Instructables
This is the simplest possible way to make a CRT (cathode ray tube) TV into an oscilloscope, it can be done in about half an hour.

Supplies
-A CRT TV (color may work, but I'm not sure)
-Some wire
-A soldering gun
-Rubber gripped pliers (for safety)
-A screw driver
 
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Step 1: Identify Wires

After undoing all screws remove the cover from the TV.
Inside wrapped around the CRT are two coils of wire, one controls the vertical deflection of electrons, the other controls the horizontal deflection.
Find where these coils of wire attach to the circuit board, and desolder one coil.
Place the cover back on the TV(for safety) and plug in and turn on the TV.
If you see a horizontal line, you desoldered the vertical deflection coil.
If you see a vertical line, you desoldered the horizontal deflection coil.

Step 2: Placing Wires

Desolder the vertical coil if you haven't already and attach extra wire to the vertical coil, this will have to be long enough to come out of the TV so you can attach a voltage source.
Now desolder the horizontal coil, and solder it to where the vertical coil was.

Step 4: How to use it with music

I use mine to watch the waves created by music from my mp3 player
First take an old pair of headphones and cut one off, then strip away some of the insulation.
Now you should have multiple exposed wires, one will be slightly thicker than the others and wll have a thin coating of insulation on it - scrape it off.
Attach this wire to one end of the vertical coil, and the small group of wires to the other end.
Now plug it into a sound source, remember your attaching your mp3 player (or whatever) to a giant coil of wire, and there's chance it could break.
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Reallunacy3 years ago
Is there a way to know what the max input for voltage is? I am needing an oscilloscope so that I can properly set the gains on my amp. I want to be sure it isn't clipping, but I want to be certain I am not going to just fry the unit once I do this.
Magnelectrostatic (author)  Reallunacy3 years ago
Frying it probably won't be a problem, the input just goes to a coil of wire so you would probably need to burn off the insulation for something to break.
But on mine anything over about 1 volt goes above the screen, so I'm not sure if it would be much help (I don't know much about amps).
Hope this helps.

Series resistors might help with more volts in the input signal. If the signal is clipping, add any one of following resistor, 10, 100, 1k, or 10k, ohms in series with the coil.

You might have trouble actually seeing the wave shape, as this does not do any sort of triggering or synchronization to keeps the waves in the same spot on the screen. To overcome that, you'd need to tune your amp-input to a frequency multiple of the scanning frequency of the screen (probably by trial and error).

In addition, the high inductance of the coils may affect the output from the amp. Maybe a voltage follower of sorts would help, but I'm not really sure.
app03 years ago
Hello, nice instructable!
But I want to make a multi-mode oscilloscope out of my old TV, so I can use it as a usual oscilloscope and as an X-Y oscilloscope.
How do i do that?
Magnelectrostatic (author)  app03 years ago
I'm really not sure....don't even know what that means actually, sorry I can't be more help.
That's me again here after a year lol, I finally found a TV that I want to use, but, do i really have to switch the horizontal coil to the vertical source, or i can just connect the horizontal one to the sound input and get a vertical line? Don't really feel like messing with HV stuff :p
Magnelectrostatic (author)  app02 years ago
I never thought of that. I tried hooking the sound input directly to the vertical coil and the distortion was awful.
Unless you have another plan for the tv your idea sounds like it's worth a shot (and if it works that would be really cool).
Also, just for the sake of info, the coils aren't the HV part. The only HV danger with this is that you have to stick your hands inside the tv to do any of this stuff.

I think a CRT's normal vertical sweep (picture frame) is 30 hz, and 525 horizontal sweeps per picture frame making the original horizontal sweep sweep 30*525=15,750 times a second. With the CRT's vertical sweep serving as the new horizontal sweep, a 600 hz signal will look like 20 wave cycles on the screen and a 1200 hz like 40 wave cycles.

On the other hand using 15,750 sweeps per second, will not display most audio frequencies well. A 600 hz single will look roughly look like 26 mostly horizontal lines moving to right (i think). But, If you want to inject a 60 khz single with a 15,750 hz sweep, it will look like 3.8 waves cycles.

OK so I killed the TV in process lol.
Then I got a Mac classic with a bad logic board.
In process broke its vertical sweep generator somehow
So now ended up with this:
http://www.youtube.com/watch?v=ye3nyxc_MOw
http://www.youtube.com/watch?v=F0i6A2QjdBw

This was before the generator died:
http://www.youtube.com/watch?v=Fn_st_sX9fw

So now it's basically an XY scope, just need some filters and a second amp for the second channel, currently coils are connected to a mono amp with one channel.
Thanks for the i'ble!
Magnelectrostatic (author)  app02 years ago
So THAT's an xy scope! It looks great!
Well, I just need a visualizer looking like a scope so if it looks like a sinewave or etc. but not precise thats ok lol.
I'll give it a try soon and post the result
mgingerich2 years ago
Great instructable! I did this to an old black and white TV, and it came out pretty cool, except that for some reason instead of a full horizontal line showing up there is only a point or half-inch line that moves up and down in proportion to the input signal. Is there a way I can fix this?
I got it a little wider, but is there a way to make the wave use the whole horizontal length? It only moves in the middle third of the screen
Magnelectrostatic (author)  mgingerich2 years ago
Personally I'm not sure, but I think this instructable is jsut what you're looking for
http://www.instructables.com/id/Fully-Functional-Television-Oscilloscope/
Yeah, that's the sort of thing I want. After playing with my TV's settings for a while I realized the problem isn't easily fixed. Since the up and down dimensions are quite small, the signal from the vertical wires (intended for the vertical coil) that goes to the horizontal coil has too small an amplitude. I intend to substitute a sawtooth oscillator in place of the vertical wires instead.
shomas mgingerich2 months ago

