Physical Science International Journal

This project presents the construction of a low-cost, stand alone smoke detector circuit intended for early warning in the event of smoke emissions. The circuit utilizes smoke sensors as the primary detection unit, capable of sensing a wide range of smoke concentrations. A 9V battery supplies power to the system, regulated to 5V using an LM7805 voltage regulator to ensure stable operation of the electronic components. A 10µF capacitor provides additional filtering to smoothen voltage fluctuations. The sensor output is passed through a 10K potentiometer, allowing manual adjustment of the detection threshold and enhancing the system's sensitivity to varying environmental conditions. Once the smoke concentration exceeds the set threshold, a BC547 NPN transistor functions as a switching device, activating an light emitting diode (LED) and a buzzer to provide immediate visual and audible alerts. The TF4 - Open plastic fire (polyurethane) and TF2 - Rapid smoldering pyrolysis fire (wood) was used for the testing.  The device was connected to electricity and observed in an environment without smoke for about six hours. Within this period the alarm component did not sense any smoke around, so it remained off. This indicates the circuit was stable and did not produced a false signal. It was able to overcome dust and noise parameters. The smoke detector's obscuration threshold is 16%/meter. The circuit was built and tested successfully on a prototype board, demonstrating accurate detection and reliable response to the presence of a smoke. The prototype proved energy-efficient, portable, and simple to assemble, making it suitable for use in homes, kitchens, laboratories, and small office spaces.