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This paper analyzes theoretically and experimentally the current consumption in direct interface circuits, i.e., circuits in which the sensor is directly connected to a microcontroller ( μC) without using either a signal conditioning circuit or an analog-to-digital converter. The theoretical analysis, which takes into account the current consumed by both the internal electronics of the μC and the external components, proposes formulas to estimate the average current consumption in active mode. The estimated values fairly agree with those obtained in the experimental tests carried out by an AVR ATtiny2313 μC at different operating conditions. For example, the current consumption in active mode at 3 V-4 MHz was about 1.5 mA for the measurement of a 1-kΩ resistive sensor and 0.6 mA for the measurement of a 177-pF capacitive sensor. The results reported herein are expected to be useful for the design of direct interface circuits intended for battery-powered measurement systems.