Alternately you could try rotating the coil 90 degrees on the CRT and reattach the original vertical feed, now serving as your horizontal feed, to the original vertical coil, now serving as your horizontal coil. Original being that which was before you made any changes. With the original vertical feed feeding the original vertical deflection coils, the feed is likely to drive the most power coil. Then you can adjust the original vertical potentiometer, now horizontal after rotating the coils, so that it further deflects the beam.

shomas mgingerich2 months ago

Many CRT's have potentiometers that you can adjust for the vertical and horizontal. Your old vertical is now your horizontal. If your lucky, yours might be labeled. I strongly suggest using a plastic screw driver when tweaking these.

tbriscoe123 months ago

This works great! Just don't expect your ipod or other small MP3 player to survive it. With the CRT monitor I used somehow I got some voltage coming back through the audio wire. I may have overlooked something but I don't think so. Great instructable though!

insistent5 months ago

So ive found the 2 vertical coil and cut the wires to get the horizontal line, but when i connect the 2 hozirontal wire to the 2 vertical wire from circuit, i get a small line like in the picture, but its burry and messy, if i plug them back to how they were, i get the long and bright horizontal line back, so i was wondering if i could just cut the 2 vertical wire and plug them to the amplifier instead of doing anything else?

satytree5 months ago

how to convert soket from 7 pin to osissiclope

Sleepy Tiger7 months ago

Hey, I just tried this with my friend, and it works, but we used an old emachines CRT moniter. As soon as we tried it for a little bit we smelled something burnning, when we messed with the wires to make sure they where secure we tried it again and got the same burnning smell. Not really sure what to do? Any sugestions on what it might be or maybe where it might have burned?

Magnelectrostatic (author)  Sleepy Tiger7 months ago
Have you tried it with the case open (be careful if you do!) to see if there's anything visibly burning?
And I'm guessing it happens without the audio attached? That source should have enough power to damage anything, so maybe the horizontal coil can't handle the power from the vertical supply. If you have an infrared thermometer (one of the non-contact ones) you could try measuring the temperature of the coil while it's running (and remember, don't touch anything!)
jj.inc7 months ago

something to control the wave width would be handy, I imagine someone who knows something about how those coils change the beam (ie not me) could rig up a simple arduino circut to control it, just for when you have a situation where instead of looking out sound, you are looking into the mhz spectrum.

questwilliams9 months ago
This is a very informative instructable. In the morning I plan to experiment with both axis's with a different song on each coil and a goodtimes dvd playing in the combo tv.
so I tried this, and I got to the point where I switch the wires but when I plugged in my ipod I got only a fast clicking noise, so I reconnected everything to normal and the clicking noise persisted. any suggestions?
Magnelectrostatic (author)  darkLordNihilus12 months ago
Is it an audible clicking noise?
And it comes from the tv even now that you've placed things back the way they originally were?
agis681 year ago
maybe i missed on the text but this is only for audio waveform analysis or also for any purpose.....ie...to check a tv
alex5551552 years ago
Could I just cut the wires instead of desolder?
I'm a noob at high voltage, and don't like desoldering.
Thanks!
Magnelectrostatic (author)  alex5551552 years ago
You can!
mysterion2 years ago
....tried this, turned on my tv it immediatly shorted out and turned off, reconnected the horizontal coil it worked.......tried it once more boom, some small capacitors started blowing :(
Magnelectrostatic (author)  mysterion2 years ago
Aw man...that sucks. Sorry about the tv.
please give more elaboated idea of making cro from black and white tv and also elaborate about making dual trace cro from the same.give an account as soon as possible.
ebuzztone3 years ago
On color TVs, is it possible to use the RGB colors to add color to the lines, so that for example the incoming sound determines the color of the waveforms? An idea would be to make an automatic switching circuits that switches between RGB combinations. Would that work?
Magnelectrostatic (author)  ebuzztone3 years ago
There must be some way. This http://electronics.howstuffworks.com/tv10.htm shows how color CRT TVs work, and the next page tells how they switch the colors (I didn't really understand that page).
So it's definitely possible, it's just a matter of how....
Awesome idea by the way.
R.A.T.M3 years ago
i need help i did what it said to do then i pluged the tv in and herd screeming like a cap charging then when i turend it on a loud pop happend now all the tv dose is scream
Magnelectrostatic (author)  R.A.T.M3 years ago
Interesting...are you sure you only touched the part of the circuit board where the coils are attached?
iv found out what happen i dont know howit happen i blew a transister the one that drives the fly back it wont let me post a pictur but right dow the middle and it wass preaty vilent
Magnelectrostatic (author)  R.A.T.M3 years ago
Weird, if you ever figure it out make sure to comment!
A speaker is just a coil of wire but that never broke anything...
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