Turn an Old Analog TV Into a Simple Oscilloscope

An oscilloscope is a simple, yet very powerful device for analyzing and testing electronic signals. The most basic function of an oscilloscope is to show the waveform of an electronic signal by displaying the amplitude over time. That’s all of the information you need to determine the characteristics of any signal, including the wavelength and frequency—valuable information anytime you’re working with electronics. Unfortunately, new oscilloscopes can be quite expensive, which is why you might want to follow edwardcotad’s tutorial to turn a TV into a simple oscilloscope.

The practicality of this setup is quite limited, as there isn’t any easy way to measure the waveforms without additional hardware. But it is very affordable, and all you need for the project is an old CRT (Cathode-Ray Tube) television set and some basic soldering equipment. The author of the tutorial recommends you use this as a signal visualizer, instead of a true oscilloscope. Considering you can often find old tube TVs for free, this could still be a fun weekend project. The author also recommends using a black and white TV, as color tube TVs may be controlled slightly differently.

Warning: Be careful! A tube TV’s flyback transformer can produce high voltages, even after power has been disconnected from the TV. Be sure to take the proper safety precautions!

This entire project takes advantage of how a CRT TV works. The cathode-ray tube produces a beam of electrons, and two electromagnets—one for the horizontal axis and one for the vertical—are used to direct that beam towards a specific part of the TV’s screen. When the electron beam hits the screen, light is emitted. The general convention is to sweep the beam horizontally, move down one line, and then repeat the process very quickly to produce an image. By tying the horizontal sweep to the amplitude of an electrical signal, a basic waveform is shown on the screen—as long as the frequency and amplitude aren’t too high or too low.

To actually accomplish that, you just need to connect your signal wire to the CRT’s horizontal deflection coil. Edwardcotad has cleverly run that signal wire through the TV’s headphone output, but wired in reverse. That way, you can adjust the volume on the TV to adjust the amplitude of the signal input to a range that is suitable for the deflection coil. All you have to do is connect a simple 3.5mm stereo cable to your signal source, and you can see the waveform!