help with a door alarm!

[whiz115]

Hi!

i found on a store a very tiny and cheap door alarm!

they work with 3 small button cells they have a very small circuit with a piezoelectric speaker an inductor a transistor and an IC covered with a black material i think resin? like on digital clocks... (btw what kind of process is that? how is it made? and why not a normal packaging?)

i have 2 of these alarms...and the specifications are 90db...
i want to transform them to car alarm.

my questions:

1) if i use both of them the total output would be 180db?

2) I want directions so i can build a very simple delay circuit so when i open the door i can have 2-3 seconds to disable my alarm.

3) how can i implement a vibration sensor? and what can i use?

4) the button cells how long they can survive on the alarm if they don't
work without messing the place with liquids?! lol...


thanks!

 

[audioguru]

1) if i use both of them the total output would be 180db?

90dB from one alarm is loud. 120dB would be extremely loud. 150dB is the loudest sound ever produced. 180dB is so loud that it is impossible.

Two 90dB sounds add to make 93dB. A 3db increase is double the power. It is just slightly louder. 10 times the power (10 of the alarms) sounds like only twice as loud.

2) I want directions so i can build a very simple delay circuit so when i open the door i can have 2-3 seconds to disable my alarm.

3) how can i implement a vibration sensor? and what can i use?

People ignore car alarms because they alarm by themselve as a false alarm when nothing happens.

4) the button cells how long they can survive on the alarm if they don't work without messing the place with liquids!

A button battery cell is sio small that it doesn't last long.

 

[whiz115]

you are right Audioguru 3db is double the signal...so 2 alarms double
the output to 3db... i knew it but i couldn't imagine it for the specific
thing. by the way do you really believe each one can output 90db? is it possible
from 3 small button cells?

People ignore car alarms because they alarm by themselve as a false alarm when nothing happens..

yeah i know...but it might scare someone who doesn't expect the existance of an alarm. It's better from nothing.

A button battery cell is sio small that it doesn't last long.

of course...but i don't mean how much time they can last powering the alarm continuesly... these small alarms if they don't activated they don't consume energy so i mean how much time they can last before the buttons start to degrade and release liquids that might damage the alarm.

 

[audioguru]

The sound level might be 90dB when you hold it at your ear like an earphone. Speaker sound levels are spec'd at 1 meter distance.
Sound level decreases 6dB per doubling of distance because the sound spreads out.

 

[whiz115]

The sound level might be 90dB when you hold it at your ear like an earphone. Speaker sound levels are spec'd at 1 meter distance.
Sound level decreases 6dB per doubling of distance because the sound spreads out.

interesting! i also knew it that but i couldn't understood it too...

so because we don't deal with a speaker... probably the 90db measurement is not 1 meter far but close to the source

so can you help me with my build?

 

[audioguru]

What does the alarm detect? When sombody touches the metal door handle it is on? A car is much bigger than a door handle so maybe it will alarm all the time or never.

 

[whiz115]

What does the alarm detect? When sombody touches the metal door handle it is on? A car is much bigger than a door handle so maybe it will alarm all the time or never.

well...it works with a magnet and an magnetic contact (basicaly the contact is two wires very close togather.. )

what i want to do is to make a vibration contact to activate the alarm when someone and also i want to use some contacts on the doors so if someone opens a door the alarm gets activated....but probably if the door is closed the alarm will stop hahhaha

 

[audioguru]

A vibration sensor will activate the alarm whenever a motorcycle or truck drives by and when a jet plane flies by. Many false alarms.

If you lock the car then nobody can open a door except you.

 

[whiz115]

A vibration sensor will activate the alarm whenever a motorcycle or truck drives by and when a jet plane flies by. Many false alarms.

haha! noise pollution preventer? i don't disagree... car alarms can be
very annoying late at night...

ok then i want to make it work as follows (the other thoughts
are a bit difficult anyway..) i'll use a metal contact under the plastic
car door handle which it will be connected with the alarm and when
someone has violated the lock and tries to open the door from the handle the alarm will sound...how can i do that? and also how can i keep the
alarm sound for at least 30 seconds?

i thinked of the use of a transistor were the base could be connected with
the metal contact under the handle, but my simple idea i think it will have poor results... also i need something to keep the alarm for about 30 seconds....

If you lock the car then nobody can open a door except you.

for sure!
Audioguru they don't even need to brake the lock or the glass so they can enter inside! i have faced both braking my lock with a screwdriver and also
without creating any damage to the car...

the alarm porpuse will be to scare (if possible...) and not to become annoying for my neibours

your knowledge is valuable! thanks

 

[audioguru]

A 555 is a timer IC. You can set it to have an output to run the alarm for 30 seconds when it is triggered.

You said the alarm is tiny, cheap and runs from 3 button battery cells. Can anybody hear it?

 

[whiz115]

A 555 is a timer IC. You can set it to have an output to run the alarm for 30 seconds when it is triggered.

You said the alarm is tiny, cheap and runs from 3 button battery cells. Can anybody hear it?

very small and very powerful.... check the photos to get an idea of the
size and the circuit.

yeah i can guess that i probably need a 555, but as you know i'm new on electronics and i can't manage it totaly alone.... i just had an idea to turn this door alarm to car alarm, and i made the above quick thoughts.

btw i find it great idea if i could also use a vibration sensor... i found
a small circuit based on piezoelectric buzzer as sensor... you probably have oposite opinion but it would be great if i can impliment because it's useful function and i can also learn something on how vibration sensors work.

 

[audioguru]

A Piezo beeper is at its loudest when the voltage fed to it is high. 3 Button battery cells produce a low voltage.
Many piezo beepers have a max allowed voltage of 24V. Then they are loud enough to be an alarm. Smoke detectors use a 9V battery.

Car alarms don't use a little beeper. They use a powerful horn loudspeaker with a powerful amplifier driving it.

 

[Hero999]

The piezo circuit in the photograph has little transformer (the black cylinder at the top of the image) to increase the voltage and make it much louder.

 

[crusty]

Go to the store around christmas, they have jingle bells that attach to your door knob, bam instant door alarm without batteries. I've got one of all of my doors and can hear even if someone knocks on it, the bells jingle, awesome.