Quick simple project for CRT ?

Thread Starter

Externet

Joined Nov 29, 2005
1,957
Hi.
Original plan was using one of the CRTs salvaged from a rear projection TV like :

---->

Then found among my other spider webs a vulgar surveillance CRT monitor. Perhaps will be simpler.
Want to feed real-time left audio to vertical and right audio to horizontal to produce lissajeous images, analog monochrome.

1667491334606.png

Have no schematic for the surveillance monitor. I can disable/remove the video cameras input circuitry, disable vertical and horizontal coil driving,... Been reading and looking at a few videos now... If you have ideas on how to feed audio channels to the deflection coils, please advise. Is it just amplifying to a level that deflects to the entire screen or there is more to consider ? Focusing, supplies, controls, biasing, HV untouched ?

1667492021638.png
:D---->
 
Last edited:

MrChips

Joined Oct 2, 2009
27,654
Yes. I did this once a long time ago. I gave away the monitor to a good friend who wanted it more than I did.

I fed one stereo channel to the x-axis and the other the y-axis. I also added intensity control so that the spot dimmed to nothing when there was no content. Thus the lines were brighter at higher volume. If I recall correctly, you want to add filters to provide bass emphasis.

With monophonic signal you just get a diagonal 45° line. With good stereophonic content the display is quite amazing to watch.
 

Thread Starter

Externet

Joined Nov 29, 2005
1,957
OK, thanks. I will then just feed audio level as needed as if the deflection coils were speakers. And attenuate high frequencies, that I did not think about.:)

Same thing here. Someone drooled and mine that ran on electrostatic deflection plates went to a new home.:p
 

MisterBill2

Joined Jan 23, 2018
13,692
I put together an audio scope like that back in 1963. I had an old round screen tv with a 10 BP4 tube, and the set had an oscillator type high voltage supply with a 6V6 oscillator and a 1B3 rectifier, rather then a flyback type high voltage deflection scheme. So I could have X and Y deflections and I used an NE2 relaxation oscillator for a sort of linear horizontal sweep signal. It was cool to watch for a while..
 

DickCappels

Joined Aug 21, 2008
9,505
Most of the CRT displays I have seen used the deflection you in conjunction with a flyback transformer to generate the grid 1, grid 2, focus and anode voltages. If that is the case with your monitor you can use an inductor (probably a large one you make yourself) in the high voltage circuit in place to the deflection yoke, freeing up the horizontal winding for your audio signal.

When this sort of thing is done with magnetically deflected CRTs both windings are often drive by current source - leave that for an improvement later on.

First thing is to light up the tube and get X and Y deflection workign.
 

MisterBill2

Joined Jan 23, 2018
13,692
Most of the CRT displays I have seen used the deflection you in conjunction with a flyback transformer to generate the grid 1, grid 2, focus and anode voltages. If that is the case with your monitor you can use an inductor (probably a large one you make yourself) in the high voltage circuit in place to the deflection yoke, freeing up the horizontal winding for your audio signal.

When this sort of thing is done with magnetically deflected CRTs both windings are often drive by current source - leave that for an improvement later on.

First thing is to light up the tube and get X and Y deflection working.
Substituting an inductor for the horizontal yoke is an interesting concept that I had not considered. Not at all efficient, but quite effective. The oscillator-rectifier HV supply was a very fortunate feature of the very early TV set that I had. Probably that type of transformer has not been sold for many years. A transistor version would be possible to create, using a more current flyback transformer, and I have seen published circuits for that version. And a stereo audio amplifier for the X and Y deflection would work, although the waveform would not be accurate. But how accurate does an entertainment device need to be??
 

Thread Starter

Externet

Joined Nov 29, 2005
1,957
:D Done !. Am happy, it works. Removed all camera switching and video board and hooked RCA jacks to disconnected deflection windings. Fed with speaker level audio and niiiiice ! I have my old toy again :)
May take a short video later.
Decided to do it with the cameras surveillance monitor as in image 3. The 3 CRT RGB I have canibalized from a projector TV lack a cabinet, (as in image 1) and are too big to become a toy. Put a temporary shelf next to my stereo, and perhaps will add a dedicated small stereo amplifier some day.

