A Cmos 4060
Burglar Alarm
Description:
This is a single zone alarm - with automatic exit, entry and siren cut-off
timers. It will accommodate all the usual types of normally-closed input
devices - such as magnetic-reed contacts - foil tape - PIRs
etc.
When the alarm is activated - the siren will sound for
a fixed length of time. Then it will switch off - and remain off. The alarm
will not re-activate.
I've used a 12-volt supply in the drawing - but the circuit will work at
anything from 5 to 15-volts. All you need do is select a siren, buzzer, and
relay to suit the voltage you're using.
Schematic
Diagram:
Notes:
When you switch the alarm on - the buzzer will sound eight times. This is the
exit delay. Before the end of the eighth beep - you can leave the building
without activating the alarm.
R6 controls the length and speed of the beeps. It can be adjusted to give an
exit delay of anything from about ten seconds - up to about a minute. After the
eighth beep - the buzzer should stop sounding. This confirms that the loop has
been restored within the time allowed.
If the buzzer does not stop - but changes instead to a continuous beep - the
loop is open and the building isn't secure. When this happens - you should
switch off the alarm - and check for open doors, windows etc.
When you return and open the door - the buzzer will
sound again - and the entry delay will start. The entry delay is the same
length as the exit delay. But to distinguish it from the exit delay - the
buzzer will sound continuously.
If the buzzer is sounding continuously - the alarm has been activated - and the
entry delay has begun. If you don't switch the alarm off before the entry delay
expires - the siren will sound.
The siren will sound only once. Just as R6 sets the lengths of the exit and
entry delays - it also sets the siren cut-off time. The siren cut-off delay is
30 times the length of the exit delay. With the exit delay set at 30-seconds -
the siren will sound for about 15-minutes. Then it will switch off - and remain
off.
Of course - you can stop the noise at any time by switching off the alarm.
After the cut-off timer has switched the siren off - the buzzer will continue
to sound. So when you return - if the buzzer is sounding - you'll know that the
alarm has been activated.
Note that D10 is optional. Its job is to sound the buzzer constantly during the
entry delay. It's also responsible for keeping the buzzer going after the siren
has stopped.
If you leave out D10 - the buzzer will beep eight times during both the exit
and entry delays. And - when the siren cuts-off - the buzzer will cut off also.
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