DIY LPG Leakage Detector Circuit Without a Microcontroller

The DIY LPG leakage detector circuit is designed entirely around analog and discrete components, operating without the need for a microcontroller or programmed firmware. Power is supplied to the system via a step-down transformer (X1), which steps down AC mains voltage. The alternating current is rectified by 1N4007 diodes (D1, D2) and filtered using a 1000µF capacitor (C1) to provide a raw DC voltage. A 7805 voltage regulator (IC1) then steps down and stabilizes this voltage to provide a clean 5V rail necessary for powering the sensitive MQ-6 LPG gas sensor (GS1) heater and logic circuitry. The core sensing mechanism relies on the MQ-6 gas sensor, whose internal resistance changes when it comes into contact with liquefied petroleum gas. This resistance change alters its output voltage signal, which is routed into an LM393 dual comparator (IC2). The potentiometer (VR1) acts as a variable voltage divider, allowing the user to manually set a threshold reference voltage on the comparator's second input. When the sensor output surpasses this calibrated reference threshold, the LM393 comparator switches its output state high. This signal triggers a TIP122 Darlington transistor (T2), which acts as a high-current electronic switch. Once turned on, the transistor drives a 12V high-gain siren or buzzer (PZ1), producing an immediate acoustic alert to warn occupants of a potential gas leak. Additional resistors are integrated across the schematic to properly bias the transistor, set gain parameters, and limit current to safe levels throughout the printed circuit board (PCB).