# television to oscilloscope

M

#### m kinsler

Jan 1, 1970
0
I'd like to try building an oscilloscope from an old CRT monitor or TV
set. The purpose would be to display audio waveforms at one of the
science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe I'll
need an analog device to show things like the difference in the audio
waveforms of different musical instruments. The big screen of a TV
set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself with
is that the deflection yoke of a CRT is, or at used to be, part of the
high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any corners
on a waveform sent into a vertical deflection coil would be converted
into spikes.

So I'm lazy. Has anyone actually done this sort of thing and actually
had it work to any degree? Thanks.

M Kinsler

J

#### James Sweet

Jan 1, 1970
0
m kinsler said:
I'd like to try building an oscilloscope from an old CRT monitor or TV
set. The purpose would be to display audio waveforms at one of the
science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe I'll
need an analog device to show things like the difference in the audio
waveforms of different musical instruments. The big screen of a TV
set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself with
is that the deflection yoke of a CRT is, or at used to be, part of the
high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any corners
on a waveform sent into a vertical deflection coil would be converted
into spikes.

So I'm lazy. Has anyone actually done this sort of thing and actually
had it work to any degree? Thanks.

M Kinsler

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? N #### N Cook Jan 1, 1970 0 m kinsler said: I'd like to try building an oscilloscope from an old CRT monitor or TV set. The purpose would be to display audio waveforms at one of the science museums I work with; there's no calibration necessary. I've tried the various sound-card based 'scope programs available for the PC, and none of them show sufficient detail; I really believe I'll need an analog device to show things like the difference in the audio waveforms of different musical instruments. The big screen of a TV set would be helpful for demonstrations. I understand that this is a totally novel concept, and that Google doesn't yield a single thing on the subject except for the twenty-six thousand articles listed under "TV oscilloscope." But I must say that those plans seem either oversimplified or more theoretical than practical. The problem I keep concerning myself with is that the deflection yoke of a CRT is, or at used to be, part of the high-voltage circuit. Additionally, we run into the problem that a magnetic deflection coil is an inductance, and thus won't accurately show, say, a waveform that's not pretty darned sinusoidal. I would imagine that any corners on a waveform sent into a vertical deflection coil would be converted into spikes. So I'm lazy. Has anyone actually done this sort of thing and actually had it work to any degree? Thanks. M Kinsler 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. A #### Andrew Tweddle Jan 1, 1970 0 m said: I'd like to try building an oscilloscope from an old CRT monitor or TV set. The purpose would be to display audio waveforms at one of the science museums I work with; there's no calibration necessary. I've tried the various sound-card based 'scope programs available for the PC, and none of them show sufficient detail; I really believe I'll need an analog device to show things like the difference in the audio waveforms of different musical instruments. The big screen of a TV set would be helpful for demonstrations. I understand that this is a totally novel concept, and that Google doesn't yield a single thing on the subject except for the twenty-six thousand articles listed under "TV oscilloscope." But I must say that those plans seem either oversimplified or more theoretical than practical. The problem I keep concerning myself with is that the deflection yoke of a CRT is, or at used to be, part of the high-voltage circuit. Additionally, we run into the problem that a magnetic deflection coil is an inductance, and thus won't accurately show, say, a waveform that's not pretty darned sinusoidal. I would imagine that any corners on a waveform sent into a vertical deflection coil would be converted into spikes. So I'm lazy. Has anyone actually done this sort of thing and actually had it work to any degree? Thanks. M Kinsler 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 S #### Sam Goldwasser Jan 1, 1970 0 m kinsler said: I'd like to try building an oscilloscope from an old CRT monitor or TV set. The purpose would be to display audio waveforms at one of the science museums I work with; there's no calibration necessary. I've tried the various sound-card based 'scope programs available for the PC, and none of them show sufficient detail; I really believe I'll need an analog device to show things like the difference in the audio waveforms of different musical instruments. The big screen of a TV set would be helpful for demonstrations. I understand that this is a totally novel concept, and that Google doesn't yield a single thing on the subject except for the twenty-six thousand articles listed under "TV oscilloscope." But I must say that those plans seem either oversimplified or more theoretical than practical. The problem I keep concerning myself with is that the deflection yoke of a CRT is, or at used to be, part of the high-voltage circuit. Right. So you need either to substitute an inductor to keep the HV happy, or a separate yoke. Additionally, we run into the problem that a magnetic deflection coil is an inductance, and thus won't accurately show, say, a waveform that's not pretty darned sinusoidal. I would imagine that any corners on a waveform sent into a vertical deflection coil would be converted into spikes. So you turn the yoke around and use the vertical for the timebase. So I'm lazy. Has anyone actually done this sort of thing and actually had it work to any degree? Thanks. 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. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. B #### Bob Urz Jan 1, 1970 0 m said: I'd like to try building an oscilloscope from an old CRT monitor or TV set. The purpose would be to display audio waveforms at one of the science museums I work with; there's no calibration necessary. I've tried the various sound-card based 'scope programs available for the PC, and none of them show sufficient detail; I really believe I'll need an analog device to show things like the difference in the audio waveforms of different musical instruments. The big screen of a TV set would be helpful for demonstrations. I understand that this is a totally novel concept, and that Google doesn't yield a single thing on the subject except for the twenty-six thousand articles listed under "TV oscilloscope." But I must say that those plans seem either oversimplified or more theoretical than practical. The problem I keep concerning myself with is that the deflection yoke of a CRT is, or at used to be, part of the high-voltage circuit. Additionally, we run into the problem that a magnetic deflection coil is an inductance, and thus won't accurately show, say, a waveform that's not pretty darned sinusoidal. I would imagine that any corners on a waveform sent into a vertical deflection coil would be converted into spikes. So I'm lazy. Has anyone actually done this sort of thing and actually had it work to any degree? Thanks. M Kinsler 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 J #### J. T. Laurie Jan 1, 1970 0 that's what I'm trying to do though I'm trying to do it just for the hell of it. J #### Jim Yanik Jan 1, 1970 0 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?

