Introduction: How To: Make a CRT TV Into an Oscilloscope

Picture of How To: Make a CRT TV Into an Oscilloscope

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.

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

Step 1: Identify Wires

Picture of 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

Picture of 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 3: That's It

Picture of That's It

Really, it's an oscilloscope now.

Step 4: How to Use It With Music

Picture of 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.


SteffenV3 (author)2017-12-15

This is so cool, I found this old tv years when clearing out a storage room for my old employer. I'm gonna try to do this, but I'm very new at soldering, so I think I might try another project first. This one has a jack input behind for receiving signals. Maybe I could reroute it for the oscilloscope input?

MaestroP1 made it! (author)2017-11-13

Best guide to get this crappy effect done.
I had a spare tv and it worked like a charm, I've used the internal audio amplifier (was connected to some cheap 8ohm speaker) to get the signal, then i reconnected with a pot the speaker so I've got audio and video with different volumes.
While soldering the speaker some solder fell on the color processor ic and I've got some funny effects - rainbow line! Now I've cleaned it but it may be worth circuit bending that one (it pissed me off that i had lost the intensity information from the video input so i removed the solder)
Great toy. Fast as hell to build!
Thanks, wasn't believing that it could be that easy.

Tip based on what i saw:

I found in mine trimpots on the gun for the different colours and saturation. On the board there where trimpots for x and y scaling as well one for dark signal level
The power to the gun had 2 pots one for intensity and one for focus, becareful with intensity, you may generate too many xrays and it's not healty.

Mixing a AV video signal and the hacked signal gives cool effects as the AV signal writes the intensity and regulates the frequency.

Having a too high AV signal gets some lighting like effects on screen. In my case the wave is violet. But if the signal peaks then the screen glows at its borders and a white out of focus line cuts the screen.

That looks great! I really like the color, and if I run across another old TV I think I'll have to look into what you've suggested; it sounds like there's a lot more freedom for experimentation than I thought.

8runo made it! (author)2017-05-02

Got some photos as well

Magnelectrostatic (author)8runo2017-05-04

Glad you got it, and with the full height of the screen too! Looks great.

8runo (author)2017-05-02

I nailed it second try. Really easy and fun nice instructable

WConrad23 made it! (author)2017-04-11

hi! I tried to make an Ossola scope with an old TV/radio, but I have run into some problems. Here's what the design looks like. Pls help!

I see a headphone jack and I can see some of the coil connections, but I can't quite make out where everything is going. Would you be able to sketch a diagram showing connections? In particular, any connections that you've changed, moved around, soldered/desoldered, etc.

GuillermoO12 (author)2017-04-02

hi! I've already done this with an old crt tv but I was wondering if it would be ok to connect the tv's own audio wiring to the coils so I can just input an audio signal (somewhere in the circuit) and use the tv's own amp to drive the coils, I haven't done it yet because I think it might be dangerous but what do you think?

I like the idea! If you find the speaker(s), it should lead you right to the TV's amplifier, and if it's an integrated circuit (a chip) you might be able to look it up online for more info.

There's always danger working inside the TV because of the high voltages. As for this specific modification, the amplifier is not designed to drive the deflection coils. This could potentially lead to excessive heating which, in the worst, case means fire! I don't think that's particularly likely, but if you try it, be safe!

Thanks! Yeah in fact I was able to input my own audio into the tv amp and hear ir through the speaker. So I'm gonna proceed now... I'll be posting images soon

Ctimekeeper made it! (author)2016-12-03

Need some help here! I followed your instructions to the T and ended up with the following. It reacts to music sort of like two spectrum anylizers placed back to back (bumping along with the music) the only difference was that i used speaker clips rather than a pair of old headphones.

From the things people have posted over the past few years I've learned that not all TVs are the same (unfortunately, I haven't quite learned in what ways they're different), so things seem to vary with the instructions here.

So, for yours, have you tried swapping around the horizontal coil (tried it on both the horizontal and vertical sweep-drives)? Mine only went fully across the screen for one of the 2 configurations; the other one performed better.

Let me know how it goes; from the looks of it you're really close!

Lola43210 (author)2016-04-28

Hi ..?
This is the third TV burnt !! ?
It was showing that line and then after 7 minutes suddenly disappear! it is happening every time
Why that does not work with me?
The TV is working but the screen is black.
The horizontal coil supposed to handle the 60hz what is the wrong ?
I even could not try that circuit you suggested ...

