This paper analyzes the current consumption of direct interface circuits that connect sensors directly to microcontrollers without additional conditioning or conversion circuitry. Theoretical analysis provides formulas to estimate average current draw, which are validated through experiments using an AVR microcontroller. For example, measuring a resistive sensor at 3V and 4MHz drew 1.5mA, while a capacitive sensor drew 0.6mA. The results provide useful guidance for designing direct interface circuits for battery-powered measurement systems.