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oscilloscope

Discussion in 'Electronic Basics' started by [email protected], Jun 18, 2007.

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  1. Guest

    I'm a newbie wanting to muck about with picaxe projects partly to
    learn and partly to make some long-wished-for gadgets, eg datalogging
    battery charging and meteorological/power generation info, and a
    keyless front door lock.

    I'm confused about the pros and cons of these two CRO alterrnatives.
    The first seems to be a cheap analogue machine.
    Costs new about $US 350

    The second, a USB computer-based "black box" that doesn't seem to want
    to tell me what the bandwidth is. Maybe it's in there somewhere, but I
    don't know enough to tell. This is around $US 250

    I'd appreciate any advice regarding the usefulness of these in general
    electronics, picaxe, and education for me.
    Cheers, jack

    ###########################

    20Mhz Dual Channel Cathode Ray Oscilloscope

    SPECIFICATIONS

    Vertical Deflection
    Sens.: 5mV - 5V/div (10 steps 1-2-5 seq.)
    Bandwidth: DC to 20MHz
    Rise time: 17.5ns
    Input impedance: 1MO with 25pF shunt
    Max input voltage: 300V (DC and AC p-p)
    Input coupling: AC, GND, DC
    Modes: CH1, CH2, ADD, DUAL
    CH1 output: Min 20mV DC
    Horizontal Deflection
    Sensitivity: 0.5sec/div, (20 steps 1-2-5 seq.)
    Accuracy: ±3%
    Trigger
    Modes: Auto, Norm, TV-V, TV-H
    Source: CH1, CH2, LINE, EXT
    Slope: Positive or negative
    Ext. input impedance: 1M with 25pF shunt
    Probe Adjustment
    Frequency: 1kHz (20%)
    Level: 2V (±2%) p-p
    Duty ratio: <48:52

    X-Y
    X Axis bandwidth: DC to 500kHz
    X-Y Phase diff.: 3° or less (DC to 50kHz)

    Z Axis
    Input impedance: 47kO
    Input signal: +5V (positive INPUT)
    Max. i/p voltage: 30V
    Bandwidth: DC-2MHz
    Power
    Power supply: 220VAC
    General
    Dimensions: 310(W) x 150(D) x 455(H) mm
    Weight: ˜8kg

    CRT
    6° tube: Rectangular face (8 x 10div)


    Features

    • 2 channels
    • Variable sweep
    • 10x magnification
    • 4 trigger modes, auto, norm, TV-V & TV-H
    • Wide bandwidth and high sensitivity
    • Easy to read 6” display
    • Bail-arm stand for ease of viewing
    • Carry handle
    • Very low power consumption
    • High sensitivity X-Y mode
    • Z axis (intensity modulation)
    • TV video sync
    • Filter
    • High frequency rejection filter in the triggering circuit
    • Supplied with 2 high quality test probes

    ##########################


    2 Channel USB Oscilloscope


    At last! A genuinely affordable computer connect oscilloscope. USB
    connect oscilloscopes out of Europe and North America have so far been
    out of the price range for hobbyists, schools, and even many
    professional people. Fortunately, we have been able to work with a
    EUROPEAN manufacturer to produce this compact unit which is packed
    with features and the European quality we've come to know.



    Using the Plug 'n Play USB technology and providing full optical
    isolation from the computer, this oscilloscope is easy to setup and
    use, as well as providing protection for the computer. The software
    (again developed in Europe) is a fully featured chart recorder,
    function generator, logic generator, logic analyser, and spectrum
    analyser all in one easy to use package.



    We think you'll be suitably impressed by this product's price and
    feature list.



    Specifications
    Oscilloscope, spectrum analyzer
    Sample rate: 100 Hz - 200 kHz
    Input voltage -20 - +20 V
    ADC capacity: 10 bits
    Window functions: Hamming, Hanning, Blackman, Blackman-Harris



    Recorder:
    Sample rate: 0.01 Hz - 200 KHz
    Maximum record time: 24 hours
    Input voltage -20 - +20 V
    ADC capacity: 10 bit



    Logic analyzer:
    Number of channels 16 (8 if logical generator is on)
    Sample rate 1 KHz - 8 MHz
    Input voltage: 0 - 5V



    Logical generator:
    Number of channels: 8
    Sample rate: 1 KHz - 1 MHz
    Memory depth: 1544 bit/channel
    Output voltage: "0" - 0 V, "1" - 3.3 V
    Maximum input/output current: 10 mA



    Minimum system requirements:
    Windows 2000 or XP
    Pentium 600MHz, 256MB RAM.
     
