Five Zone Alarm with LED Display

Overview

The circuit was constructed to be appropriate with small office or home environment which consists of seven-segment LED to display which zone triggered the alarm while utilizing five independent zones

Terminology

• Zone – refers to an alarm control panel’s input from a protective circuit which divides the alarm system into separate independent areas of protection based on function which may include  medical, fire, intrusion, or critical condition monitoring
• 7 Segment LED – is a form of electronic display device for displaying decimal numerals that is an alternative to the more complex dot-matrix displays also known as seven-segment indicator

Circuit Explanation

The design of the circuit was constructed under the operation of 3 buffered CMOS, denoted by suffix B. They were used because the gain is very high; they are sensitive to parameter changes in the oscillator circuit and are less stable than unbuffered ICs. These series of CMOS ICs were generally characterized with small fluctuations of supply voltage, has very high input impedance which means it will not affect the part of the circuit where it was connected, has outputs that can sink and source only about 1 mA to retain the correct output voltage to drive CMOS inputs, can drive up to 50 inputs, fast propagation time with the proper amount of voltage, has frequency up to 1 MHz, and has very low power consumption.

From the operation of the circuit, it is essential to consider that all zones 1 to 5 are using typically closed alarm contacts. Zones 2 to 5 are direct or immediate zones where delay in the alarm is not present when it triggers while zone 1 will function as a timed zone which should be positioned in the main entry and exit point of a building where S1 functions as the set and reset switch, normally a metal type key. Capacitors C1 to C5 will provide radio frequency protection as long wires were utilized. Capacitor C7 and resistor R14 will function as transient voltage suppressor wherein they will react to sudden or momentary overvoltage conditions.

The capacitor C6 is charging via R11 when the switch is ON, which acts as a delay for around 30 seconds. The delay time can be varied by altering the values of either C6 or R11. LED 6 may be arranged externally to provide visual identification that the system has been set. If the system has been armed, LED 6 will light once the timing period has gone by. Even zone 1 will trigger the alarm once any contact gets open after setting the system. The hidden re-entry switch must be activated to avoid triggering the alarm at the entrance of the building. Doing this will begin the entry timer while capacitor C6 discharges. The re-entry switch can be located anywhere in a door frame but not obviously visible and should be concealed. The alarm will trigger when the panic set is pressed. RLA2 controls the siren or buzzer while RLA1 provides the latch as the relay gets energized.

Application

Seven-segment displays are widely used in digital clocks, electronic meters, digital instruments, household appliances, and other electronic devices for displaying numerical information. Generally, LEDs can be used as indicators and signs, in lighting and illumination, in non-visual applications, and light sources for machine vision systems.The circuit will be most used in highly secured premises such as offices, buildings, government and publicly secured places to prevent any unauthorized entry.

Source:www.zen22142.zen.co.uk/Circuits/Alarm/5zalm.html