The modern oscilloscope is truly a marvelous instrument, being a computer with a high-speed analogue front end which can deliver the function of an oscilloscope alongside that of a voltmeter and a frequency counter. They don’t cost much, and having one on your bench gives you an edge unavailable in a previous time. That’s not to dismiss older CRT ‘scopes though, the glow of a phosphor trace has illuminated many a fault finding procedure. These older instruments can even be pretty simple, as [Mircemk] demonstrates with a small home-made example that we have to admit to rather liking.
At its heart is a small 5 cm round CRT tube, with an off-the-shelf buck converter supplying the HT, a neon lamp relaxation oscillator supplying the timebase, and a set of passive components conditioning the signal to the deflection plates. The whole thing runs from 12 V and fits in a neat case. It has one huge flaw in that there is no trigger circuit, and sadly this compromises its usefulness as an instrument. Our understanding of a neon oscillator is a little rusty but we’re guessing the two-terminal neon lamp would have to be replaced by one of the more exotic gas-filled tubes with more electrodes, of which one takes the trigger pulse.
Even without a trigger it’s still a neat device, so take a look at it. Perhaps surprisingly we’ve seen few CRT ‘scopes made from scratch here at Hackaday, but never fear, here’s one used as an audio visualiser.
This is wonderful. 🙂❤️
Tip: I’d add a little bit of shielding inside the chassis, since it’s made of plastic/wood.
Ok, it’s maybe not exactly needed, since the acceleration voltage isn’t that high and because the tube comes with a bit of shielding on its own (unless it’s a bare tube), but.. Well, better safe than sorry. 😅
Scope tubes need mu-metal shielding more to keep the beam deflection accurate, than to protect HV leaks. But since this is by no means a precision instrument, I woudn’t worry much about the shielding. Old TV receivers had a thin wood or plastic case with 20-30 kV CRT anode without major hazards. The CRT is designed to keep anode voltage inside the bottle.
Great project anyway! :)
Except, you know, for the 20-30 keV x-rays. Which need to be shielded by the leaded glass and, when there isn’t enough, the case of the device.
My First Oscilloscope™, brought to you by Fisher Price!
I don’t often say an electronics project is adorable, but this one certainly is!
B^)
So, is this CRT readily available, or long out of manufacture?
I can see something that looks similar using circular LCDs.
My first two oscilloscopes, in the late 1970’s were given to me at the same time, both old at the time. One was a 100kHz one with orange phosphor (I don’t remember the brand), and the other was a 5MHz Eico. I had a friend who made a really nice, very compact tube ‘scope, with a design from a magazine article. He had access to a machine shop, and did a really professional job. Next I got a compact portable Heathkit 20MHz dual-trace triggered ‘scope which turned out to be too much of an assembly project for me, and I quit before finishing it, and let it collect dust for years before getting back to it. It was a nice ‘scope, but I can’t believe I paid about $700 for it, which would be like $2,600 today. The first DSO I used was a nice Philips, at work. Many years later I was given an Agilent DSO1004A which is too smart to be useful. I can’t even get basic readings, because it says, in essence, “No, this is a better setting for what you want,” when it really doesn’t know. It’s user-hostile! I hate it, so I went back to my analog scope. I tried to trade the Agilent one in at one of these test equipment rental places that also sells used equipment, and the amount they offered me for it was an insult. The only problem I have with my analog ‘scopes is that the switches have gotten intermittent but they’re not accessible to spray contact cleaner into the insides of them. I don’t think I’ve ever seen a digital ‘scope that offers XY mode, let alone XYZ (Z being the brightness input with high-frequency capability). An article that came out a year or two ago basically insulted anyone who would even think about getting an analog ‘scope; but what I was seeing was that you could still get a lot more ‘scope for the money in analog.
“No, this is a better setting for what you want,”
I tried using some free video editing software on my PC around 20 years ago and found them (2 different programs) forcing actions that could not be circumvented. (“You are making too many edits!”)
But, since I wasn’t trying to make a professional video, I gave up instead of buying editing software.
All my digital scopes have XY mode, and nicer Tektronix scopes have XYZ (if they’re four-channel models.) I’ve used a Tek 7074 as a display for an old HP source/measure unit that has a failed CRT but has an xyz output.
I agree analog scopes have a lot of advantages, but digital scopes do have a lot of good uses too.
I had a fascination for the two inch face tubes which was handy for tuning the mark and space RTTY signals on the amateur radio bands. A space was a horizontal trace, the mark was the vertical trace. A properly tuned signal displayed a cross pattern. The circuit was a simple op-amp design with each trace predetermined by two individual audio frequencies. The rate and speed of the signal could be tuned in a few seconds.
Interesting!
Back in 1961 I served on the USS Norton Sound, a seaplane tender converted to a guided missile test ship. I worked in the telemetry department where I serviced the Ampex tape recorders. The two were big units, 1/2″ tape and 6 feet high and about 24″ wide. One had levels set by 7 miniature meters and the other had 7 1″ CRTs to do the same thing. I attended Ampex tape recorder school for a week to learn a lot more about tape recording circuits and techniques. I still have one of those CRTs when the ship was decommissioned and I was transferred to a real fighting ship, the USS King, a DLG carrying Terrier 2 stage anti air missiles.
I once saw a piece of equipment at a hamfest or surplus store (Ax-man?) that had a bunch of small B&W CRTs in a neat little array. I don’t recall if they were O-scopes or video monitors, but just the sort of bling that would have given my workbench “street cred”. But, alas and alack, either it wasn’t for sale, or it was priced above my pay grade.
P.s. “Norton Sound” would be a good name for antiviral audio software for a PC.
B^)
Speaking of Norton, there was a real Norton Commander sort of (“Emperor Norton I”)..
The story is quite interesting not to say amusing and can be read here:
http://tinyurl.com/539stk4p
Have fun. ^^
Nicely done! My only comment is their note about the 400v power supply, saying “The power is quite sufficient for any CRT tube..” 400v is /barely/ enough acceleration voltage for all but the smallest of CRTs. I don’t think I’ve come across a scope with less than 1,000V acceleration potential, and even the ‘slow & small’ Tek scopes have around 3,000V, with the bigger ones having post-deflection acceleration voltages on the order of 10kV – 24kV
My First O-scope [TM] was a Bell & Howell/ Heathkit I bought used in the late 1970s. Someone told me a “higher” HV supply was available if one would have liked to see the display and anything else in the room at the same time.
B^)
I don’t know this for sure, but if you split the input signal with one line going to a comparator that served as a simple voltage level trigger, that way you could keep the existing quirky timebase.
Xenon flash tubes are triggered via an electrode on the outside of the glass envelope – I daresay you could manage something similar with a neon lamp.