Author Topic: Need of Guidance for purchase of equipment for video applications and learning  (Read 457 times)

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Offline therickaman

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Hello All,

Before I begin, I'd like to express my gratitude to anyone who at least reads this post and even more for people who extend their help.  My question is regarding the purchase of a cheap oscilloscope.  I'm not sure about what to purchase and what would help me the most.

To understand the question, I think it's necessary to know my background and future trajectory.  Currently, I am a hobbyist in electronics all self-taught.  I am a professional applied mathematician (PhD in Computational Mathematics) and I hope to soon have an electronic engineering job.  My dream job would be to design, prototype, and build complex electronic devices or ICs.  To be able to do this, I need to learn electronics.  So, I've taken to learning in my free time and I hope it won't take very long given my education in math.

I am to the point though that I feel like my studies are being held back because I don't have a bench oscilloscope to visualize signals.  I did receive an analog discovery 2 for Christmas though, but because I've never used an oscilloscope before using it for applied applications is difficult for me at the moment.
 I've played around with it though.  So, I need a recommendation for a good oscilloscope that will carry me through my studies but because I don't have a job...it really needs to be cheap, like lower than dirt cheap.  This problem I can probably find an answer to because I'm sure it has been answered before.

The problem though is that I've accepted a job consulting for a very small company and that involves analog video.  I can get a video waveform/vectorscope monitor extremely cheap, but as far as I know I can't use that for anything else but video.  I believe an oscilloscope will be able to view analog video signals just as well but does the benefits of a specialized device outweigh the usefulness of an oscilloscope at the moment?  If a video waveform monitor is the way to go will I be able to view all SD signals?  Are there any that can view SD and HDMI output that is very cheap?  If need be I can wait (just a few months) to get a video waveform monitor, assuming that using an oscilloscope I can view the lines of the frames.  I think I create a circuit pretty easily that will select the desired line and only output that line's signal for viewing.

If an oscilloscope is the best option, then how fast does it need to be to view video signals?  I'm not sure if the analog discovery 2 can view video signals and if it does, I'm not certain about how to do that...any ideas?  What type of oscilloscope will be best for me to learn with and will carry me through my self-studies?  Should I save for a $250 Rigol?  Can these things be rented online for the time being?

Thanks,

Rick
« Last Edit: March 27, 2019, 11:36:29 am by therickaman »
 

Online EEVblog

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You have a consulting engineering job and you have to save up for a $250 Rigol?  :-//

Any scope will have the bandwidth for analog SD video, but to be useful it will need a video trigger option.
Most modern scopes including the 1054Z have video triggering.

HDMI is a different beast entirely, and you need specialised high end (expensive) gear to look at HDMI signals properly, very high speed digital decoding that is way beyond even mid range level scopes. You are talking on the 5 figure price range here.
« Last Edit: March 27, 2019, 12:01:04 pm by EEVblog »
 
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Offline blueskull

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SD is easy, a Rigol can do it. HDMI is ridiculously hard.

HDMI is digital signal, without analog modulation (aka not AM/FM/QAM/etc.), so 1Hz BW=1bps.

At several Gbps data rate, you are looking at a many-GHz scope.

Standard HDMI (non-MHL) has 3 TMDS data pairs. At 1920*1080*60fps*24bpp, we are talking about 3Gbps.

That is 1Gbps per TMDS pair, and that's when you're lucky. If you work with mobile devices, they may only have one lane, so you are expected to decode 3Gbps on a single data pair.

To reliably sample something without a synchronized clock, you need at least 2x the data BW as sample rate, so you are looking for a scope with:

1. 3GHz+ bandwidth (5GHz is the nearest common value)
2. 6Gsps+ sample rate (10Gsps or 20Gsps are nearest common values, modern scopes are no longer available in 10Gsps, so 20Gsps is what you can get)

That will cost you a lot. Not only the scope, you need high end decoding tools and active probes. Expect $50k minimum, and that's on a good day.

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That being said, my recommendation is to go with an FPGA board with HDMI input, and trust the signal source and cable to give you good signal quality.

