Are Software Oscilloscopes a Good Alternative?

Discussion in 'General Electronics Chat' started by BadBadger, Apr 5, 2014.

  1. BadBadger

    Thread Starter New Member

    Feb 1, 2014
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    Can anyone offer advice, or point me to a thread, regarding software-based oscilloscopes? I've seen a couple of these things, but it's hard to tell if they really are a good alternative to hardware. It seems like they are less expensive and buying an inexpensive laptop could also be useful for programming Arduinos, etc.

    Thanks!
     
  2. w2aew

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    Jan 3, 2012
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    It's really personal preference. But for me, I'm not a fan of them. If I'm poking around on a circuit with a scope probe, I want to be able to reach up and turn a knob to adjust the scope - not find a mouse, click a field, and type on the keyboard. Not to mention the potential noise issues, ground issues, etc.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    The typical software oscilloscope uses - and is thus limited by - the audio input hardware of your computer. Since that probably tops out at 20kHz or less, even a 5kHz sine wave will show a lot of chunkiness. Similarly, on the low end, a DC signal will be decoupled (which is a good thing). If you're watching frequencies between, say, 5Hz to 2kHz, a software oscilloscope can do a fine job. Very handy and very cheap (assuming you have a computer).

    Be very careful when you connect your probe "ground" to another ground, though. Current can flow with only the ground connection, and this current can ruin your sound card. You have to check for voltage before making connections. A laptop floats when it's not connected to its adapter, so it's not an issue with an isolated supply.
     
  4. BadBadger

    Thread Starter New Member

    Feb 1, 2014
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    It sounds like that route could be useful for audio frequency purposes like testing and calibrating synthesizers, which would be a primary use for me, but that for higher frequency digital use it would be lacking.

    Now that you've given me a little advice, I'm going to dig a bit more. But I imagine hardware scopes are still firmly on my radar.

    FWIW, one I saw was a USB scope. Wouldn't that be potentially better than an audio interfaced scope? Or do they have their own issues?

    Thank you.
     
  5. strantor

    AAC Fanatic!

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    I've been researching USB scopes myself (USB MSOs octually).. My opinion after looking at just about everything out there, is that you can get a really awesome USB scope for about $1500 and up. Everything that costs less than that is crippled. If your budget is <$1000 and portability isn't a concern, you'd be better off to buy a nice used bench scope.

    For me, since portability is my #1 concern, I'm waiting for technology to improve and prices to come down.
     
  6. Little Ghostman

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    Jan 1, 2014
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    I just dont like the idea of plugging something like that into my laptop! If your going to spend >$1000 on a scope then unless you need portability it would seem silly not to get a decent secondhand bench scope.
    I have 2 favorite scopes that I use most, one is a very old gould 250MHz, it does all kinds of maths on the waveform and must have been light years ahead in its day, it even has a working printer in the top of it and 4 channels. It cost me £100 on ebay

    My other favorite is a old Lecroy 450MHz 4 channel, it dosnt have as many maths functions as the gould, but its a lovely scope to work with and cost me about £300 (thats huge money for me).
    My favorite analogue scope is a tectronix (I forget the model) I dont use it much but again 4 channels and really nice, it is the most expensive scope I have ever brought at around £360!!! I dont use it much because it needs calibrating, the two DSO scopes I use are still bang on and dont need adjustment.
    Its a taste thing but I wouldnt swap a bench scope for a pc based one for anything, to me they just dont look right!
    Also both the gould and Lecroy can be connected to the pc anyway, I also got hold of a PCI GPIB card for the pc, I waited and waited and eventualy won one on ebay for £35!! score!!!
    I still grumble at the GPIB cable cost though.
     
  7. GRNDPNDR

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    Mar 1, 2012
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    Tektronix digital scopes are pretty portable, in terms of being fairly small, light, and easy to move/carry.

    I only paid $432 for mine on ebay, but it is only a 60Mhz model.
     
  8. Mike33

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    Feb 4, 2005
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    Not to rain on anyone's parade at all, I got a 60MHz Tektronix ANALOG scope for $90, including shipping. But it's from 1982 and big and heavy! And doesn't have cursors and all the fun things yours has, GRNDPNDR!

    How much you spend on a scope, and what you end up with, really depends what one wants to do, I think! I build amplifiers, make guitar effects etc. Don't need anything more than an old CRT scope. In fact, it may work BETTER than many digital ones, for what I'm doing. But the digital guys might need to see MUCH faster switching that I can't...doing a fair bit of homework before buying big test equipment is always a good thing to do!
     
  9. GRNDPNDR

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    I'm somewhere in the middle here, I play with amps from time to time, but I'm also 'educated' in digital and should I need to do some digital work this scope may be better.

    Basically it's the exact model we used in school so I'm familiar with it and I know it will work for most of the stuff I do since I rarely do much beyond what we did in school.

    EDIT**
    I should also mention, I got mine so cheap because it came with absolutely nothing. no probes, no books, no software, no power cord.

    I already have probes and power cords so that wasn't an issue....but I do wish I had the software and manuals.
     
