Energy Leak Detection Circuit: Build Your 20°C Thermistor Detector

Description

This delicate circuit is fundamentally a comparator, detecting very minor temperature shifts relative to the surrounding temperature. It was initially designed to identify drafts around doors and windows that cause energy loss, yet it can also be utilized in various applications requiring a precise temperature change sensor. Two LEDs are employed to signal whether the temperature alteration indicates a rise (Red LED) or a drop (Green LED) compared to the ambient temperature.

Circuit operation:

IC1 functions as a bridge detector and amplifier: its output voltage increases when temperature rises and vice-versa. This occurs because the n.t.c. resistor R2 reduces its resistance value as temperature increases and decreases, thereby unbalancing the bridge constructed by R1, R2, R4, R5. IC2A and IC2B comprise a window comparator, and R8 serves as the sensitivity control. Prior to commencing a measurement, the circuit must be calibrated using R1 to ensure that both LEDs remain off. If R8 is set to zero resistance, the circuit sensitivity will be at its maximum, and one of the LEDs will illuminate when a minimal temperature difference is detected. As the value of R8 increases, the circuit sensitivity will diminish.

Circuit diagram:

Parts:

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