If you a home hobbiest such as myself, having an oscilloscope is ideal, but may not be economically feasible. However, there is a free option available.
xoscope For Linux is a GTK application which allows you to view signals through your PC's sound card (thus limiting the range to audio frequencies dependent upon the sound card being used). This can come in handy for robotics type hobby projects. Additionally, the author (Tim Witham) has provided a
buffer hardware circuit to buffer the proble similar to a true oscillosope and protect your PC's Line In from excessive voltages.

Installing xoscope
- Download xoscope For Linux.
- Extract the tarball.
- Configure, Make, and Install:
./configure
make
su
make install
- Enable capture from your Line-In audio jack (Gnome):
Open the Gnome Volume Control from the menu: System > Preferences > Volume Control.
Click Capture tab.
Enable capture for the Line-In channel by clicking the "Toggle Audio Capture from Line In" button.
