The project came about because of a use case where measurement of a DC sensor needed to be done when only an AC coupled input was available. Time correlation between the AC coupled and DC sensor signals was also required. Very low frequency AC or DC can't be measured with an AC coupled system because there is a minimum frequency created by the impedances of the circuitry. With limited budget and tools available a circuit was the easiest way to capture this data in time correlation with other AC coupled signals. A circuit was designed to complete this task. The obvious choice, the 555 timer. This system is useful to get precision measurements of DC voltages that change relatively slowly. Pressure measurement is an example.

The core functions are shown in the block diagram.

The system was setup to operate from 10kHz to 20kHz. This means the data is capturable with a PC sound card and can be analyzed with free software. With 1 Hz resolution you get 10,000 steps.