Home - Blog

Smoke Detecting Circuit -Tested Simple Fundamentals

This project, Smoke Detecting Circuit, is being built without the use of a microcontroller. The smoke detectors are of great use when in need to detect any smoke. The smoke may either be in case of fire or the smoke coming from cigarettes inside a building which may cause a fire. Smoke detectors are the basic precautionary measures in every building, either under construction or fully constructed. This is because the smoke detectors can detect or sense smoke, and then an alarm is generated to let the authorities know about possible fire situations. The fire is then handled within no time, saving precious lives and stuff inside buildings.

This is why this project is straightforward, and one can accomplish it without having high-tech instruments of laboratories. The circuit triggers the buzzer when it detects the smoke or any fire nearby, and an alarm is generated. The circuit comprises the smoke detecting gadget, which is MQ6 smoke, also known as the Gas Sensor for detecting the level of smoke or fire. The sensing gadget MQ6 gas can also detect other elements such as Alcohol, Methane, LPG, etc. A simple transistor is being used to trigger the buzzer, which is the BC547 NPN transistor.

Smoke Detecting Circuit1
Smoke Detecting Circuit1

Smoke Detecting Circuit–Safety precautions

The smoke sensing circuit is susceptible to all kinds of smoke. Therefore you need to be very careful if you have the sensor circuit in your house or room and a regular smoker. This is because the sensor circuit will trigger the alarm or buzzer each time it senses the smoke of the cigarettes.

Smoke Detecting Circuit2
Smoke Detecting Circuit2


  1. The circuit is working at very low voltages.
  2. There is no need to have additional capacitors in the circuit.
  3. There is a need for a variable DC supply in the circuit.

Smoke Detecting Circuit–Components Required

The following are the basic components required in order to make the smoke detecting circuit.

  1. Bread Board
  2. BC547
  3. 10k POT
  4. Smoke Sensor (MQ6)
  5. Resistors of 1K
  6. Variable Power Supply
  7. Connecting wire
  8. Buzzer
  9. LED
  10. Jumper wire 

Smoke Detecting Circuit–Chart Flow Diagram

The following is the chart flow diagram.

Smoke Detecting Circuit3
Smoke Detecting Circuit3

Basic Circuit Diagram

Smoke Detecting Circuit4
Smoke Detecting Circuit4

Working Principle

The circuit has the MQ6 smoke, also known as the Gas sensor gadget, used for smoke or fire detecting in the air. The transistor, i.e., BC547 NPN, is used for the buzzer or alarm trigger. The 10K potentiometer is used for the calibration of the circuit. In contrast, the circuit is designed to have a voltage divider circuit being used with the MQ6 smoke sensor and the potentiometer. The value of the MQ6 is changing whenever it senses smoke as it has a resistance.

The transistor operating properties are being used to work in the circuit of the smoke detection. The NPN BC 547 transistor is being used, which is turned ON only at 0.7V at its base, and the topology being used in the circuit is voltage divider biased.  The potentiometer is being used for calibration purposes. Whenever voltage is applied at the base terminal, which is less or greater than the 0.7V, which would turn ON the transistor, the smoke sensor would sense the smoke and reduce the device’s resistance, i.e., MQ6 smoke detector. Due to this decrease in the resistance, the voltage across the base of the BC547 is increased to 0.7V. This, in turn, makes the transistor ON and LED lights up, and the buzzer is triggered to start beeping. When the smoke has vanished, the detector is made OFF, and the voltage across the base of the transistor is reduced to a value below 0.7V.

Photo of the Smoke Detecting Circuit

Smoke Detecting Circuit5
Smoke Detecting Circuit5
Avatar photo
Emma Lu
Our professional engineering support saves our customers a lot of trouble and loss. >>>>>> After you place the order, our engineer will conduct technical reviews to make sure the parts can be mounted well/correctly on the boards. We will check if the component packages match well with the Gerber footprints, if the part numbers you provided match well with the descriptions, and if the polarity is clearly marked. >>>>> When your design is ready, please send your Gerber and BOM so we can quote and start!