If you are into cable or layout performance testing, consider a BERT or TDR or VNA.
 
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Offline chris_leyson

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You already have a useful digitizing scope, Analog Discovery II. It might be 20MHz bandwidth or so but that is good enough for SD analog video, add a sync seperator and a counter and you can view any line if you need to although I never found that feature was really very useful. If you are working on legacy NTSC/PAL/SECAM signals there are a still a few chips that will decode SD signals, TVP5150AM1-EP1 from TI is still active but probably not for long.
HDMI, well that's a completely different ball game.
 
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Offline therickaman

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You have a consulting engineering job and you have to save up for a $250 Rigol?

I apologize, I was not very clear about that.  I'm currently a freelance consultant and what I mean by that is individual companies can hire me to solve a problem or receive guidance on how to solve it.  Usually, it means that a company needs something built and I go about building it in a set amount of time.  After it's finished, I have no other ties to the company.  I've been hired to build something for a company, but the company isn't in a hurry for it to be made and doesn't need it until close to next year...thus, they haven't paid anything yet.  I'm working on a couple of projects and won't be able to purchase anything for myself that's large until finished.

Thank you for everyone's comments.  I'll reply as soon as I can.
 

Offline 0culus

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Another thing that you could do to keep your scope costs lower while still having more bandwidth at your disposal is to get a decent spectrum analyzer and use the 21.4 MHz IF out that most of them have to downconvert signals into a band any entry level 50-100 MHz scope ought to be able to handle nicely. I plan to do this myself as oscilloscopes with enough bandwidth for the RF bands I want to work in are prohibitively expensive to say the least. Bandwidth of the IF out might be a limitation...be sure to read datasheets!

If you're willing to do some repairs you might be able to score one of the portable HP 856x series instruments for not terribly much money. Here's one that is being advertised as having issues: https://www.ebay.com/itm/HP-8561A-6-5-GHz-RF-Spectrum-Analyzer-NEEDS-REPAIR/232752180687

If you're willing to spend some time diagnosing and repairing (both this forum and the HPAK mailing list on groups.io are great resources for this) you'll have yourself a nice little spectrum analyzer that's not a total boat anchor.
 
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Offline therickaman

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Looks like HDMI is out of the question unless I use the FPGA option as discussed.  I'm still wondering what the usefulness of a video waveform monitor is though.  Are there things that that device can do that an oscilloscope cannot?  I'm assuming that they have more functionality than an oscilloscope, since otherwise why were they made in the first place? 

Regarding the analog discovery 2 that I own, I'm slowly getting the hang of using it and that's only because I bought the BNC adapter.  I really like the analog discovery 2 and it has a lot of useful tools, but one issue that I have is that it isn't "bench friendly".  What I mean by that is, at my work table I have my soldering station with vice and third hand, various other equipment, stuff from ongoing projects, etc.  The analog discovery 2 has quite a number of wires coming from the device and to operate it must be connected to a computer.  One can argue that a bench oscilloscope will take up about the same amount of space as the AD2 with a computer attached, but the oscilloscope has fewer wires. Furthermore, with a computer at the worktable...I'm tempted to surf the net instead of work.  :(

I've been thinking about connecting the AD2 to a beagle bone black with a small touchscreen monitor.  That may solve some of the issues I have with it, but I'd still like to own a regular oscilloscope eventually.

If you're willing to spend some time diagnosing and repairing (both this forum and the HPAK mailing list on groups.io are great resources for this) you'll have yourself a nice little spectrum analyzer that's not a total boat anchor.


I really don't mind diagnosing and repairing equipment.  Thank you for the suggestion and I'll look into this possibility more.  IMO, the device you recommended though is quite expensive for it to be broken.  I could buy a pretty nice oscilloscope for that price, but I see what you're saying.  I'll keep that in my hat for the future.
« Last Edit: March 27, 2019, 06:42:11 pm by therickaman »
 

Online nctnico

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IMHO you should first clarify why you want to measure those signals. What problems do you need to solve?
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Keysight DanielBogdanoff

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Like others have said, HDMI requires some series equipment. There are a number of rental options out there for scope + probe + HDMI compliance/testing options, and if you need it you can bake in the rental cost to your consulting fees.