JasonP155 (author)Lola432102016-08-16

Try connecting a "dummy" coil to the disconnected output. Try to choose a coil of similar impedance to the yoke. (1-2mH, 5-10 ohms).

Next time try using a small black and white unit. The simpler the better.

Sorry I took so long to respond! And I'm sorry about all the TVs; that's too bad.

The TVs don't work at all any more? And does anything actually burn? Do any components inside look like they failed?

Moving the deflection coils shouldn't make anything change in a way that would break the TV

no problem
actually I finally did it! and I find out what was the problem
thank you very much for your help :) and your instructions.

Woohoo! I'm glad to hear that.

JasonP155 (author)2016-06-12

I am not surprised people are killing TV's. It is not uncommon for Large, color displays to have protection circuitry that shuts the system down in the event of a deflection coil failiure. When these things were new they were very costly and vulnerable to permanent damage from burn-in. Any one this worked well for no doubt noticed how intense the trace is at normal brightness. Normally that beam scans the whole frame. My advice is to find yourself a small black and white crt to work with. Early Macintosh computers (SE, Plus, SE/30, etc) are excellent for this. Very rugged.

As for the input, direct feeding the vertical yoke is awfully crude. In order for this to behave anything like a real scope from the signal's point of view, you need a buffer, an amplifier, and an impedance matching network. Otherwise referred to as the scope's vertical amplifier. If you don't know what that means or how to put that sort of thing together, if the TV you're working with has an audio input, I would recommend finding the wires leading to the TV's speaker, sending them to the vertical yoke, and putting your signal through the audio input. If you're using a monitor or sound is no good, you could also use any old stereo power amp that can drive low impedance speakers.

quinstructable made it! (author)2016-05-03

I used jerkey's suggestions and just rotated the coils and hooked the old horizontal coil to the speaker lines. This is intended for a brain-in-a-jar project so random wave patterns is just fine.

Sounds like a neat project!

Lola43210 (author)2016-04-15

I do all the instruction for 3 tv !!!

One of them dosnt work anymore
and the rest show that the herizontal line but when I contacted to the signal sources still show me that line

There is no wave shape. :(

What type of signal source did you use? It's possible that it wasn't strong enough. A good source to test with is a battery connected to a potentiometer. You can put the center pin of the potentiometer on one end of the vertical coil and ground the other, then you should be able to move the line up and down.

First I want to thank you

I am sorry if I am gonna bothering you
I want asking you
I don't think I get it !

I connected with my laptop and then my phone and I played some video on YouTube that had 20~3000 Hz
Is not enough ???

And you are suggest that I should to connect the v-coil with battery and potentometer just like that without a laptop ???

Not a bother at all! Your laptop or phone should work fine, was the volume turned up high?

And yes, no laptop. I've attached a crude image of the setup.

oh !!

thank you sooo much !!

I will try that and tell you what I got (:

Good luck! Hopefully we can figure this out.

It is me agin :)

It is ok if I choose a 9 volt battery ?
And what would you suggest for the pot ?
1 kohm good ?

Both of those should work, but you might want an additional resistor of 100 to 1000 ohms in series with the battery to limit its current. You can also just limit it by how far you turn the pot.

Now, this reply is getting a bit longer than I had hoped...but I think on my TV the vertical range was only about a volt, if even that, so I imagine a AA (or AAA or D) battery would also work fine, and with the 9V battery you might only have a small range on the pot that's visible on the screen. If the voltage goes too high or too low (negative) the line will disappear completely!

I'm also not sure what the resistance is in the coils (if you have an ohmmeter you can always measure it!) and I'm not sure how much current they can handle, which is why I recommended the additional resistor - to prevent the battery's full voltage from falling directly across the coil.

Naveen Chandra GuptaB (author)2016-04-14

I got an old CRT monitor can I use for above

which wire is best to extend the coil wires out of the cabin like any suggesions to use a Monitor cable etc.

Frequency limitations of this CRT oscilloscope

Any wire should work; it does not have to be something special.

The frequency limitations are vertical scan rate and the width, because we use the vertical coil-driver to drive the horizontal coil, and the width determines how much information we can get in each scan across the screen. We can measure the width as vertical bars, and effectively the number of bars multiplied by the scan rate is the sampling frequency. The highest frequency this will work for is less than half of the sampling frequency.

