For experiments with R/C light switch I needed an oscilloscope. Commercial oscilloscopes are quite expensive so I tried searching on the Internet for some alternatives. I found a software called Xoscope that use a sound card to show signal on monitor. Restrictions are clearly given by parameters of A/D converter on sound card. It is necessary to create a simple circuit for correcting the input impedance and dividing the input voltage.
It's very simple device with a poor properties, but for monitoring of the servo signals (50 Hz) fully complies. To build this is very easy for any electrician.