Six Zone Alarm With LED Display

Six Zone Alarm With LED Display


The circuit was constructed with seven-segment LED to display which zone triggered the alarm while utilizing six independent zones. Buffered CMOS, denoted by suffix B, 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.

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 monitoring7 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 has the following features such as Zone 1 having its own entry and exit times, switch S2 enables a walkthrough test to check all zones and the display, switch S1 is a single pole double throw switch where one position is set while the other is reset, each zone has its own LED indicator, and the 7 segment LED display is used to identify which zone triggered the alarm. With regards to the basic operation of the circuit, when S1 is set as the alarm, S2 can be turned on where the delay is controlled by C8 and R13. The alarm will be triggered with an entry to zones Z2 to Z6 and can be reset using S1. toggle S1 to reset before the expiration of entry timer. A walkthrough can be done if S2 is operating in test mode.

To further explain the detailed operation of the circuit, it is essential to consider that all zones Z1 to Z6 are using typically closed alarm contacts. Zones Z2 to Z6 are direct zones where delay in the alarm is not present when it triggers while Z1 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 C6 will provide radio frequency protection as long wires were utilized.

The use of CMOS IC’s except for IC6 is for high noise immunity and low power static consumption. IC6 acts as the 5V regulator providing power all CMOS Ics while the alarm power supply can be at 12V to 15V. In normal operation, the dual pole dual throw switch S2 is established to a functioning position while S1 is tuned to an off mode of the alarm. The relay RLY1 will not be energized together with the CMOS having no power with this condition because the capacitor C7 will discharge via S1, R17 and D8 while capacitor C8 will discharge via Z1, R1 and D9.

İt is only that all CMOS ICs will be powered by 5V supply when the S1 is turned on. The dual input OR gate CMOS 4001B will have half of the input as the capacitor C11 shortly charges. The output of U7A is high compared to the output of U5A, but will be inverted by U7B then supplied back via R18 to U7A’s input maintaining the circuit intact. The alarm will not sound because Q1 and RLY1 is off due to low output from U7B. When S1 is set, it allows ample time from the exit timer as capacitor C8 slowly charges via R13. The delay is around 52 seconds with these given values. Z1 can be opened and closed during the exit delay zone. After the exit, the 2 input AND gate U5A will go high as the capacitor C8 is charged. At this point, any entry to zones Z2 to Z6 will energize the relay and trigger the alarm. The LED will illuminate the digit corresponding to the zone where the unauthorized entry was made and the circuit will be intact in a high state in which the display continues to show the digit of the triggered zone even if the switch is opened or closed again.

Initially output of U1A is low, and if the entry is done via zone Z1 where the entry timer starts, U1A turns high for a moment and produces high output. the high signal is transferred via D7 to the input of U1A where C7 charges via R15 which is the entry delay that is around 24 seconds based on the given values. In the run position, Switch S2 is normally used but in the test mode, it allows a walkthrough test of the alarm. The input of U7A will not trigger the alarm and is always low in the test mode, while the seven segment display is always illuminated. Entering any zone when all zones are closed will show the number of zone but when two zones are open, the display will not indicate any digit. But the first zone to trigger the alarm will remain shown during the run mode.


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.

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