From this wikipedia article, a 1280 x 1024 TV would have a vertical scan rate of 89 Hz; admittedly, I do not know the resolution of my TV. Assuming is it 1280 x 1024 though, the middle portion that gets used is probably 1/3rd of the total width, or 1280/3 = 426.6 lines. Let's say, 427.

So the frequency limit is

(427 lines per scan) * (89 scans per second) / 2 = 19,001.5 Hz

I've never looked into this before, and I'm actually shocked. That's really cool! The upper limit of human hearing is near 20 kHz, so this covers just about everything you would find in music. At 19 kHz though, a sine wave would look more like a very thick vertical line. Still though, pretty neat!

CabeDueck (author)2016-02-08

I used an auxillary cable that my teacher found me. it was old enough.

Great! I'm glad it worked out

CabeDueck (author)2016-01-30

Hey, I really want to make this but all the headphones I've cut apart are too new! Could you let me know what kind of jack to buy? Thanks.

Yonatan24 (author)CabeDueck2016-01-31

What do you mean? What headphones do you have?

CabeDueck (author)Yonatan242016-02-01

The headphones that I use have tons of tiny coloured wires within them, not the three wires described.

Yonatan24 (author)CabeDueck2016-02-02

Are they by any chance those Nokia earphones with the big (wide) black connector?

I'm with yonatan24 on this one, I've never seen headphones that wouldn't work for this. It should be possible with any pair (especially a cheap one that you don't mind destroying). At the same time, if you want to buy the parts for it you could get a male audio jack and attach that to the TVs input.
(for example, this 3.5 mm audio jack
not that you would have to buy from that supplier - just as an example)

Yonatan24 (author)2016-01-31

Hi, I've added your project to the "Make Your Own Oscilloscope!" Collection

This is the link If you are interested:

Neat! Thank you

QuackHacker made it! (author)2015-09-08

great instructable. I just completed this on a 1988 Cosmo Communications 5" portable color TV. My only issue is that the right half of the signal image is out of focus! I've tried every adjustment save the ring tabs on the neck of the tube which are glued together.... Any ideas? Short clip attached showing the problem!

I'm sorry for this incredibly late response, and even more so because I don't have an answer. That's pretty interesting though. Mine would only display on a small rectangle in the middle of the screen, which I assumed is because the vertical coil wasn't meant to deflect the beam as much as the horizontal coil, but in your case that doesn't quite seem right because the beam isn't symmetric. It's like the right side of the screen is being swept over or refreshed too quickly. Even if that is the case though, I'm not sure what would cause it.

But if this project is still sitting out and you happen to have some magnets around, you might be able to deflect the beam away from that edge, and worst case magnets and CRTs always gets interesting! Let me know if you figure it out

Engineeringmaster106 (author)2014-11-14

Is there a way I can make it display a single transverse wave and not multiple... well whatever those waves are called. I don't want to settle for less and I really want to make this oscilloscope. If it's another circuit I can do with that. I know it's been three years since you last answered a question but can you help me out?

Thanks that helps a lot! I'll check out the video. And I was reading the first top comment and it said 3 years so I thought that would be the most recent one. Thanks again!

There's a response from ten months ago if you look further down! But I am pretty sporadic with response times...
So if I understand correctly, the problem with this is that there will be multiple waves visible on the screen at once?
I think it's related to the refresh rate of the screen - the electron beam moves across the screen at some finite rate, over and over again. Say that we put in an audio signal thats a higher frequency than the beam's frequency; now the beam wants to move up and down faster than it moves sideways, so it starts drawing weird looking stuff. This guy made a scope the same way, , and gets some really nice looking - low frequency waves at the beginning.

But that could also be completely wrong! Maybe the old waves haven't faded out by the time the next one is drawn on, which would be a property of the phosphor coating on the screen. Or maybe something else! If you have any more questions let me know, and good luck!

Reallunacy (author)2011-06-18

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.

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.

shomas (author)Magnelectrostatic2014-06-10

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.

rainman002 (author)Reallunacy2011-12-15

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.

app0 (author)2011-03-30

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?

About This Instructable




Bio: An electrical engineer who likes to make things.
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