This work has gone a step further in the field of direct interface circuits by proposing, analysing and testing a circuit for inductive sensors with a variable self-inductance. The proposed circuit uses a low-cost μC to measure the discharging time of two RL circuits formed by the sensor inductance, a reference inductor and an external resistor. The sensor inductance is then estimated through a single-point calibration that applies such discharging times. Two main error sources have been identified: the quantisation of the discharging-time measurement and the parasitic resistances of both the inductors and the digital ports of the μC. Experimental results with different commercial μCs at different speeds have shown that the effects of quantisation predominate when measuring inductances from 1 mH to 10 mH, whereas those of parasitic resistances are more significant from 10 mH to 100 mH. In both ranges, however, it is feasible to achieve a NLE lower than 0.3% FSS and a resolution of 10 bits, which are remarkable values considering the simplicity of the proposed circuit.