Too sunny bright room, but some trace barely visible :

1667582051834.png
 

Tonyr1084

Joined Sep 24, 2015
7,190
If you had a color tube you could designate the blue (pulsed by the amplitude) to recreate the high notes, green for midrange and red for bass signals.

The one I wanted to build but never got around to it consisted of a generated circular pattern where the dot appeared to move so fast it looked as a solid ring. Then modulate the amplitude in order to produce a series of dots. Depending on the frequency and the orbital rate high frequencies would produce many dots that may appear to slew left or right. Depending on the audio trac dots could move in both directions simultaneously. I know, I've done exactly that via mechanical means (LED on an old record mounted on a variable speed motor). You could literally read the music. Bass notes produced a few long dashes while higher notes produced shorter dashes or even dots, depending on the freq. My friends and I spent hours watching the light show while smoking stuff. (not advocating smoking of any kind)
 

atferrari

Joined Jan 6, 2004
4,671
Hi.
Original plan was using one of the CRTs salvaged from a rear projection TV like :

Then found among my other spider webs a vulgar surveillance CRT monitor. Perhaps will be simpler.
Want to feed real-time left audio to vertical and right audio to horizontal to produce lissajeous images, analog monochrome.



Have no schematic for the surveillance monitor. I can disable/remove the video cameras input circuitry, disable vertical and horizontal coil driving,... Been reading and looking at a few videos now... If you have ideas on how to feed audio channels to the deflection coils, please advise. Is it just amplifying to a level that deflects to the entire screen or there is more to consider ? Focusing, supplies, controls, biasing, HV untouched ?
Hola Miguel

Many years ago I managed to show text on my 10 MHz analog scope, obviously with a (PIC) micro, using X,Y inputs. To cancel the retrace effect l explored and learnt to use the Z input.

Software was fancy and convoluted... but worked like a gem employing a lot of tricks.

About 6 years later rewrote it from scratch building the display in a more logical, simpler and comfortable way.

The faster the micro, the better.

More characters (less spaces) slower the display.

If you are interested, schematic and software (18F family) available for the asking.
 

MisterBill2

Joined Jan 23, 2018
13,692
WOW!!! Generating vector text for a scope display! That is awesome indeed. My second experiment was feeding video from a VCR into an obsolete orange computer monitor. It actually did work, but it did not give a good picture. And how long ago did computers provide a monochrome composite video output??
But vector text on a scope screen is very impressive.
 

atferrari

Joined Jan 6, 2004
4,671
In the beginning I had to learn about timing, to obtain characters straight up, not bent. Left the retrace to be dealt with later.

NRR NO RASTER RON.JPG

Then I went for the Z axis. Looking better.

SANY8655.JPG

St George.JPG
 

Thread Starter

Externet

Joined Nov 29, 2005
1,957
Works well but poor brightness. Will have to tweak something. I do not know why lines show dotted instead of continuous. Unable to attach my video.

1667607240158.png
 

MisterBill2

Joined Jan 23, 2018
13,692
The lines are dotted because the beam is switching off at some speed. That is probably related to the not being as bright as you would like. Possibly you have AC where it should not be!Maybe the bias on the intensity control grid is not right. There might be a connection between the intensity control grid and the heater. OR there might be ripple on the high voltage.
 

MisterBill2

Joined Jan 23, 2018
13,692
Once again, the very first thing to check is the heater connection of the CRT. What is clear is that the beam is being switched off and on at a regular interval, most likely the mains frequency.
Aside from that the intensity is quite low, meaning that some of the CRT voltages are not correct. So checking voltages and connections should solve the problem.
OR, it may possibly be power supply ripple. What signals are being applied for the trace shown in the photo??
 
Top