Simulation of an alarm circuit

Description| How it works| circuit with timer

This app is a simulation of a digital logic circuit for audio and visual alarming, as shown in the figure below. The circuit allows for silencing and acknowledgement (or acceptance) of the alarm.

Alarm Logic Circuit


.xlsm file(64 KB) (Note - if the file is downloaded as .zip, simply rename it to .xlsm)


This app simulates alarm logic used in alarming systems such as fire alarms, intruder alarms and process alarms in a process plant. The circuit is a combination of logic gates, SR flip flops and an oscillator. The components labelled 'X' are NOT gates and the device marked with an UP arrow is a positive edge trigger. The alarm logic is as follows:

1. The circuit is started when powered up by pressing the 'Turn Power On' button.

2. An alarm event, created by pressing the 'Trigger Alarm' button generates an audio alarm and a flashing visual alarm. Examples of alarm events in real life could be detection of smoke or increasing in the temperature of a reactor.

3. The audio alarm is silenced by either pressing the 'Silence' or 'Acknowledge' buttons or when the alarm condition is cleared by pressing the 'Clear Alarm' button.

4. The visual alarm keeps flashing till acknowledged by pressing the 'Acknowledge' button. If the alarm condition remains, the visual alarm remains on when acknowledged. It clears when the alarm is acknowledged and cleared.

5. The circuit is powered off when the 'Turn Power Off' button is pressed.

The circuit is animated, and the various connections show the energized (logic state 1) and de-energized (logic state 0) states. Electrical convention is followed, green colour indicates the de-energized state and red indicates the energized state. See video below.

Contribution from users - Alarm Ciruit Animation using Shapes

Mr. Peter Bartholomew has modifed the alarm logic simulation to use shapes instead of conditional formatting to run the animation. In his version, the elements of the circuit are built using shapes (lines and boxes) and a macro is used to change the colours as per the logic (see screenshot below). I wish to thank Mr. Peter for sharing his work with me and agreeing to let me share this on this site. His version can be downloaded here (.xlsm file, 39KB).

Alarm logic with shapes

Also See:

Alarm Circuit with Timer

Binary Coded Decimal (BCD) to 7 segment display circuit

Little Man Computer

Simulation of Pendulum Waves

PID Loop Simulator