it, with its magnet in place to keep it Open while the door is closed. Again, this is opposite of the usual alarm switches, which are closed in a magnetic field. So the ones that go with your home alarm system probably won't work.

You need a resistor and a capacitor, I'm guessing about 1000-2000mF and maybe 10-20K ohm--not sure, but once you see how this works, you can do the math or just trial & error, whichever suits you.

You run the circuit Battery-->NC mag switch-->capacitor-->Sonalert---Back to battery. Parallel the resistor across the capacitor.

When the door is opened, the switch closes and the capacitor passes current to the Sonalert for several seconds until it's charged and blocks any more current. The resistor is large enough that it won't pass enough current to drive the Sonalert, but will drain the capacitor in maybe half a minute after the door is closed.

The fact that the sounder won't work instantly when you close the door is an upside rather than a downside:You don't need the sounder beeping every single time when the door is busy. It tends to drive people nuts. You need it to sound when the door hasn't been opened for awhile. You can adjust the resistor value to your judgment.

Sorry I'm not posting a nice schematic with this, but frankly the circuit is so simple I doubt you need one.