To choose an oscilloscope

Discussion in 'General Electronics Chat' started by TBayBoy, May 26, 2011.

  1. TBayBoy

    Thread Starter Member

    May 25, 2011
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    I'm a first year EE student and currently have my home set up of a multi meter and variable power supply.

    I figure the next step is to source out an oscilloscope, and from what my looking around turned up I have a couple of choices.

    Build a pocket unit like this one:
    http://www.sparkfun.com/products/9484

    a PC based one:

    or something on EBay

    My budget is about 200.00 and the intended use is my own lab circuits for school and then transition to hobby radio and clock work.

    I would be interested in your opinions on sources, pre built or kits, features, specs etc.

    thanks.
     
  2. tom66

    Senior Member

    May 9, 2009
    2,613
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    Which currency is the 200 in? USD, GBP, EUR, other...?

    I'd highly recommend looking around for local surplus stores. Used test equipment is often available cheap from them.

    I bought my HP 54501A from a local store for just £150, including one scope probe. 100 MHz bandwidth, quad channel, digitising, with CRT monitor.

    Then again, if you can stretch your budget to $300-350 (assuming USD) you can pick up a *new* Rigol DS1052E. With a simple modification, they can be converted to DS1102E's - 50 MHz vs. 100 MHz. I'm not sure if the newer scopes support it, though; it's a software thing.
     
  3. TBayBoy

    Thread Starter Member

    May 25, 2011
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    Ooppss!!

    Canadian or US currency, it's all the same, just different ink :)
     
  4. Jaguarjoe

    Active Member

    Apr 7, 2010
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    90
    For a PC scope this is pretty good for the money:

    http://www.pdamusician.com/dpscope/index.html

    He's working on a newer, cheaper version that has a logic analyzer and maybe a signal generator. Wolfgang is a good guy, he's on another forum I frequent. He won't steer you wrong.

    That Sparkfun part doesn't get rave reviews.
     
  5. TBayBoy

    Thread Starter Member

    May 25, 2011
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    That DPscope looks really interesting, good like, thx
     
  6. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
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  7. guitarguy12387

    Active Member

    Apr 10, 2008
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    Just picked up a 100MHz Tektronix 2235 on ebay for a hundred bucks (plus 50 shipping for that hefty thing... )

    Cant argue with that though! It should do the trick for me (audio work mostly! Some work with DSPs/micros too.... logic analyzer is next!)
     
  8. CVMichael

    Senior Member

    Aug 3, 2007
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    I got this 34 CHANNEL LA1034 LOGICPORT LOGIC ANALYZER, 200MHz with compression, 500MHz without compression.

    Also, I turned it into an Oscilloscope using an analog to digital converter AD9059 + LTC6904 + PIC16F88 (as main parts). The AD9059 goes up to 60 MSPS.
    The software for the logic analyzer turns digital data into analog representation on the display.
    And if you use the oscilloscope, you still have 24 more channels as digital... so you can measure analog and digital at the same time! I just love this thing.

    I have the schematic in DipTrace and the code for the PIC in mikroC if anyone needs it? (or pics, or movie with it working, let me know)
     
  9. TBayBoy

    Thread Starter Member

    May 25, 2011
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    I've been looking at ebay, cautious though because I have very little experience and i see some of the write ups but not sure of exactly what "keywords" to look for. A picture of a working unit is important but some say calibrated, some don't say. Even if calibrated, how might that change with shipping, change in environmental conditions etc.
     
  10. tom66

    Senior Member

    May 9, 2009
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    Calibration is not crucial, but it is nice. Without calibration, you can't be certain the scope is displaying what the circuit is truly doing e.g. voltages or times may be off. But for general analysis of circuits, it should be okay. Look for scopes which are displaying the 1kHz test signal built into them.
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    I've in the industry and we always maintain equipment with a current calibration,typically once a year. Most items get picked up by a local cal house and tested back in his shop, but the occasional oddball piece gets shipped off who knows where. So calibrating then shipping isn't the worst thing.