  10. Little Ghostman

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    The one thing I like most about my analogue scope is, it has the cursors etc that my digital scopes have. If I had to choose only one scope to keep it would be probably be the Gould!! Although the Lecroy is very close behind.
    In the end no scope is any good if you dont get to know it and how to use it. For a long long time I fumbled around then slowly after watching scopes for dopes etc I started to learn how it works. All the bells and whistles mean nothing if you cant even set a simple trigger up. As one or two post's on this forum prove, a scope is only as good as the dope using it lol :D.
    Well done Alan I love that video
     
  11. MaxHeadRoom

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    I own both, for general portable work and work out in the field I picked up one of these, http://www.syscompdesign.com/
    When they first came out, I picked up a promotional ver for $100.00.
    My old Tektronix is just too heavy to lug around.
    Plugs into the USB port and the advantage is the storage feature where you can keep something on record for future comparison.
    Not high freq, but if you just need low demand run of the mill projects, it works.
    Max.
     
  12. BadBadger

    Thread Starter New Member

    Feb 1, 2014
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    Thanks, everyone, for the advice!
     
  13. strantor

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    Oct 3, 2010
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    I'd like to revise my input. When I said I was waiting for tech to improve, I had my head up my ass. Actually, I've had my head up my ass for weeks researching these USB scopes. I just had a big "DUH!" Moment, let me explain:

    I've been comparing USB scopes to bench scopes and been unimpressed with their sample rates. 200Msa/S is cutting edge fast for a USB scope. 200Msa/S on a bench scope has been around for decades. I never stopped to ponder why; just figured that usb scopes were made by cheezy small operations that didn't have the tech that tekronix or agilent has. No. Usb scopes cannot, ever, be as fast as bench scopes because the link between scope and screen is very weak link.

    Your average usb scope has a resolution of 8 bits, AKA 1 byte. At 200Msa/s, thats 200Mbytes per second. My laptop only transfers to 7200rpm hdd at 125Mbytes/sec. So already, with a single channel of this weak ass (compared to bench scope) usb scope, im already spitting out more data than my computer can accept. Usb 3.0 has a max transfer speed of 5Gbits/sec, so theoretucally the fastest a usb scope could transfer to a pc (given the pc can accept it) for a single channel is 625Msa/s. 2 channels, cut that in half. 4, in fourths.

    But forget about usb and the hdd. I've got 10Gbit/s ethernet, lets use that. Some pc based scope use ethernet, so why not? And since my hdd is so slow, we'll send all the data to ram. Now I can have the 1Gsa/s pc scope I've always wanted! So I hook it up and sample 2 channels, and consume my entire 8GB of ram in half a second and crash my computer. (Assuming whatever bus between ethernet port and ram supports 10Gbit/s transfer).

    So when I look at these entry level bench scopes with > 1Gsa/s for <$600 and wish that I could have that in a usb scope with 4 channels and a sample rate rivaling the fluke scopemeter at 2.5Gsa/s, I'm being a real igoramus.

    Reality check! Pc based scopes are never going to get anywhere near bench scopes in performance. The fact that the bench scopes can take such measurements and store all that data so quickly explains why they are so damned expensive; another thi g that was a mystery to me until just now.
     
    Last edited: Apr 7, 2014
  14. MrChips

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    I think you are confusing two different rates, sampling rate and data transfer rate.
    There is no reason why the PC data transfer has to keep up with the sampling rate.

    You can create a USB scope that digitizes at 1Gsps or 2Gsps. Of course the cost goes up with speed. With 1GB memory and higher being readily available and inexpensive, the USB scope can store 1 second and more of multiple channels.

    The data transfer rate to the PC is mainly for display purposes. Refresh rates of 25 times every second is good enough for our slow human eyes. USB can easily accommodate this.
     
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  15. strantor

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    Thanks for clearing that up mr Chips, I guess it's a case of double rectocranial insertion.

    So, let's say I have a 1Gsa/s usb scope with pre-trigger capture and I trigger on a glitch. Now I want to go back in time and see what happened before the glitch. Does the scope transfer its 1Gb of buffer to my pc in order for me to be able to navigate back in time, or am I sifting through the contents of the scope's buffer when I do that?
     
  16. MrChips

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    It can be either, depending on how it was implemented.
     
  17. MaxHeadRoom

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    The one I linked to has the strip chart recorder function, pre or post trigger.
    Max.
     
    Last edited: Apr 7, 2014
  18. CVMichael

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    I got the MSO-9201, and I am happy with it. I mostly work with microcontrollers, so the logic analizer part of it comes in really handy. The best part is when you work with analog and digital at the same time, you can set triggers on either one (digital or analog), and you can check the state of both on the same timescale... The software for the MSO-9201 needs some improvements, but over all I am very satisfied with it...

    I also have a 34 channel LA1034 Logic analyzer, and it is awesome, and I love the software too. But when I needed to measure both analog & digital at the same time it started to get frustrating. Since it has 34 channels, I used an 8 bit ADC chip see this to turn the logic analyzer into an MSO, but the LA1034 has very little memory for this. That's why I got the MSO-9201, to be able to measure both at the same time.

    I understand that you can't do some things that analog oscilloscopes can do, but it's the other way around too... it all depends on your needs and preferences...
     
  19. wayneh

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    IMHO, the only reason to horse around with a software oscilloscope is that you can get something for next to nothing, assuming you have the PC to begin with. If I had to spend even $100, I'd go looking for an old "real" oscilloscope instead. But for a hobbyist DIYer watching the waveform from a slow 555 oscillator, for instance, repurposing an old PC is a nice solution.
     
  20. strantor

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    Or, 90% of your oscilloscope use is in the field and you don't want to lug around a boat anchor. Something that would fit in my backpack with the laptop that I already carry would be ideal.
     
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