Which scope?

Discussion in 'General Electronics Chat' started by spinnaker, Nov 15, 2009.

  1. spinnaker

    Thread Starter AAC Fanatic!

    Oct 29, 2009
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    OK I know this question has probably been asked a million times. I did some searching and found nothing that exactly fits my requirements.

    After many, many years, I am getting back into the hobby. My concentration will probably be digital but will probably dabble in the occasional analog (probably mostly repairs).

    I'll be messing with PICs and really want to build a 6502 computer (the first computer I ever used was 6502).

    I'm looking for a scope. I have been checking on ebay and anything above 100MHZ appears to be a bit expensive on eBay (at least I have yet to see any deals). It is not that I am afraid to spend money for good equipment but if things don't pan out for me, I don't want to lay out a bunch of cash for nothing.

    So my question, can I get by with 100MHZ or should I hold out for something better?


    Or since I will be working with digital, should I get a logic analyzer instead? I have one used one once or twice many, many years ago, and I am not sure if I even remember how to use one.

    If I go that route, what should I look for? What features?
     
  2. SgtWookie

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    Jul 17, 2007
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    I bought a couple of used 60MHz 'scopes on an auction site a few years back; a Tektronix and a Hitachi. They work OK for low frequency stuff, but really "run out of steam" by the time I get into the 20MHz range; digital waveforms require lots of bandwidth. If you wonder why that is, it's because square waves are the sum of all of the odd harmonics of a fundamental frequency; and the harmonics go into the GHz region.

    See this Wiki page:
    http://en.wikipedia.org/wiki/Square_wave
    Scroll about halfway down; you'll see an animated GIF on the right which shows what I'm talking about. With even a 100MHz scope, looking at a 20MHz square wave signal looks like the Rocky Mountains.

    100MHz is pretty low-end, but you can get by if you understand what you're not seeing.

    You can "sort of" get by with analyzing repeating blocks of digital data by using the x10 feature of some analog scopes, and adjusting the horizontal position. However, if the data isn't repeating, or the chunks of data are very large, that technique is dicey at best.

    Digital storage scopes are great - until they break, and you have to shell out the $$$ to get them repaired.

    I've seen plans online somewhere for building a simple logic analyzer.
    Google brings up quite a few hits: http://www.google.com/search?hl=en&source=hp&q=Logic+analyzer+schematic

    You first have to define what you really need, vs really want.
     
  3. spinnaker

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    Thanks for the link SW.

    I guess what I am trying to do is to define what I really need. As I said I am a re-newbie at all of this. It has been many years since I have touched any of this and things have changed a lot over the years.

    So the question still stands, if I am going to be working things like PICs and my 6502 project, what do I need that won't break the bank? I'd like to stay under $300 for a scope if possible.


    A logic analyzer project would be really interesting. The more I look into this hobby the more projects I ind that I want to build. :)
     
  4. spinnaker

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    As an added thought. When I was involved, I am not sure I really understood the theory behind what I was doing. Maybe that is what I am trying to do now.
     
  5. BMorse

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    Sep 26, 2009
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    With most PC's running over 2Ghz, and the abundance of USB ports, have you thought about PC based oscilloscopes or logic analyzers?? I use this one from Intronix, works well for some of the stuff I do, (Mostly digital, some analog here and there)....

    http://www.pctestinstruments.com/

    My .02
     
  6. spinnaker

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    But test equipment looks so cool! :)

    Seriously, so the thinking is, that given my interest in digital, I might invest in a logic analyzer first?

    I found this one here

    http://www.saleae.com/home/

    Half the cost of the one you posted BMorse. What do you think?

    The oly problem is that I will need to upgrade my "lab" PC. :) Maybe I can make do with my main PC for a while. It is right nearby. :)
     
  7. BMorse

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    Sep 26, 2009
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    I am not familiar with that one, but it seems as if it doesn't have all the capabilities and speed as the Intronix one.... but could be a good start for what you need it for.... I am sure other people know of different ones also...
     
  8. spinnaker

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    But is my statement correct in that I really should be looking for something like this instead of an oscope?

    I would be interested in other suggestions for a logic analyzer.
     
