Design and Evaluation of an LM35–LM3914 LED Thermometer for Real-Time Monitoring

Temperature monitoring is essential across diverse fields such as household appliances, laboratories, industrial automation, and environmental systems. This study presents the design and evaluation of an LED thermometer using the LM35 temperature sensor and LM3914 LED driver for real-time monitoring. The LM35, with a linear output of 10 mV/°C, provides accurate analog voltage corresponding to temperature, while the LM3914 converts this signal into a 10-segment LED bar graph for immediate visual feedback. The circuit was designed and simulated using EasyEDA and LTspice, fabricated on a PCB, and calibrated with a reference thermometer. Testing over a range of 0–100 °C demonstrated excellent accuracy, with negligible deviations from reference readings. The system’s advantages include low cost, simplicity, and suitability for educational, hobbyist, and small-scale monitoring applications. However, limitations such as coarse resolution and lack of digital output restrict advanced integration. Future enhancements may include microcontroller interfacing and IoT connectivity. Overall, the LM35–LM3914 thermometer provides a reliable, low-cost solution with strong educational and practical value.