Oscilloscope tube/display

Likely you've done this, but maybe look at

I take it you've looked into and rejected using a USB oscilloscope and a computer? The bootup script would be somewhat easier than programming a microcontroller, but it won't start instantly.

Good luck,

bob prohaska

Amazon has color LCD oscilloscopes starting around $30.

I do have a few suitable CTRs hidden away but I wondered if there was a modern alternative. A CRT would need a lot of hardware and extra analogue design; unless I had a source of replacements, I wouldn't want to commit myself to one type which might later be unobtainable

There is no possibilty of including a computer, this is a piece of semi-portable rack-mounting analogue gear with just a few control knobs on the front panel.

I was hoping there might have been improvements in this field, but couldn't find any. Surely there must be a market for a cheap OEM equivalent to a standalone oscilloscope display without all the unnecessary 'features' ?

DIY steampunk audio is a bit of a niche market. ;)

Cheers

Phil Hobbs

This is a professional analogue de-clicker, a portable version of the setup I have been using in the studio to earn my living for the past 30 years. Because it is portable, I was a bit wary about the fragility of a CRT, even though it is to be built into a hefty flight case.

The X-Y scope is used to analyse the movement of the stylus in the record groove, which can reveal all sorts of problems that need correcting to get the best sound quality. A lot of the analogue computing adjustment is done 'on-the-fly', so a separate knob for each function is the only way of controlling it rapidly and accurately enough. Menus and keyboards would be hopeless.

There are lots of LCDs for the Raspberry Pi Pico. The Pico has, I recall, 4 analog inputs.

There is an enormous culture of Raspberry Pi users, clubs, classes. So do what I do, get a kid to program it for me.

Hi Liz, I shopped for digital oscilloscopes a few years ago. (the spreadsheets on EEVblog forum was helpful). I found it gets very pricey or impossible to find high-resolution LCDs. Seems VGA or SVGA is typical. Remedy for this is to pan & zoom the waveform (pinch and zoom on touchscreen), so the LCD's native res is less of an issue. Therefore, I suggest a raspberry pi or similar SBC, where you can plug in your own LCD panel, and choose as high the resolution you desire (or afford). And to easily upgrade it in future as the price falls. So many hits online for "raspberry pi oscilloscope". I like the ones who use external ADC chip, like this:

I didn’t say it was useless, just a bit recherche for the mass market.

Cheers

Phil Hobbs

I appreciate that this is would be a good solution from your position, but I haven't had any contact with that sort of hardware at all. To incorporate it in a piece of equipment would require me to spend many months catching up on developments that I have ignored for the last 25 years.

In less than a week I could make an adequate CRT oscilloscope from scratch and it would do exactly what I want, apart from having difficult-to-replace parts with limited lifespan. (It would also take up a lot more space.)

I wonder if you could take a display with a VGA input and craft something to generate VGA signals.

First you need to generate VGA hsync / vsync. That's some digital counters driven off the appropriate crystal with resets at the right number of counts for the VGA mode and some logic gates to drive the syncs for the right number of cycles. (Look up VGA timings for the details)

Then you could make a comparator based ADC. Feed the X value from your counters into a DAC which feeds a pair of comparators. Put your X signal into the other side of the comparators. Each one is slightly biased so you get a function of (Xinput - bias < counter < Xinput + bias). Do the same with a pair of comparators for the Y side. AND the four outputs together and scale to VGA signal levels.

This makes the logic:

IF (Xpos > Xinput - bias) AND (Xpos < Xinput + bias) AND (Ypos > Yinput - bias) AND (Ypos < Yinput + bias) THEN output := VGA_white ELSE output := VGA_black ENDIF

The 'bias' is the size of your dot. If you want a white dot wire this to R/G/B signals, if green only to G, blue only to B, etc.

By changing the clock frequency and counter wraparound values you can target any standard resolution and timings a monitor can handle, up to roughly

Theo

Other thing though - with this approach you'll get one dot per frame (60 to maybe 144Hz). I suppose what you mean by 100KHz input bandwidth is you want some degree of persistence in the display - even if the dot sweep is

If you had a framebuffer that collected these X/Y locations between frames to build a picture then my setup would work, but otherwise you'd be depending on the persistence of a CRT monitor which is unlikely to be enough.

Theo

Hmm, an electrostatic-deflection CRT and four EF91s would do the job with a lot less bother.

That would definitely be a problem, I am looking at vector movement above audio frequencies, where the angle and amplitude of the movement is important. I have added a differentiator circuit to my analogue X-Y display, which feeds a bright-up signal into the Z input so that these fast movements are emphasised.

A trace consisting of dots would be difficult to interpret and they would have to be updated at 100 Kc/s to capture the effects I am examining.

I think the JYETech Wave2 (with a battery option) would do that, but the display is small.

RL

Yup. Just checked. Set it up and select 'default'. Your settings and display prefs are there at power-on.

RL

Hi Liz, If you need just one CRT unit, try

If you need multiples, try alibaba.com ("Sony Watchman"-like units there). But the minimum order quantity may be a sticking point. Re LCDs, Yes, a little coding, may be invoilved, Mostly cut-&-paste tho. I think if you go to adafruit.com, you'll find many options. You might ask one of the adafruit techs to help point you to the correct setup.

Cheers. Rich.

That would be just right - if only the screen was much bigger. I really need to be able to see detail equivalent to one pixel on that screen - so perhaps it might work with a x2 magnifier that brought it up to the equivalent of 5" diagonal.

I've had a look at the operating manual and the "X-Y" mode shows a sampling rate of 5 kHz in a highlighted panel, as if that is fixed in that mode. I need at least 100 kHz sampling in each channel, otherwise it may miss details.

Just for fun I did a quick web search for electrstatic CRTs intended for lecture-table demonstrations, thinking I'd surely find something. No luck.

Then I looked for Crooke's tubes, thinking they'd be easier to find. No go.

bob prohaska

Although a digital scope may record information that occurred at high frequency, it isn.t going to refresh it's display any faster than the eye can perceive it.

RL