Beginner Oscilloscope for Analog Video Signals - Page 1
Forum section: electronics / beginners

author: CkRtech
author_rank: Regular Contributor
timestamp: June 03, 2014, 10:35:11 pm
content: Hey all -I have never owned an oscilloscope. I am trying to get a good idea of what is "good enough" (to save money) for my first scope purchase based on what I plan on doing with it. I'm absolutely fine with an analog scope - I'll worry about the space for it later.What I plan on doing is using it to try and measure output of analog video signals such as composite, Y/C, RGB, sync, etc for diagnostic purposes. I enjoy modifying old video game consoles for better video output, and would prefer to have a tool that helps reduce the total volume of guesswork when it comes to oddities showing up on the TV - such as interference, etc. Is noise from some other component getting into my video output? Is my +5v noisy and therefore causing visual oddities in my output, etc.I am not an inventor of these mods - I just follow various guides online and use a multimeter as needed. Lately, I have had some odd issues with video output from one project. As for the solution - I am pretty much at the mercy of those on various gaming hardware forums that have the same problem I do. I'd like more "in-house" diagnostic options!I'm open to any thoughts/suggestions you all may have regarding a scope to use or even tutorials with a focus on analog video signals (if those exist).Thanks!

author: 128er
author_rank: Regular Contributor
timestamp: June 03, 2014, 11:08:01 pm
content: Hi CkRtech,maybe this video can help you :This old Hamegs are fairly reliable and with a little bit of luck cheap. And you can get full documentation online. It even has a TV trigger mode. What suits perfect for your requirements.Hope this helps you.

author: N2IXK
author_rank: Frequent Contributor
timestamp: June 03, 2014, 11:18:03 pm
content: Whatever you get, you will definitely want a TV trigger mode, selectable for vertical or horizontal scan rate.If you are looking to make serious measurements on analog video signals, consider an actual video waveform monitor and vectorscope. These are available quite cheaply now that analog video is fading away.

author: pipe
author_rank: Contributor
timestamp: June 03, 2014, 11:42:22 pm
content: Since the bandwidth for the signals you're going to look at won't go much higher than about 15 MHz, pretty much any scope will do for that. Any eventual ringing and power supply noise should also be lower than 15 MHz, but anything above 15 MHz is of course a very nice bonus. Make sure you get at least two channels, and a TV trigger (that's actually very common). I would personally not want anything lower than 40-50 MHz, because even in the C64 you have a 28 MHz clock ticking around, and you'd want to see if such things shows up in the signal.

author: CkRtech
author_rank: Regular Contributor
timestamp: June 04, 2014, 12:58:50 am
content: Wow! I really appreciate this input. Thank you all.

author: CkRtech
author_rank: Regular Contributor
timestamp: June 28, 2014, 12:07:18 am
content: Bumping my own thread here with some follow-up. I would like to open this up to tell you what I am trying to learn/do. I didn't get into specifics in the initial post because I am quite naive, but here it goes...There are quite a few gaming consoles that require components in the cables in order to get RGB output "display ready." There are references out there for what components are needed. Here is one comprehensive one -http://members.optusnet.com.au/eviltim/gamescart/gamescart.htm. I understand it is easy to just follow a guide and buy the appropriate components when creating a cable, but I would much rather get used to looking at a datasheet, learning how to use a scope, and saying "ahh yes. That fits. The value on my scope matches the expected output the datasheet specifies here..." Or perhaps it doesn't match the value, and I need to use different components than a guide on the internet shows.Specific items I might want to do -1: Check output of R, G, B signals to make sure the output is in the correct range. (What if it is 1v p-p when it should be 0.7v?)2: Look at a 15khz composite sync signal and gain a better understanding of what it should look like and what should be done if the signal is too weak or too strong.3: Use a scope to verify that noise from a chroma signal is getting into another signal (happens on Sega Genesis).4: See the difference in quality a cable can make by comparing a signal at the output of a console with that on the other end of the cable.Would a Rigol DS1102E (which is ~$400) as a general purpose scope fit my needs? Is it overkill? It is rather high-priced compared to say $100-$150 analog scopes I see on ebay, however it is new, comes with a warranty, and takes up less space. Ha. But then look at the price and the bandwidth. Do I really need 100 Mhz? Based on what you guys have said in this thread, the answer is no.Do I buy a newer digital scope for peace of mind regarding calibration as well as workbench space (mine is fairly small), or do I stick with the analog scope & just ...put it on the floor with the screen facing up/put it on the bench when needed?

author: miguelvp
author_rank: Super Contributor
timestamp: June 28, 2014, 12:32:26 am
content: I'm currently working in digitizing 240p from a Sega Saturn for now and later for other retro consoles.My "upgraded to 200MHz" DS2072 can handle that, Only 2 channels and sometimes I wished I had the extra 2 channels like the DS1074Z.I'm bloggling my progress in this thread:https://www.eevblog.com/forum/beginners/converting-15khz-analog-rgb-to-digital/msg459236/#msg459236I think intensity grading is important as well as deep memory storage.The DS2072A can be upgraded to 300MHz.Not sure up to what frequency the DS1074Z can be upgraded to, I think it's 100MHz. But even at 70MHz for slow pixel clocks might be just fine:https://pineight.com/mw/index.php?title=Dot_clock_ratesBut when you go to 1920x1200 Vesa, then 200MHz almost can barelly cut it with a pixel clock of 193.16 MHzhttp://tinyvga.com/vga-timing/1920x1200@60HzMy recommendation would be the DS2072A, sure you will have to work at 2 channels at a time but you can use the External trigger for timings as well.Obviously I don't know about other scopes, so something of similar specs might do. Analogs are nice but I like to be able to take screenshots and document my progress.Edit: Even if I have video triggering, it doesn't support 240p but you can easily set it up for a pulse trigger based on the vertical sync.

author: pipe
author_rank: Contributor
timestamp: June 28, 2014, 09:26:07 am
content: Quote from: CkRtech on June 28, 2014, 12:07:18 amThis is a very healthy attitude. The guides are often incorrect, because someone's friend once said that it worked when he put such and such resistors in there, and that circuit made it into an ASCII schematics which in turn was sourced on some wiki, etc. Some guides also use ancient components, and your scope will be excellent when it's time for you to check if the newer stuff works.This subject is somewhat relevant to me atm, I designed an S-Video extension for the Amiga 1200 just a few weeks ago, it shipped from OSH Park yesterday. It's my first OSH Park order, so it'll be interesting to see how it turned out. $8.50 in total for 15 boards, shipped to Sweden.Quote from: CkRtech on June 28, 2014, 12:07:18 amIf you think that spending $400 on a scope is reasonable, then I suggest that you buy a Rigol. No one ever thought "Gee, I wish my scope was slower.". You don'tneedthe extra bandwidth, but it gives you some extra peace of mind. Regarding the size, I already have a 100 MHz digital scope but since it's old and large, I still sometimes consider getting a Rigol so I can take the scope with me.