  2. Guest

    Thanks for the offer, John, I'm in Australia.
    I was not contemplating actually buying either of these at the moment,
    just doing some ground research about two affordable options at my
    local shoppe. jack
     
  3. I have a few scopes I have bought, used from eBay and
    refurbished, including new electrolytic caps in the power
    supplies. I have an analog storage scope and a non storage
    Tektronix with roughly these specs that I am willing to sell
    for a lot less than $350, each. If you are in the U.S.,
    and want more details, email me with an actual address, and
    we can talk.
     
  4. This sounds like a very ordinary, low end, 2 channel analog
    scope. It would have lots of uses for audio and other
    analog signals, and also digital, except for the timing
    details of digital edges. Even a small, slow microprocessor
    would might react to things you would miss or see distorted
    with only 20 MHz bandwidth. But still potentially very useful.

    The only feature missing that you might find a need for, is
    delayed sweep. when you are looking at digital sequences,
    you sometimes need to examine a detail that is significantly
    delayed from a trigger event. If you use a horizontal sweep
    time long enough to get both the trigger event and the one
    you want to see on the screen at the same time, the details
    are too crowded together to make out anything useful.
    Delayed sweep is 2 sweep generators. the first starts at
    the trigger event, and acts as a programmable delay, that
    triggers the second, which sweeps the trace. In effect, you
    get a programmable delay between the trigger event and the
    expanded trace of some period of time after it. But you
    can, also alternately, see the whole time period, but with
    the delay portion dimmed, and the delayed part brightened,
    so you can set the delay.
    I would say that these specs indicate an absolute bandwidth
    of less than 100 kHz, which is poor for any use except low
    frequency analog and audio stuff. Microprocessors can have
    a lot happen in 5 microseconds (the time between samples).
    This seems to be referring to 1 bit resolution (recording if
    a signal is either above or below a threshold voltage,
    somewhere between 0 and 5 volts. A logic state recorder,
    not really an oscilloscope. But at least it is fast enough
    to follow more of the range of microprocessor signals. This
    sort of thing is normally called a logic analyzer, used to
    capture the parallel processes of buses or other multi bit
    processes.
    Very handy as a signal source simulating the missing parts
    of a system, when you are testing a part of a logic system
     
  5. john jardine

    john jardine Guest

    [...]
    You really need something like 40Mhz-50Mhz. Nothing worse than paying full
    whack for kit and then weeks later find you're hankering for more spec'.
    Myself, I'd buy second hand on ebay.
    Sounds like the work of a marketing specialist. Reads as marvellous but is
    basically useless. It's a data logger at 200kHz samples a second.
    As I'm feeling grumpy, I'll take the cynical path ...
    You need about 600 dots across a display to give a reasonably clear pic'
    (any display). So if you want on screen a single cycle of the waveform
    you're interested in, then it will need to be composed of 600 dots or
    samples. This tells you that the best the device can do is 200,000 samples
    per second / 600 samples on screen = 333
    Hence the frequency response tops out at a heady 330Hz.
    Unit could be useful for monitoring clean mains waveforms or battery
    discharge curves.
     
  6. Guest

    Thanks muchly for that explanation, John,
    it has helped me a lot. jack
     
  7. Guest

    Thanks John.
    That second one is much as I suspected, but wasn't sure.
    I am suspicious when folk "namedrop".
    A clear jargonfree explanation shows they have nothing to hide.
    I think the second-hand route is the way to go. I just need a bit more
    study and research to know what to look for and to know when I have
    found it :)
    So far, I seem to have gleaned that a 60MHz analogue machine is going
    to give me the best bang for the buck. Digital, storage and other
    fancy bits are pretty much jam on the bread.
    Cheers, jack
     
  8. Ben Jackson

    Ben Jackson Guest

    A scope of any kind is going to show you things you just couldn't see
    any other way. Any "real" scope (not a USB logic analyzer) is going to
    let you see moving, repetitive signals that would otherwise be very
    hard to id. It's a quantum leap from a voltmeter for certain problems.
    Storage (which usually comes along with digital) is going to let you look
    at one-shot signals, logic bus transactions, long term averages, automatic
    measurements and more. It's a quantum leap from an analog scope[*] for
    certain problems. However, the prices are commensurate.

    [*] And there are some things an analog scope is better for, too,
    but if I were trapped on a desert island doing mixed-signal design,
    I'd want the digital storage scope!
     
