555 Timer based Smoke Detector Circuit Diagram and Its Working

Smoke detectors are one of the most amazing inventions due to mass production and less cost practically. Every year these detectors save thousands of lives due to this, it is recommended for every home. These devices mainly include two basic parts, namely a sensor and a buzzer. A sensor is used to detect the smoke and a buzzer is used to generate the sound to alert the people. These devices can run off of a 120V house current or a 9V battery. For instance, if there is a smoke in your home, then the smoke spreads all over the room and you need these alarms to give you time to escape from the home to save their lives. By using these detectors we can reduce the chances of fire accidents. In this article, we will discuss about what is a smoke detector, smoke detector circuit and its applications.

Smoke Detector
Smoke Detector

What is a Smoke Detector?

A smoke detector is a one kind of an electrical device that detects smoke, generally it is an indicator of fire. Commercial security detectors generates a signal to a fire alarm control panel as a part of a fire alarm system, where as household security detectors generally generates a buzzer sound from the detector itself. These detectors are kept in plastic enclosures and usually designed like a disk about 6 inches diameter and 1 inch in thickness, but size and shape can vary.

Smoke Detector Device
Smoke Detector Device

Smoke can be sensed either photoelectric or by ionization, smoke detectors may use either or both the methods. Smoke detectors are used in an industrial, residential and large commercial buildings are powered with a battery back up. The range of domestic smoke detectors are from individual powered battery units to various interlinked powered units with battery backup.if any component detects the smoke then all activates even there is no electricity.

The estimated detectors installed in the year 2013 are 93% of US homes and 85% of UK homes. The US NFPS (National Fire Protection Association) guesses that nearly two-thirds of demises from home fires happen in goods without working smoke detectors.

555 Timer based Smoke Detector Circuit

Here is a simple smoke detector circuit using a 555 timer. This circuit is used to notice smoke and generate an alarm when the air is polluted. The circuit uses a 555 timer and sensor and the sensor module activates the oscillator and produces an alarm through the loud speaker.

The photo interrupter module comprises of a photo transistor and an LED. The light which is generated from the light emitting diode falls onto the photo transistor, this creates the collector terminal to go potential of ground and triggers the reset control of the IC 555 timer.

Smoke Detector Circuit
Smoke Detector Circuit

If there is an intrude on the track of LED and Photo transistor as smoke, the light emitted from the LED doesn’t reach the transistor, producing the collector voltage around equal to supply voltage. It is directly fed to the RST (reset) pin of IC NE555, which is wired as an astable multivibrator.

The high voltage at the reset pin allows the IC and it generates square waves continuously, which in turn pushes the speaker through a coupling capacitor. Here the astable multivibrator is designed as an AF oscillator with 379Hz frequency and also a loudspeaker is used to hear the alarm.

Maintenance of Smoke Detectors

The various steps in the maintenance of smoke detector

  • Maintenance of smoke detectors can be done by testing once in a month.
  • Rep
  • lace the batteries yearly twice in the detectorsDon’t deactivate smoke detectors even temporarily.
  • Regularly cleaning your smoke detector can keep them functioning properly. ƒ
  • Once every ten years replace the detectors
  • Design regular drills for fire to confirm that everyone identifies closely what to do when the smoke detector generates sound
  • If you are constructing a new home, consider installing a smoke detector to reduce the risk of dying from a home fires and to save hundreds of lives in a year.

Applications of Smoke Detectors

Smoke detectors are suggested for a common use as they give the maximum level of protection. These devices can be used in leakage routes to offer sufficient early warning to let the clearing of residents.

There are two kinds of smoke detectors namely ionization and optical that are familiar as well general purpose detectors and they are accessible in both analogue addressable and conventional.

Ionization smoke detectors are highly sensitive to burn quickly and flaming fires that generate small smoke particles. These detectors are used widely for workshop printings, paint stores, paper mills and also used for general purpose

Optical smoke detectors are apt for detecting slow burning, fires smoldering which generate large smoke particles. These detectors are used in bedrooms, electrical switch rooms and escape corridors and also used for general purpose.

Thus, this is all about smoke detector circuit and its working, applications and maintenance of smoke detectors. We hope that you have got a better understanding of this concept. Furthermore, any queries regarding this concept or electrical and electronics projects, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what are the types of smoke detectors?


  1. can we get equation for this plz

    1. Tarun Agarwal says:

      Hi Sunil
      It doesnt have any equation
      Thank you so much for your feedback
      And once again please visit our domestic website https://www.edgefxkits.com/
      For more details please contact to Sathish on +91 8885507011 or you can email us on info@edgefxkits.in

    2. Tarun Agarwal says:

      Hi Sunil
      It doesn’t have any equation
      Thank you so much for your feedback
      And once again please visit our domestic website https://www.edgefxkits.com/
      For more details please contact to Sathish on +91 8885507011 or you can email us on info@edgefxkits.in

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