    Any decent piece of equipment is going to work indoors anywhere so unless you intend to go outside winter or summer or a rain storm "environment" isn't a factor.

    Get as high a bandwidth as you can afford, 50-100 MHz minimum. While I think that Sparkfun unit is "cute" it can only do 5M samples/sec, which is at best 2.5 MHz.

    I personally have a Tektronics like Guitarguy got. They are very good units.

    One choice is digital or analog, and that will depend if you are doing digital or analog work, mostly because of triggering. Digital scopes are just great at capturing single events (like press a button once and see the circuit respond) whereas analog need a periodic signal to see anything. Digital scopes can get fooled (aliasing) but if I had to choose 1 scope it would be digital.

    I have both types on my bench at work.

    One thing not mentioned is PROBES! Good probes are not cheap. Cheap probes are not good. The BK Precision PR33A at $40 USD a piece is decent, I believe I used these a few years ago and got a year + of hared work before they broke (tip broke off, that's typical).
     
  12. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    Here's my recommendation -- YMMV. I'd stay away from USB scopes and small logic analyzers as your first scope. Get a traditional two channel scope in the 20-100 MHz bandwidth range. You're going to want the knobs and buttons to adjust things. You'll learn this the first time you have to take the scope somewhere away from your bench and have to lug extra stuff with you (like a laptop).

    The first choice to make is analog or digital. I'm still using a 25 MHz analog Phillips scope I bought back in the 70's. It does what it always did. However, as ErnieM said, the digital scopes are better for transient and one-shot stuff (unless you have an old storage scope -- and they weren't all that hot to begin with). I use the feature of pressing a button and saving the waveform or data to a USB flash drive constantly for documentation.

    Use the rule of thumb of dividing the bandwidth by 10 to tell you the upper limit of signal frequencies you can make decent measurements with. Thus, with a 100 MHz scope, you can e.g. deal with 10 MHz square waves. Of course, you can make measurements to higher frequencies if you know your scope. My 25 MHz Phillips scope will trigger to over 60 MHz and I can make measurements on sine waves up to around those frequencies because I characterized it with a function generator.

    Years ago I bought a 4 channel HP digital scope used on ebay, as I had used one at work in the 90's and liked it because you didn't need an instruction manual -- it was trivial to figure out (i.e., well-designed). I still feel of all the scopes I've used that the analog scopes still typically trigger better than the digital scopes do. But I would never buy an analog scope again because of the convenience of digital. And the digital scopes keep getting better and lower in cost.

    Calibration isn't critical but it sure is nice. The digital scopes typically also do all kinds of measurements for you, which saves a lot of time. I use frequency and RMS voltage measurements by far the most. They also have the ability to average the signal, which is very handy for getting rid of random noise. Another feature of digital scopes that I use a lot is the ability to apply a digital filter, such as low pass, high pass, band pass or band reject. This saves you from needing another measurement box or building your own circuit.

    Digital scopes also provide +, -, *, and / arithmetic on signals (* is useful for instantaneous power waveforms; - is useful as the poor man's differential measurement) and FFTs.
     
  13. TBayBoy

    Thread Starter Member

    May 25, 2011
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    Well I took the plunge, bought a BK Precision 2125A with manual, probes, etc.

    Just have to wait for the shipping :)
     
  14. tom66

    Senior Member

    May 9, 2009
    2,613
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    Looks like a good scope, but I think you could have got a better deal second hand.
     
  15. TBayBoy

    Thread Starter Member

    May 25, 2011
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    Hitting my head with my hand... I didn't add it was second hand :) so with shipping $260.00, sorry for my brevity.
     
  16. tom66

    Senior Member

    May 9, 2009
    2,613
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    Ah great! Good to know, doesn't look like a bad scope... delayed sweep looks nice.
     
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