Electronic Circuit : 5 Zone Alarm System

This is a complete alarm system with 5 independent zones suitable for a small office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a "system armed" indicator. The schematic is as follows:

Parts list :


There are 6 100k resistors, R1, R3, R5, R7, R9, R14.
6 1k resistors, R2, R4, R6, R8, R10, R12.
1 220k resistor R11
1 10k resistor R13. All resistors will be 1/4 watt at 5 or 10& tolerance.
5 100n capacitors, C1 to C5. These may be polyester or disc ceramic, 50V working or higher.
C6 1 100uF capacitor. This should be electrolytic have a working voltage of at least 25Volts or higher.
C7 1 1uF capacitor. Electrolytic as for C6.
3 1N4148 Diodes, D1, D2, D3 which should be readily obtainable.
1 1N4001 diode D4.
5 LED's LED1 - LED5. Colour is not important but you may like to use the same colour for zones 2 to 5 and a different colour for zone 1, the entry, exit delay.
1 2N3904 transistor, Q1.
1 4050B CMOS IC for IC1. Note that CMOS 4050BE may also be used.
1 4072B CMOS, IC2
1 4082B CMOS IC, IC3. Note that unused inputs on IC's 2 and 3 should be connected to earth and that the power pins must be connected. IC pinouts can be found here.
1 Relay with 2 changeover contacts. The coil needs to match the circuit, i.e. 12V coil, the relay contacts must be suitable for the load. As the load is a piezo buzzer, there will be little load current, so a miniature or sub-miniature relay may be used.
1 keyswitch
1 NO PBS (for the panic switch).
1 reed relay ( for the re-entry switch).
5 NC contact switches. These can be bought from alarm shops and fitted to doors or windows etc.

That completes the full list of components for this circuit. It is an easy matter, and can be applied to any circuit. With experience you just look at the circuit and order all the components required.
Circuit Notes
Each zone uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Suitable switches can be bought from alarm shops and concealed in door frames, or window ledges.

Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppressor. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key.

Operation
At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.