Mirko Pavleski Builds the "Simplest Small CRT Oscilloscope" to Show How Easy It Can Be
Built using a low-cost two-inch CRT tube and a handful of components, this triggerless analog oscilloscope is as simple as it gets.
Maker Mirko Pavleski has built a compact oscilloscope — eschewing modern digital storage oscilloscope (DSO) technologies in favor of going back-to-basics with a tiny cathode-ray tube (CRT).
"Nowadays, analog (CRT) oscilloscopes are no longer produced, but only digital ones, due to their huge advantages," Pavleski explains of the reason you no longer have to dedicate a massive chunk of desk space to your test equipment. "One of the advantages of analog oscilloscopes is real-time, high-resolution imaging of the signal, and [they are] also easier to use than digital oscilloscopes."
With this in mind, Pavleski has shown off what he calls "the simplest possible way" to build your own analog oscilloscope — using a compact cathode-ray tube measuring around two inches at the screen end.
"Let me say that this is not a serious instrument," Pavleski admits of his creation, "but only a demonstration model to describe the way these instruments work. In previous years, this device has been described in several magazines and portals, but I could not find any pictures or a video presentation of its operation anywhere. So I decided to make it and present the results to you."
Pavleski's oscilloscope is built from the bare minimum of components: the CRT, marked only as "5LO381," connected to a power supply with an LM317 voltage regulator and resistor pair for a 6.3V tube heater output plus a boost converter which takes a 12V input and spits out up to 400V for the tube itself. A compact piece of protoboard holds the other components required between the CRT and the input probe: "a few resistors and capacitors," the maker explains.
"The input signal is fed to the Y input via a suitable capacitor to one of the Y deflection plates. For X deflection we use a neon lamp oscillator to generate a timebase, and with a focus regulator circuit we have a complete oscilloscope," Pavleski writes. "Operation of the horizontal deflection oscillator is visible as the gentle flickering of the neon lamp. Whenever the voltage across the parallel-connected capacitor reaches the strike voltage of the lamp, it is discharged with a brief pulse of current. It is hard to imagine a simpler way to generate a sawtooth waveform."
The resulting device, which draws a waveform from a signal applied on the Y input, though with one drawback: support for displaying only a limited frequency. "We get a stable image only at certain frequency values because," Pavleski explains, "for the sake of simplicity, the device does not contain a trigger circuit. My intention is to make a simple horizontal and vertical signal amplifier in the future and adapt this small CRT screen for a simple Arduino oscilloscope clock."
The full project write-up, including schematic, is available on Pavleski's Hackster page.