However, you'd want to be very sure you have the right know-how before going down that road.

At some point, if you continue to do electronics consulting, you'll need more than the AD2. But, if it works keep using it until it doesn't. A good best practice that I've seen from consultants is to set aside a % from your jobs to save up/cover equipment purchases and calibrations.
 

Offline borjam

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Looks like HDMI is out of the question unless I use the FPGA option as discussed.  I'm still wondering what the usefulness of a video waveform monitor is though.  Are there things that that device can do that an oscilloscope cannot?  I'm assuming that they have more functionality than an oscilloscope, since otherwise why were they made in the first place? 
The "classic" video waveform monitor is basicly an analog oscilloscope with the right presets so that you don't need to fiddle with the parameter.
 

Offline borjam

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Like others have said, HDMI requires some series equipment. There are a number of rental options out there for scope + probe + HDMI compliance/testing options, and if you need it you can bake in the rental cost to your consulting fees.
That reminds me of a fight with IBM about faulty SAS3 controller with a subtle problem. What equipment do I need to diagnose a problem that sometimes corrupts data every 100 GB written more or less?  :-DD :-DD

(I told them: send me the scope and I will prove it to you, but I get to keep it)
 

Offline therickaman

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In a sudden turn of events, I purchased two oscilloscopes for the decent price of $80ish dollars.  One is a tektronix 11402 and a hitachi v-660.  I know for a fact that I'm going to end up selling one of these, I just haven't decided which one.  Usually, when I know I'm going to sell a used item I always sell the item in better shape than I found it in.  More than likely whenever I receive the two oscilloscopes I'll change out the caps if they need it, fix any issues I find, buy the original user manuals, add probes, fix power supply if needed, and try my best to restore the casing of the body.  If I can recoup my losses and make a little bit of cash, I'll sell both and get a newer oscilloscope.

Any suggestions on which oscilloscope I should keep for myself?  I believe the tektronix one would probably be the best, but maybe I'm wrong.
 

Offline 0culus

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If the 11402's CRT is in good shape and you feel like any other repairs are within your capabilities, I'd keep it. It's probably among the first digital scopes though (mid 1980s according to tekwiki http://w140.com/tekwiki/wiki/11402), so it will have drawbacks over modern ones such as sample depth. Up to 8 vertical channels with 2 independent timebases, though.
 

Offline rstofer

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To understand the question, I think it's necessary to know my background and future trajectory.  Currently, I am a hobbyist in electronics all self-taught.  I am a professional applied mathematician (PhD in Computational Mathematics) and I hope to soon have an electronic engineering job.  My dream job would be to design, prototype, and build complex electronic devices or ICs.  To be able to do this, I need to learn electronics.  So, I've taken to learning in my free time and I hope it won't take very long given my education in math.

At the undergrad level, about the hardest subject (in my view) is Field Theory and Maxwell's Equations where they introduce curl and divergence and the students' eyes roll back.

Differential equations will come up fairly early with R-C, R-L and R-L-C circuits.  Laplace Transforms are used all over the place and Fourier Series comes up quite a bit.  Obviously, all the lesser included subjects are also required.  You clearly have that stuff covered!

I have no idea what happens at the grad level, I did mine in computer hardware design and stayed well clear of analog circuits.  Why?  The math ...  To a math major it probably looks trivial but I struggled.  I succeeded, but I struggled.

But I took the courses in the pre-Internet days.  Heck, in undergrad we were using slide rules.  There are a lot of helpful tutorials these days so I think the material is more approachable by mere mortals.

Hang on to that AD2.  When you get to filters and amplifiers, it will shine.  The network analyzer alone is worth the cost of entry.  Just hook up a low pass filter and try it out.  Sweep the frequencies of interest and you get a Bode' Plot of frequency and phase.  This is as close to magic as it gets!  Pick values that result in a corner frequency around 1 kHz and see what happens.

And we have MATLAB and Simulink!  How easy can it get to model control systems?  Drag and drop!

 


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