Many modern electronic circuits contain RC circuits as one of the building blocks. The RC time constant of the circuit mainly decides the rate of development of charge in the capacitor and hence the variation of voltage across it. The smaller RC time constant does not allow to see the rapid voltage change during charging and discharging because the processes is too fast to observe.

        For a typical combination of R=1000 ohm and C=1 µF, the time constant is 1 millisecond which is very short to sense by ordinary meters. Using Phoenix-M interface we can study  the slow charging and discharging of a capacitor.  The inbuilt program by Phoenix  Lab of IUAC is little bit modified to see the charging and discharging of a 470µF capacitor connected with 4.7 kilo-Ohm resistor in series. The calculated RC time constant 'tou' agrees well with the actual experiment.

        The slow development of the voltage across the capacitor  can be observed and the concept of time constant can be demonstrated. Also using software trick we can plot the changing current through the resistance during charging and discharging.

       Using three different combinations of RC components we can study the comparative charging and discharging. The circuit connection digram is same as in the Phm-book but instead of only output pin D3 the pins D3,D2 and D1 are used to connect the three different RC combinations. The voltage changes across the capacitors are recorded through the ADC channels Ch0, Ch1 and Ch2. Instead of block read functions the independent "fd.zero_to_5000()" routine is used. Though it slower the process of recording the voltages, for the demonstration purpose it works well.

    The Tkinter support is also employed to develop the GUI based code. The experience is really facinating and appriciated by students and colleguages.