The objective of this PFC is to develop a system to determine the impedance of capacitors and batteries from voltage and current measurements in the time domain. The impedance is of interest since this is related to the state of charge and aging of the batteries. It is proposed to transform the voltage and current signals to the frequency domain and thus determine the impedance for different test circuits. We will use different excitation signals with a common characteristic that is using harmonic signals so that we can compute the whole impedance spectrum. We will analyse the transformation to the phasor domain, with special emphasis on errors due to windowing, aliasing, sampling frequency and the ones introduced due to the experimental stage. The experimental results are validated with the corresponding impedance results obtained with a circuit simulation program together with the theoretical simulation of the test circuits to prove the effectiveness and limitations of this method. With this project we can simplify the study of impedances based on impedance analysers to harmonic signal generators systems (square, triangular, trapezoidal ...).