Make an Oscilloscope out of your Old B/W TV

Oscilloscopes are very versatile pieces of electronic test equipment that are used in a wide variety of applications. But they are expensive and most of the time students or hobbyists could not afford them. Here is an oscilloscope that you can make yourself with a black and white television. This oscilloscope has 20KHz bandwidth.

This project relies on sampling a waveform and then reconstructing it. The Shannon sampling theorem, which states that samples must be taken at a rate greater than twice the maximum frequency of the original signal (or at the Nyquist rate), is used so that no aliasing occurs. Aliasing occurs when a signal gets undersampled; a waveform of lower frequency will get reconstructed instead of the correct higher frequency signal. A picture is shown below to illustrate the idea:

Source: http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2010/egm23_lad97_rsw35/egm23_lad97_rsw35_website/egm23_rsw35_lad97_final_project_v2_files/image004.jpg

Therefore, in this project, the sampling rate is always set higher than 40 kHz (the oscilloscope functions correctly at a maximum frequency of 20 kHz). The A-to-D converter is responsible for sampling and has a maximum sampling rate of 2 megasamples/sec.

Read details of this project @ Digital Oscilloscope