How To Make A Simple Smoke Detector

You went to make a simple smoke detector circuit you need (H21A1) photo interrupter module as a smoke detector sensor, transistor BC547, and 2N2222, resistor, capacitor and you can make this circuit. This smoke detector is highly sensitive but inexpensive. This circuit gives an audio-visual  alarm when thick smoke is present in the environment.


≡ Component and working details:-


  • Resistors: In this circuit, we use 100 ohm, 680 ohm,100k resistors, and 2.2k,1M VR.
  • Capacitor: Capacitor is a two-terminal electrical component and it is used to store electrostatically energy in an electric field. In this circuit, we use a 10uf capacitor.
  • Transistor: In this circuit, we use tow transistor BC548 and 2N2222 transistors. It’s a general-purpose BJT NPN Transistor. BC548 and 2N2222 transistors have 3 pins 1-Collector, 2-Base, 3-Emitter. Current flows in the collector, the biasing of the transistor are controlled by the Base, Current Drains out through the emitter.
  • (H21A1) Photo Interrupter module: In this circuit, we can use the (H21A1) Photo Interrupter module as a smoke detector sensor. H21A1 is an optical consist of the gallium-arsenide infrared emitting diode. This sensor’s sensing distance is 3mm and response time 8-15u.
  • LED: A light-emitting diode(LED) is a semiconductor light.

≡ Circuit And PCB



≡ How to work this circuit :


This circuit used for smoke detectors. In this circuit use a smoke detector sensor (H21A1) photo interrupter module this is the main component in this circuit when the sensor detected smoke in the environment then the sensor throw a signal in the two-transistor T1 (BC547) and T2 (2N2222). The transistor passes the signaled and piezo buzzer and we got the audiovisual alarm and light signal. In this circuit we used two VR, VR1 is used to control the sensitivity of the photo-interrupter module, and VR2 is used to control the sensitivity of  Darlington pair transistors. This is how the circuit works.

Download Circuit Diagram and PCB Click

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