television to oscilloscope

It can be done, but the performance is pathetic compared to that you can get from a $10 Eico or Heathkit oscilloscope. Old basic scopes are SO cheap now, why bother trying to convert a TV?

When I worked in a college we did this and also a TV diplay - audio spectrum analyser. A lot of the functionality of a scope is the front controls of mS/cm , amplitude control for various inputs. Cross mix/gate the sweep out and an internal 'y' signal of a basic scope with a sync generator/ramp for feeding into a TV / projector TV. For spectrum analyser a series of bandbass filters with S&H outputs polled across the bands. I remember how saw-toothy a bowed violin, stick-slip, waveform looks and graphically showing the difference between white noise and pink noise as a spectrum display.

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I built one of these about 20 years ago based on a kit in Electronics Australia. Basically a complete time wasting exercise. With a sound card and a PC and one of several sound analyzing pieces of software you get an out of this world result, compared to even old sound/vibration analysis hardware from HP or other makers. If you need a TV screen just to show the class then use a video card with TV capability or one of them modern plasma/LCD flat screens with VGA in.

regards Andrew

Right. So you need either to substitute an inductor to keep the HV happy, or a separate yoke.

So you turn the yoke around and use the vertical for the timebase.

As others have noted, this is certainly not worth doing to obtain a useful instrument.

For a science museum display, what would be the point? Size or just showing that it can be done?

If you need to cover a large area, just get several old scopes. :)

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As others have said, the direct conversion is futile. Now, if you a scavenger on the cheap.

ingredients:

1) old cheap O scope 1) old cheap large TV. 1) old camcorder with tape section broken so you can get it cheap.

directions:

Put signal into the scope as usual point video camera at the scope. (make a hood to shield outside light) use video camera output to feed the tv.

Bob

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"James Sweet" wrote in news:Qh3fi.573$t95.469@trndny01:

You could pick up a used TEK T922/932/935 or TEK 442(T935 in a rackmount!) for well under $100 on Ebay. That's 15Mhz-35Mhz,simple circuitry,easy to repair,no TEK-made ICs. For that you get calibrated graticule,switchable calibrated gain,reasonable triggered sweep.

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I did it in 1968 +/- as something to liven up parties. I found two TVs with the same chassis and added the yoke and vertical section from the second one to the first. I hooked the original horizontal section to the horizontal windings of the extra yoke so I'd have HV. Then I hooked the extra vertical section to the part of the yoke that was originally part of the HV section. In my particular case, the horizontal and vertical sections of the yokes weren't terribly different, which helped.

I hope that makes sense. In my application, I didn't need a sweep generator -- I was using it as an XY display of the two stereo channels against each other. And frequency response wasn't critical. It made a pretty psychedelic display.

Eventually (maybe fairly quickly) the center of the tube will burn unless you add some circuitry to blank the beam when it's centered.

By the way, in 1968 it was black-and-white. You might run afoul of the safety circuitry in a color set.

One question that comes to mind is why you don't just use a real oscilloscope.

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You better find a scope with a high persistence phosphor if you want to try this way.

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CHeap alternative method #2

Get cheap old windows 98 machine for next to nothing get cheap old 17" VGA monitor or such get shareware oscilloscope software on the net.

Then use the soundcard on the computer to display waveforms in the audio range.

Bob

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Mostly because the screens are quite small.

I've tried that, and the waveforms are just not detailed enough to be very useful. One looks a lot like another, and the response is far too slow. I may be using the software incorrectly, but I've had little luck over several tries.

M Kinsler

The problem is likely lack of triggered sweep, something you really need a real scope for.

i have managed to convert an old PC monitor into a very crude oscilloscope. it does show quite a good waveform but square is a bit pointy. but otherwise is quite good for an old 640x480 15inch CRT monitor

depending on the intended use it may be sufficient. all you need to do is rotate the yoke coils 90=B0 either way so that the vertical deflection coils are now horizontal. disconnect the now vertical (horizontal) coils and attach to either an amplifier (adding resistors to match output load impedance of the amp) or direct input if the voltage is high enough and will handle inductive load resistances below 1 ohm or so. also the CRT control board may not like having no horizontal coil so if you can attach an inductive load around the same resistance as the deflection coil (i used a 12volt car battery transformer secondary winding) to the old coil connectors should make it turn on. you'll need some kind of oscillator (like a NE555 timer) to produce a triangle/saw tooth wave into the (now) horizontal coils to adjust the timebase frequency. or find a way of adjusting the said frequency on the board and depending on what needed adjusting either put a rotary switch with various values of the component or an adjustable resistor. I'm guessing it will either be a resistor capacitor oscillator or something else.

m kinsler wrote in news:1182580014.502103.44600 @g4g2000hsf.googlegroups.com:

You might try a different approach, there are A to D capture devices that will turn any computer into a scope.

Cheap monitor, cheap computer, A to D capture device and you have a scope that will show detail and can be seen by the class.

You can also feed the video from the computer into a modulator and put it onto your large screen or projection tv.

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Buy a cheap scope.

The Telequipment D83 has a nice (relatively) big screen.

Chris

Friend of mine did it in high school for the science fair. Worked OK, but very limited as to upper frequency. I have no idea what the actual modifications involved were.

What does that mean? We can only help if you explain the problem.

are the waveforms in fact similar, or quite different?

Please explain. PC sluggish, scope bandwidth too low, what?

NT

While I'm here I think you can rule out a converted tv tube on safety grounds. With such basic scopes there is nothing to stop deflection going off screen and heating a point of glass tll it softens and goes bang.

FWIW correct waveform was obtained by using current drive, but bandwidth is still lmiited. They were just crude tools for tinkerers that couldnt possibly afford a real scope.

NT