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tv vs. oscilloscope

A long time ago I asked about what one would have to do to convert a TV into an oscilloscope. I can't find my original posting on dejanews but my recollection is that people told me one can't really do that with a TV. I was thinking about it recently and realized that I didn't really understand the reasons which, according to my vague recollection, had something to do with the electron beams in oscilloscope CRTs being controlled by magnetic fields while those in TV CRTs being controlled by electric fields. For one thing, I'm not sure whether this refers to a difference in the coils used or whether it refers to a difference in the construction of the CRTs themselves.

One idea I had for converting a TV into a really lousy oscilloscope is based on something I read once in an electronics magazine in the late

1970's and tried out (this isn't safe, e.g. once I did it and inadvertently shorted the whole thing out with a rather large bang but no explosion): (1) Open the back of the (b&w) TV and unplug the CRT tube. (2) Carefully slip the yoke off the tube without cutting any wires. (3) Take another TV and clip the wires to its yoke and remove it from the TV. Connect its wires to another signal source, such as the speaker wires from a record player. Then slip this coil onto the yoke of the first tv. (4) Plug the CRT tube from the first TV back in.

Then one turns on the first TV and the record player. When I played Rimsky-Korsakov's Scheherazade the white dot in the center of the screen spiraled around the screen in interesting ways.

I think that if one can do that, one can at least do some of the simpler things one can do with an oscilloscope by building various circuits and connecting them to the lead wires to the coil of the 2nd TV, or maybe by programming a computer to supply signals to those leads.

Since one doesn't have any control over the circuits of the first TV, one can't do stuff like turn the electron beam on and off, to keep the dot from leaving a trail if one wants it to jump around to various places on the screen.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.
Reply to
Allan Adler
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No you cant do that. There are too many reasons to list, just forget the idea.

Reply to
cbarn24050

Since posting this, I did a google search for: converting tv oscilloscope and found some information, including a description of what one person managed to build at:

formatting link 

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.
Reply to
Allan Adler

Many years ago Elektor Electronics magazine published a design for an adaptor box to display oscilograms on a regular broadcast display.

Reply to
ian field

It is fairly simple to cause interesting patterns to be displayed on a TV screen, but it is quite another thing to obtain an oscilloscope type display. In the 60s, a lot of circuit diagrams were published for displaying games like Pong, and music.

If you have studied TV at all, you should be aware the TV uses a raster scan. Each horizontal line is 62.5 microseconds in duration. If I want to place a vertical line in about the center of the screen, on line 250 I will put a brief (1 uS) voltage onto the cathode of the picture tube at about 32 microseconds into the horizontal scan. I will repeat that on subsequent lines for as many lines as it takes to make the line as tall as I want it. I may use 20 horizontal lines to describe my vertical line. My vertical line Is actually a result of *intensity modulating* the cathode of the picture tube. The vertical stage of the TV just moves the horizontal lines vertically.

In a basic oscilloscope, I can display a vertical line during a single horizontal sweep, because a voltage applied to the vertical channel drives the beam up or down depending on the polarity of the voltage. If I set the Horizontal sweep to 62.5 uS, and put a 1 uS pulse into the vertical channel, I will see the "line" but more importantly I will see it isn't a line at all, but a rectangular pulse that goes vertical and stays there for 1 uS, and then falls back to the baseline.

With this basic difference between a scope and a TV, you should see not to expect too much from a converted TV.

Don

Reply to
Don Bowey

Yes, you can do that, it's just complex.

Don

Reply to
Don Bowey

Still have the articles: RADIO ELEKTRONICA 1973-11 and 12.

I don t have a scanner,and the language is Dutch. For eye candy connect left and right loudspeaker output of a stereo amp to the coils.(Disconnect coils from main board) To avoid burn in you should make sure that you always apply signal,and adjust to a rather low brightness. The coil resistance is vert:~40 ohm, hor: ~4 ohm. The article advises to use a spare set of coils, connected to the mainboard to ensure proper operation of the TV electronics.

For use as a low frequency scope you have to build current output stages,and your frequency range is limited.

Also you can combine a comparator and a video source,compare the input signal with a 64 usec sawtooth,and inject a small .2 usec pulse or the comparator output itself into the video signal. In this case no mods to the tv are needed, but just a video input(scart or s.video). the bandwidth can be rather high as in a sample scope. If you use a number of comparators/sawtoothes?? you can have a nice multichannel display. A few high gain sensors, and you have your own earthquake display system.

Also have a nice live insurance policy :) ;)

Have fun and be careful.

Reply to
Sjouke Burry

I think that's the best answer, involve a computer wit an ADC. then you can have the TV scanning normally and use the computer's video hardware to produce the image.

Bye. Jasen

Reply to
Jasen Betts

I rcall in my days before I could "afford" a scope, articles in magazines regarding converting a TV into an O-Scope. I may even still have such articles. Question now is - WHY? Half decent and decent scopes are had by the dozen on E-Bay or most any Hamfest. Many are cheap enough that if you get a year out of it, you've gotten your monies worth. I've picked up some really decent scopes at liquidations for $50 a pop.

clfe

Reply to
clfe

In data Sat, 17 Jun 2006 15:19:35 +0200, Allan Adler ha scritto:

thanks for the infos, i tried this with an old philips 14 inch set and saw a green line...

--
Inty.Evolution
intiglietta@email.it -> per email normali e con immagini Jpeg
Reply to
Inty XP

There are a number of sites on Google that supply the Software to drive a sound card that uses the computer monitor as an output for a Audio Frequency range oscilloscope.

That is unless you really enjoy Smoke and Lightning.

You could avoid most of the Lightning by using a LCD Display . If you did that, you might as well consider going the Sound Card route.

If all else fails I would sell you an ancient Heathkit IO12 oscilloscope. for $US 25.00 + S/H (~$25.00) from Saskatchewan, Canada.

There are any number of used scopes for sale on Ebay for Under $100, so building your own is a No-Brainer, especially when you consider you really need a Scope to troubleshoot and test your creation.

Yukio YANO

Reply to
Yukio YANO

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