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View Full Version : TV to Oscilloscope >Gasp! Sorcery!<



bbcmicro
May 31st, 2006, 03:25 PM
I've wondered on and off about getting an oscilloscope, for many deep and practical reasons:

1) So I know if something is on or off
2) because they look nice.

This is not enough reason to justify buying one that I cant afford anyway, BUT! I do have an ace up my sleeve, in the form of a 5" portable B&W television! I know that there is some tinkering about to be had, but what is your advice, and where can I find a good clear guide? The only bit i'm concerned about is the circuit and actualling getting around to sourcing the parts in my small and lazy life.

DimensionDude
May 31st, 2006, 03:33 PM
It can be done, but it's not easy. Just too many differences between a tv and a 'scope.

Have you looked into software that allows your computer to be used as an oscilloscope? I believe that the interface isn't too hard to construct, depending on which software you get.

Kent

atari2600a
May 31st, 2006, 03:34 PM
Ah, you Londoniese people with your alchemy & wizards & whatnot!

Seriously though, coudn't you just buy one & strip it of it's parts?

dongfeng
May 31st, 2006, 03:41 PM
Secondhand oscilloscopes are relatively easy to find for decent prices if you know where to look, but you'll get a pretty outdated one at the lower end of the market. I bought one for 25 during my University days as it was useful for the microprocessor work I was doing at the time. Since sold it though (for 25!), wish I hadn't.

The computer software version sounds interesting!

bbcmicro
May 31st, 2006, 03:44 PM
Londoniese?!?!

I'm from Manchester!

Were not all cloyingly cheerful cockney shoe-shines, or at least I don't think so...

Yes, dog and bone, apples and pears and all that malarkey! and yes, the magical box makes squiggley lines! What kind of magicianry is this? Blasphemy! etc. etc.

I've never seen one but I've never been looking I suppose.

Would the software version need a special card or just a cable with probes?

atari2600a
May 31st, 2006, 03:49 PM
Sorry man It was a joke!

Have you tried eBay?

bbcmicro
May 31st, 2006, 03:58 PM
lol, its ok.

I did have a look on eBay, 50+ for an old valve one, 100+ for anything in the last 30 years. At least last time I looked. I ought to look again.

DimensionDude
May 31st, 2006, 06:55 PM
I've seen various forms of software with various hardware requirements. Everything from using serial, parallel, or sound card inputs to separate A/D conversion boxes.

At the very least, I would want something that isolates the inputs from the computer lest it send a damaging voltage into the machine.

Are there any Army Surplus stores or auctions in England? I got a decent Hewlett Packard 'scope some years ago for $25. No probes, but it did work. Navy surplus, the last calibration sticker on it is from around 1973.

Kent

atari2600a
May 31st, 2006, 07:12 PM
It can be done, but it's not easy. Just too many differences between a tv and a 'scope.

Kent


Aside from the actual curcuitry, theyr'e not too different. Both use CRT's, which is basically a single beam of light hitting a screen at a point manipulated by an electromagnet. It shouldn't be to hard (if you use the pcb & components from an actual oscilloscope), the connector to the CRT is probobly the same, & the knobs can be replaced...

DimensionDude
June 1st, 2006, 04:49 AM
TV uses electromagnetic deflection, scopes use electrostatic deflection. The crt in a scope has the deflection plates on the inside, a tv crt has coils on the outside.

I've seen some sites on the web showing tv to oscilloscope conversions, they work ok at audio frequencies but not much higher. Also, if I remember correctly, getting it to work at all was a challenge.

For audio frequencies, I'd use a computer with a sound card.

Kent

DimensionDude
June 1st, 2006, 06:24 AM
I'm not trying to dissuade you, just let you know the realities so you don't expect too much.

Here's a link to get you started.

http://www.repairfaq.org/samnew/tvfaq/tvtoscope.htm

Kent

Terry Yager
June 1st, 2006, 07:47 AM
Yeah but, I wonder if an ol' scope could be modded to recieve TV signals...?

--T

DimensionDude
June 1st, 2006, 08:01 AM
Yeah but, I wonder if an ol' scope could be modded to recieve TV signals...?

