Alcohol Level Tester

The Alcohol Level Tester circuit operates by combining gas-sensing technology with analog LED driver circuitry to provide a visual indication of alcohol vapor concentration. At the heart of the detection stage is the MQ3 alcohol sensor, a semiconductor gas sensor that changes its internal electrical resistance when exposed to ethanol vapors. As the concentration of alcohol increases in the surrounding air, the sensor's conductivity rises, altering the analog voltage output signal fed into the processing circuit. This output voltage is routed into the LM3914 IC, a monolithic dot/bar display driver specifically designed to sense analog voltage levels and drive ten sequential LEDs. The LM3914 features an internal adjustable voltage reference and a precision ten-step divider network that sequentially illuminates LEDs (LED1 to LED10) as the input voltage scales upward. Resistor R1 and the adjustable preset potentiometer VR1 are utilized to configure the reference voltage and adjust the sensitivity threshold of the LM3914 driver, allowing the circuit to be calibrated for specific detection ranges. Power is supplied uniformly to the entire assembly via a stable 5V power supply, ensuring reliable biasing for both the MQ3 sensor's internal heating element and the driver circuitry. All components are mounted cleanly onto a custom PCB and housed inside a protective casing, resulting in a self-contained, standalone analog instrument that requires no complex microcontroller software or programming.