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
For that you get calibrated graticule,switchable calibrated gain,reasonable
triggered sweep.

C

#### CJT

Jan 1, 1970
0
m said:
I'd like to try building an oscilloscope from an old CRT monitor or TV
set. The purpose would be to display audio waveforms at one of the
science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe I'll
need an analog device to show things like the difference in the audio
waveforms of different musical instruments. The big screen of a TV
set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself with
is that the deflection yoke of a CRT is, or at used to be, part of the
high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any corners
on a waveform sent into a vertical deflection coil would be converted
into spikes.

So I'm lazy. Has anyone actually done this sort of thing and actually
had it work to any degree? Thanks.

M Kinsler

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.

C

#### CJT

Jan 1, 1970
0
Bob said:
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.

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

B

#### Bob Urz

Jan 1, 1970
0
CJT said:
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.

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

M

#### m kinsler

Jan 1, 1970
0
One question that comes to mind is why you don't just use a real
Mostly because the screens are quite small.
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.

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

J

#### James Sweet

Jan 1, 1970
0
m kinsler said:
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.

F

#### [email protected]

Jan 1, 1970
0
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° 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.

B

#### bz

Jan 1, 1970
0
I'd like to try building an oscilloscope from an old CRT monitor or TV
set. The purpose would be to display audio waveforms at one of the
science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe I'll
need an analog device to show things like the difference in the audio
waveforms of different musical instruments. The big screen of a TV
set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself with
is that the deflection yoke of a CRT is, or at used to be, part of the
high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any corners
on a waveform sent into a vertical deflection coil would be converted
into spikes.

So I'm lazy. Has anyone actually done this sort of thing and actually
had it work to any degree? Thanks.

M Kinsler

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.

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

M

#### Marra

Jan 1, 1970
0

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.

--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

[email protected] remove ch100-5 to avoid spam trap

C

#### Chris Jones

Jan 1, 1970
0
m said:
Mostly because the screens are quite small.

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

Chris

Z

#### z

Jan 1, 1970
0
I'd like to try building an oscilloscope from an old CRT monitor or TV
set. The purpose would be to display audio waveforms at one of the
science museums I work with; there's no calibration necessary.

I've tried the various sound-card based 'scope programs available for
the PC, and none of them show sufficient detail; I really believe I'll
need an analog device to show things like the difference in the audio
waveforms of different musical instruments. The big screen of a TV
set would be helpful for demonstrations.

I understand that this is a totally novel concept, and that Google
doesn't yield a single thing on the subject except for the twenty-six
thousand articles listed under "TV oscilloscope."

But I must say that those plans seem either oversimplified or more
theoretical than practical. The problem I keep concerning myself with
is that the deflection yoke of a CRT is, or at used to be, part of the
high-voltage circuit.

Additionally, we run into the problem that a magnetic deflection coil
is an inductance, and thus won't accurately show, say, a waveform
that's not pretty darned sinusoidal. I would imagine that any corners
on a waveform sent into a vertical deflection coil would be converted
into spikes.

So I'm lazy. Has anyone actually done this sort of thing and actually
had it work to any degree? Thanks.

M Kinsler

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.

M

#### [email protected]

Jan 1, 1970
0
Mostly because the screens are quite small.

I've tried that, and the waveforms are just not detailed enough to be
very useful.

What does that mean? We can only help if you explain the problem.
One looks a lot like another,

are the waveforms in fact similar, or quite different?
and the response is far
too slow.

Please explain. PC sluggish, scope bandwidth too low, what?
I may be using the software incorrectly, but I've had
little luck over several tries.

M Kinsler

NT

M

#### [email protected]

Jan 1, 1970
0
Mostly because the screens are quite small.

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

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