  9. Guest

    Thanks Ben, some more good stuff to think about.
    I've never actually used a scope to do anything real. Way back a few
    class experiments with lissajoux figures and the like, and I've
    watched the techie at work a few times.
    I've got a lot to learn before I lay out the readies.
    Cheers, jack
     
  10. Hi Jack
    Definitely get yourself an analog oscilloscope. New ones are poor
    value, you can get a refurbished unit on eBay or test equipment
    suppliers for much less.

    20MHz dual channel is basic entry level oscilloscope. Although if you
    are looking at 2nd hand refurbished units then 50MHz or 100MHz would
    be more useful.

    Once you have a proper analog oscilloscope *then* think about getting
    a digital PC based oscilloscope. Regards of what PC oscilloscope
    makers claim, they are not a replacement for a good analog
    oscilloscope.

    In todays digital world you really need both, esp if you are into data
    logging type stuff, digital etc. Digital scopes let you capture single
    shot events that analog oscilloscopes can't. And analog scopes give
    you the real-time feedback and resolution that digital scopes can't
    give you (unless you pay >$$$$).

    Digital scopes are tricky when it comes to "bandwidth". They will have
    a "sample rate" which has nothing to do with the analog "bandwidth". A
    *good* digital scope will operate in "real-time" and have a sample
    rate that is at least 10 times greater than the analog bandwidth. e.g.
    1GS/s for 100MHz analog bandwidth.

    Dave.
     
  11. Bob Masta

    Bob Masta Guest

    Not to react too grumpily to your grumpiness <g>, but your
    scenario seems overly conservative and arbitrary. I think
    very few people would agree that 600 samples are required to
    adequately view one cycle of a sine wave... 20 is probably
    more like it.

    If the OP is interested, he can download my Daqarta
    software and use it to look at the output of the built-in
    signal generator. Judge the display quality as you
    raise the generator frequency. The trace area is
    512 samples wide (unexpanded) and the sample
    rate (set by the X-axis dialog) is typically 44100 or
    48000 samples per second, so you can figure out
    the relative pixel resolution of other digital scopes.

    However, one of the big advantages of
    a digital scope is the ease of getting a spectrum
    display, which is often much more useful than a
    waveform display at audio frequencies. You
    probably won't find a spectrum display on any
    entry-level hardware scope.

    Note that although you can use Daqarta as a
    digital scope/spectrum analyzer for audio
    frequencies, I am not suggesting that it is
    in any way a replacement for a fast hardware
    scope. (I have a 100 MHz scope on my bench
    as well.)

    One other advantage of a digital system is
    that the signal generator can be precisely and
    repeatably controlled, and typically can be synced
    to the input process to allow synchronous signal
    averaging. For a stimulus-response type test,
    that allows you to recover responses that were
    totally buried in noise, with no waveform distortion
    or rounding such as would be caused by a filter.

    By the way, the Daqarta signal generator is
    yours to keep, absolutely FREE, just for trying
    Daqarta. Not available in any store! <g>

    Best regards,








    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
  12. If you are in Sydney then I have an old 30MHz analog scope I'm looking
    to get rid of pretty cheaply...

    Dave.
     
  13. That is basically a data logger and not an oscilloscope. The 200KHz
    sample rate makes it only good for audio use up to 20KHz (giving you
    10 samples per cycle at that frequency, a rule of thumb). Seems like
    it only has a single input range as well, that is also very poor.

    It's just a toy, don't waste your money.

    Dave.
     
  14. Guest

    Thanks for the offer Dave, but I'm way over in the Golden West, and
    not yet in a position to invest in a CRO. Just trying to learn about
    them at the moment. jack
     
  15. Guest

    Thanks for that, Bob. Most interesting. I will give that a go, Cheers,
    jack
     
  16. Bob Masta

    Bob Masta Guest

    Note that when you install Daqarta you are *supposed* to get
    30 sessions/30 days free trial of everything, after which only
    the inputs stop working. You are welcome to use it like this
    as a fancy signal generator or WAV file analyzer, etc, for as long
    as you like. However, some people report that they get a
    "NO trials remaining" message on the initial install. If you
    don't want to test the input functions, you can just use the
    signal generator as-is. But if you contact me (use the Contact Us
    form on the site) I will be glad to create a custom trial key
    for you that will give you the original 30/30 trial. (The trial
    problem will be fixed in the next version, in about a month.)

    Best regards,




    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
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