--T

Soitenly! Nyuck, nyuck, nyuck! Oh, sorry, had a Curly moment. All you need is a tuner and sync generator. Most scopes have a Z-axis input to modulate the beam.

Kent

alltare
June 4th, 2006, 06:56 PM
DazyWeb Labs used to have a free computer scope program that worked pretty well on >1GHz computers ("DS-2002 PC Oscilloscope"). They have disappeared for some reason, but you might still be able to google their software.

nige the hippy
June 7th, 2006, 08:35 AM
BBCMICRO, check out...

1) RSGB radio rallies, usually less than half the price of EBAY (but 1/10000 the stuff!)

2) Electronics firms.. ie go door knocking at smaller firms. (I gave my last two scopes away, they were ancient, but still better than anything you could make). often firms will have old scopes that are slightly cranky, or not worth calibrating. and are just taking up shelf space. be DEAD polite, and ask for the cheif engineer, as most receptionists will just send you away as a spotty little oik. (I also got interesting summer jobs, filling in for people on holiday that way!)

good luck.

Twinhead
August 10th, 2006, 03:24 PM
Excuse me for Grammar errors, I am Dutch.

Well I have done it several times in the past...
Nice to tinker with those!!

It is a VERY CRUDE TIME FIXED scope which draws quite a load from the measured Object, but Hey, you DO get a waveform on the screen!
Lateron I was able to get an good MF Amplifier in the system to Unload the measurement.

Steps on how to do it:

-!!- ALL OF THE BELOW MUST BE DONE WITH POWER DISCONNECTED -!!-

01 Get a B&W television set which DOES still give a raster and a bright beam.
02 Get a deflection yoke from an identical unit (More of it later!)
03 Open the unit that you want to convert, and determine which are the HORISONTAL sweep wires (2) of the deflection yoke.
04 Cut those wires, ( NOT the connections with them!!) and solder them on the corresponding pins of the 2nd Yoke.
05 Get that 2nd yoke as far away from the CRT as possible (Lengthen the wires?)to reduce the influence, preferrably with the business end down / away from the CRT. (If long enough, park it somewhere outside the set.)
06 Loosen the clamp of the yoke on the CRT.
07 Rotate it EXACTLY 90 Deg. clockwise (CRT face facing away!) and reclamp it. (This will convert the vertical 50 / 60 Hz sweep into a Horisontal left-to-right sweep)
08 Solder 2 long wires on the previously empty made pins and led them extend long enough outside the cabinet.
09 Dim contrast and brightness and turn the set on. (Replug the power)
10 Turn the brightness up until you see a nice horisontal sweep.
11 Search for the variable resistor which is ment to stretch the pictuire (Sweep) vertically, and turn it until the sweep fills the whole sceen width.
12 Get a short cirquit proof frequency generator and connect it to the leads you just had soldered on the yoke.
13 Turn it on, play with waveforms, amplitude and frequencies and watch the fun!!!
14 IF you are lucky to find the variable resistor which determines the base vertical timing, (Rolling picture when set wrong in a working unit) you can unsolder it from the PCB and mount an equivalent Potmeter in the cabinet and wire that one up.
This will add some course frequency (timing) control.


IF you happen to have a precision symetrically amplifier of a few watts, solder an 8 Ohm 10 Watt resistor in series with the output and connect that to the set.
Then use the input to measure objects, preferrably inductivly coupled by an Impendance transformer which has > 10K Ohm on the primary to disconnect the grounding lead.

Well, Start rigging, and please sent feedback on how things goes!

Victor.

Twinhead
August 12th, 2006, 02:24 AM
Yeah but, I wonder if an ol' scope could be modded to recieve TV signals...?

--T

Well Terry, it IS feasable!

It is reverse as what the topic is, but by visiting THIS (http://www.electronixandmore.com/project/14.html) link, you will see that it is possible, and done.
Now only to get (temporarly) rid of that grid...

Victor.

BradN
August 26th, 2006, 11:23 PM
For audio frequencies, I'd use a computer with a sound card.


Bonus points if you can remove the DC filtering from the sound card - otherwise you'll have a hard time measuring DC voltages, and I'm guessing lots of waveforms will end up shifted because of it.