In this project, we are going to teach you making awesome electronics project ideas. The name of this project is fire sensor circuit.

Fire sensor circuit is very useful to detect any fire or smoke at anywhere. If the circuit  can detects any smoke or fire, then the LED light will glow and the buzzer will make sound to alert the security  team.

The circuit can safe your home, office and other places.

The final circuit design can be seen above. We also thanks to our sponsor JLCPCB( for sponsoring us PCB for this project.


Thanks To JLCPCB. 

  $2 for 1-4 Layer PCBs.

Get SMT Coupons -

Component List - 

1. PCBs

2. Bridge Diode

3. Voltage Regulating IC - 7808

4. Capacitor - 2200µf/25v

5. Resistors – 100 Ω

                       10 KΩ

                       1 KΩ

6. LEDs – 5mm (Red & Blue)

7. Transistor – BD 140

8. Buzzers

9. IR Sensor

7. Power Source – 12v transformer

Fire Sensor Design

The schematic of this fir alarm circuit, along with the PCB layout can be seen above. Here bridge diode and capacitor used to convert AC to DC. To adjust range of this IR sensor, we don’t use any potentiometer.

Transistor Pinout

We everyone know that, each transistor contain 3 legs. And this 3 legs have different names. BD 140 is an PNP transistor. If we count it’s leg from left side, then 1st led “Emitter” 2nd leg Collector and 3rd leg Base.

Connect Power Section

We know that, to convert AC to DC we need bridge diode and capacitor. To make this circuit, 1st we connect bridge diode and capacitor with the circuit. We utilize JLCPCB ( to printout our PCB.

Connect Transistor and Voltage Regular IC

After complete power section connection, now we connect transistor and voltage regulator IC with the circuit. To complete this circuit, we need 7-9v. The voltage regulating IC will helps to supply accurate voltage.

Connect LED and IR sensor

For power supply, we’ll use red LED and for danger alert we’ll use blue LED. When the circuit, get power then the red LED will glow. And for the input signal, we are using IR sensor.

Connect Resistor With The Circuit

To make this circuit, we used 3 resistor. Those are 100 Ω, 10 KΩ and 1 KΩ. We use 1 KΩ resistor for power section of this circuit.

Soldering And Cleaning

Perfect soldering is an important part of this PCBs. While soldering, we have to remember that, there should not any short circuit. After soldering we need to cut-off the extra leg of all electronics component.

Use Heat-Sink and Connect Transformer

Now we connect heat-sink with bridge diode and transformer cable with the circuit. Our circuit is now completely ready for use. Now just plug-in power and enjoy the circuit.