Author Topic: Worth buying a mixed scope?  (Read 3797 times)

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Offline dt

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Worth buying a mixed scope?
« on: January 06, 2012, 12:33:55 am »
Hi all,

Buying my first scope and trying to decide whether choosing an MOS is worth the investment. There seems to be a huge price premium on mixed signal devices, while the logic analyzer features are very poor compared to much cheaper pc-based stand alone logic analyzers (especially in regards to triggering and protocol analysis). My question is the following:

I get the impression that the benefit of a mixed device (as opposed to independent scope and logic analyzer) is the synchronized triggering and display, is that right? How important is that in practice, that is, in what applications or circumstances exactly, would this feature be required?

I'm a software engineer working on robotics and mechatronics projects during my spare time, i.e., it's a hobby thing, I'm not looking to do this professionally - however I will probably buy a scope only once so I don't want to select something inadequate for the future.

Many thanks for your help!
 

Offline IanB

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Re: Worth buying a mixed scope?
« Reply #1 on: January 06, 2012, 09:28:12 pm »
Dave often says that a standalone USB logic analyzer is more useful and flexible than the one built into an MSO. So it's probably worth saving the money on that feature and getting an ordinary DSO.

It's also often said that for some jobs an analog scope can't be bettered, so a well stocked bench should have both analog and digital scopes.

IMHO the aspiration to only buy one scope is unrealistic. Buy what you need now, use it for a while, and upgrade when/if you find the need.
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Offline Lightages

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Re: Worth buying a mixed scope?
« Reply #2 on: January 06, 2012, 09:34:16 pm »
Seeing the analog output or analog triggering event of a digital/analog circuit is mainly the benefit of having a MSO. Unless you intend to make or trouble shoot circuits where it is necessary to see these mixed signals and their interaction in real time, then don't spend the money on a DSO IMHO. I do not have nor have I ever used an MSO so take what I say with a grain of salt. As IvanB has said, get a DSO, and analog scope, and a USB logic analyzer. Much cheaper and more versatile.
 

Offline Short Circuit

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Re: Worth buying a mixed scope?
« Reply #3 on: January 06, 2012, 09:37:29 pm »
If the option comes for cheap, than I would probably go for it, otherwise don't bother.
I have a 'serious' Agilent on my desk for some 6-7 years now, which can be upgraded to MSO, yet I never even remotely considered doing that. And I make a living of these things, so the bucks are no problem if there's a problem that might be solved with such feature. Must add that's it's a 4-channel scope. With a 2-channel, some logic inputs might be more usefull.
 

Offline dt

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Re: Worth buying a mixed scope?
« Reply #4 on: January 06, 2012, 09:42:35 pm »
Seeing the analog output or analog triggering event of a digital/analog circuit is mainly the benefit of having a MSO. Unless you intend to make or trouble shoot circuits where it is necessary to see these mixed signals and their interaction in real time, then don't spend the money on a DSO IMHO.

Ok, but in what applications or circumstances exactly would such a need arise? Examples please?
 

Offline Lightages

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Re: Worth buying a mixed scope?
« Reply #5 on: January 06, 2012, 09:55:35 pm »
An example might be you trying to use a CPU and ADC to monitor an analog waveform. Maybe you are trying to do AC quality measurement and control a number of digital devices depending on the quality of the power. In this case it might be useful to have "perfectly" synchronized displays to show you when the event happens in relation to the digital output.

In many cases it is enough to have a DSO waiting to trigger on the output of the CPU/ADC to see what caused the specific output. If you want to decode the byte and use a specific bye to trigger the scope it is easy and cheap to build byte triggering circuit using simple logic.

There are other cases where MSOs are usfeul otherwise they would not exist but I have never run into the need yet.
 

Offline JuKu

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Re: Worth buying a mixed scope?
« Reply #6 on: January 06, 2012, 10:25:39 pm »
Imo, for a same amount of money, you are much better off by buying a dedicated logic analyzer (such as Zeroplus; the software is awul, but it is still  real good value for money) and buying a faster scope. I have an old Agilent MSO, but over the years i used it, I never needed the dual capacity. Since I got my Zeroplus, I haven't turned on the digital side of the scope, and I don't think I ever again will. You need the bandwidth much more than having the two functions in a same box.
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Offline PeteInTexas

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Re: Worth buying a mixed scope?
« Reply #7 on: January 07, 2012, 04:36:36 am »
If its just a hobby and you can't think of pressing need for it, then it is definitely not worth it.
 

Offline EEVblog

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Re: Worth buying a mixed scope?
« Reply #8 on: January 07, 2012, 09:46:18 am »
Seeing the analog output or analog triggering event of a digital/analog circuit is mainly the benefit of having a MSO. Unless you intend to make or trouble shoot circuits where it is necessary to see these mixed signals and their interaction in real time, then don't spend the money on a DSO IMHO.

Ok, but in what applications or circumstances exactly would such a need arise? Examples please?

I had a very tricky problem once that involved an embedded system mysteriously resetting. I needed 4 analog input to monitor various PSU's and other things, and triggering from the logic channels on certain specific conditions. So I needed to what the analog signals were like before and after the digital condition was meant.
That's exactly what mixed signal scopes are for, if you MUST monitor analog and digital signals at the same time.
You can do it with separate logic analyser and scope with triggering inputs and outputs, but you don't get all the info overlayed on the same screen all time correlated, and that's the advantage of mixed signal scopes.
It's not often that I've truly needed this capability though.

Dave.
 


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