  9. ftsolutions

    Active Member

    Nov 21, 2009
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    +1 for the Intronix LogicPort - it is a great little device and does the job (with suitable PC of course) of logic analyzers that one would have had to shell out $30,000 a couple years ago. Mine travels with me all the time in my laptop PC bag (I'm an embedded systems consultant) and I often carry a Tektronix 2024 digital scope in my other bag. Together they handle at least 80% of all the debugging I have to do in my business.

    I realize that you are on a budget, and it is for hobby, not business use. But, one does generally get what one pays for with oscilloscopes. I've used Tek scopes for over 3 decades now (along with other mfgrs), and I keep coming back to them.
     
  10. slick41st

    New Member

    Nov 21, 2009
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    Hi Guys, I have worked on and sold most major brand scopes for 20+ years.
    ftsolutionms is right that Tek are a good brand, but may be out of your price range spinnaker.

    I am not selling test and measurement equipment anymore, but if I were buying a brand right now it would be Rigol for a bench scope, and Pico Technology for a PC based scope.

    The Rigols simply have great functionality, are lower cost, and are excellent quality.

    Spinnaker, in order for me to give you any guidance, what is the fastest clock speed you will look at? The higfher it is, the higher the BW needed on the scope, and if you need high BW and a deep memory, then that will be expensive. Typically the better (read smarter) the triggering system, and the
    more you know what type of signals you will be looking for, the easier it is to fit you into a lower memory scope.

    For PC based LA's, have a look at the Acute series, these are reasonably priced for their performance.

    Cheers!
     
  11. spinnaker

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    Thanks for the help. I already purchased a 200 MHZ 2 channel Tek ocsope from ebay.

    Given that, what is the fastest clock speed I can easily measure? :)


    My first few small projects will probably be with encoders, decoders, PICs etc. Then I plan on moving to building my "single" board 6502 computer. I want to do it old school with 7 segment display and hex keypad. I plan on running it on a 2mhz clock. Since I am having a hard time dinding a hex decoder for the display, I might even add a bit of new school and add a PIC to handle all of the user UI.
     
  12. SgtWookie

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    You should be able to go up to around 50MHz digital without too many problems, if you have decent 1x/10x/100x scope probes. Higher than that, you'll have to know what you are looking at in order to be able to interpret it properly.

    With analog signals, you'll be able to see sinewave signals up to nearly the 'scopes rated bandwidth. With square waves, you're back to 50MHz or so.
     
  13. spinnaker

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    Tks Sgt,

    I don't see me going much beyond 50 MHZ for digital any time in the near future for my digital projects. I would imagine speeds like that carry their own design challenges that would be better off avoided by the beginner.

    I ordered a cheapie pair of 100mhz 1x probes just to get me started. I figure I could always upgrade later.

    When it comes time to upgrade (and maybe I should ask then but...), what should I look for? What would I expect to pay?

    I used to know the purpose of the 10x, 100x probe. Can you refresh my memory?

    I guess it is going to take a while for me to remember everything I learned about scopes. :)

    I can remember doing some pretty fancy things. I remember having this one scope in for a few weeks. I seem to remember it had some fancy time delay features. We had a load of boards not functioning. These boards had been laying around for a couple of years and no one could fix them.

    I knew it was some kind of time delay problem on one of the chips. I made sure I learned how to use our new fancy toy. It would not be around for long because it was expensive to rent. I was able to prove my timing problem and narrowed it down to the specific chip. I grabbed several of the same chip from the supply room and still had the same problem with the boards. I reasoned that it could be the circuit around the chip, so I built a little test circuit for the chip. Same problem. I then thought maybe a bad batch? I went to Radio Shack and purchased a few chips. Popped one into my test circuit and it worked perfectly. Popped one into one of the bad boards and the board worked perfectly. We had couple hundred chips, with the same batch number. I had to assume they were all bad.

    I went to our buyer and asked him to order a bunch of chips. I told him. DO NOT ORDER FROM THIS BATCH NUMBER. In fact see if you can get them from a different manufacturer. BUT DO NOT ORDER FROM THIS BATCH NUMBER. A few weeks goes by, the buyer sees me and says, how many of those chips did you want. I told him again and repeated DO NOT ORDER FROM THAT BATCH NUMBER!.

    A few weeks go buy. I get my chips. I am very excited. I open them up and look at the batch number. Guess what? :) OK Tested them anyway in my test circuit. Same problem. I went down to Radio Shack and cleaned out their inventory. :)
     
  14. spinnaker

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    I remember now 10x = higher impedance! :)
     
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