Best $350 scope

[MoltenVoltage]

Digital oscilloscopes keep getting more affordable.

I have narrowed it down to these two but am really torn as to which to buy.

First, the QuantAsylum QA100 is a pure USB scope with very impressive specs for the price and lets you use your screen for a high res interface:
http://www.quantasylum.com/content/Products/QA100.aspx
But it leaves you tied to your computer, and I am usually working on a schematic and/or code when looking at a scope.

Second is the Atten ADS1102C (available for $350 on ebay):
http://www.sparkfun.com/products/10806
The knobs and buttons + portability are very tempting, but the screen resolution is pretty low and from the reviews it sounds like there may be issues with the drivers for Windows 7 in case I want to use it as an interface.

Anyone have experience with either scope or opinions?

[Seljer]

I've seen a lot of people have gotten the 50Mhz Rigol digital storage scope which is in that price range

In any case, my vote goes to a proper standalone oscilloscope

[Earthscum]

Honestly, the QuantAsylum has a total geek factor to it and that's the one I'd go with if I could. Firstly, since you use your own screen, you have a MUCH better visual. Second, they're both digital... I am starting to not like analog display (tube display) because it doesn't save anything. It blips, it's gone... you can't pause and scroll back and specifically measure and study a glitch you notice, or what-not. I really think the QA will give a tone more flexibility than the ADS after all is said and done. Just having your own choice of screen makes a big difference, IME. I'm definitely not well versed in O-Scopes, but in considering the 2 that I own, my vote goes to the QuantAsylum.

[R.G.]

My vote goes to the QA. I've used the Picoscopes on either side of the QA in their comparison for some years now.

I find that the step from non-PC-attached scope to PC-attached scope is nearly as big as the step from no scope to scope. That's based on using scopes since 1972 on a regular basis, including some of the highest-end analog storage and sampling scopes.   

Once you get to PC-attached scope, the more-is-better rule kicks in, as does the law of diminishing returns. I have occasionally been irritated at only 8 bits of resolution on the display, but not enough to lay out another several hundred dollars. As for sampling depth, minimum scales, speed, etc, it's "faster horses, older whiskey..." which you'll understand if you're a C&W fan. The marginal stuff like this always creeps up.

For audio, you really don't need much over a few MHz; even for criminally insane audio. For high speed logic viewed as analog, you can't get fast enough.

As far as logic analyzer action, if you need to design high speed random logic or gate arrays, PGAs, etc., it's probably useful. Maybe for real-time control of motors and such with uCs. I find that mostly I can use uCs to test and develop themselves by writing test cases first, then writing t he application to fit the test cases instead of the reverse. There are occasions for designing high speed logic in audio, but it's way outside the scope (... oops, sorry~!  ) of this forum.

[Earthscum]

I gotta make an argument for "If you can find one..." higher speed scopes for audio. You know that hiss sound that won't go away with filtering? I decided to see if I could track it down, and I did. I tried it with my 2MHz digi hobby scope, and it showed nothing. It was a gunked up connection on my breadboard, and something with the circuit I had in there made it hiss. I had a Mu project on the other half of the board that I tracked the hissing (or, just extra noise) down as well to how I had my wires crossed back over the first gain stage. The signal was only a couple mV at most, but was really high spectrum. All the stuff that PRR and R.G. have mentioned about that, I gotta apply... I was happy with myself!

But, other than that, I've never had any real use, as R.G. mentioned, for the finer divisions on my scope.

[aballen]

I'm curious what you guys think of these two, I've considered them myself.

http://www.seeedstudio.com/depot/dso-nano-v2-p-681.html?cPath=174

http://www.seeedstudio.com/depot/dso-quad-aluminium-alloy-silver-p-1033.html?cPath=174

and no I'm not affiliated with seed studios in any way.

[Fender3D]

Look for OWON 100MHz on eBay
I know it's ~440$ but it has 800x600 screen res and VGA output, thus you can connect any PC screen.
It also has an Ethernet connection and can be shared on a LAN...

[Gurner]

If you're mainly working with audio.....things like the ability to do a bode plot is *very* useful ....which is why I went with a velleman PCSGU250 USB scope

[R.G.]

Something I'd really like to see is a scope similar to the Pico or QA that
- has its own floating power supply, separated from the AC line by a 4000V hi-pot isolation; this is a standard for UL/CE/CSA/TUV/YADA/YADA power supplies, so that's not too big a stretch to do

and

- opto isolated USB line to the PC, so it does not share the PC's ground. The PC's USB could carry power to the scope side of the USB receiver for driving the line, but the scope needs to be floated from the PC's ground

and

- immunity to voltages over 20V; the QA may be different, but the Picoscope line has a 20V max on the inputs. This makes them useless for tube amp work. I've had to twice build external dividers and protection circuitry to use this. It works, but it's a pain.

The ability to capture waveforms, do virtual metering, run spectral analysis, save test setups, etc. is huge once you get beyond simple see-the-waveform scope use.

[MoltenVoltage]

Look for OWON 100MHz on eBay
I know it's ~440$ but it has 800x600 screen res and VGA output, thus you can connect any PC screen.
It also has an Ethernet connection and can be shared on a LAN...

Thanks for all the responses!

The seed ones seem a little small for my purposes.

The Vellman looks cool too, but I sometimes program 40MHz chips so need at least that speed.

I dug a little deeper and was pretty set on the QA100, but the OWON is very tempting as it is battery powered, portable, has a much nicer display, and has 10x the sampling rate of the QA100...but it is only 8-bit instead of 10.  It's also $100 more.

The QA100 is designed for debugging chips which is why I need a digitial scope, as my analog scope makes those jobs more than a little challenging, although it works great for audio and LFOs - assuming you don't mind waiting for the beam to cycle when its on a 1 second sweep 

I love analog audio, but there's no place for nostalgia in test equipment!

While I was typing, RG posted.  Now I am wondering whether the battery power of the OWON solves the isolation issues he describes.   Of course the lithium battery is an extra $75 so now I'm at $525

The OWON also allows 400v input.  The QA says it has 40v inputs, and 200v at 10x probes which doesn't make sense, shouldn't it be 400v?

Here's a link to the OWON manual:
http://www.aidetek.com/New_products_info/Datasheet/owon/SDS7102_manual.pdf

QA100 or OWON?  Or is there an even better scope that the OWON for $500?

[frank_p]

Some standalone digital scopes operate on lithium battery (floating) and have wireless ethernet, FFT algorythms and quite a lot of memory.  400V input.
That is already a lot for very low money.

[Gurner]

I do agree about the PC ground....it's a total sewer, which is really frustrating when you want to work with low level stuff on a USB scope (and when a couple more bits of resoluton would really help!).

[MoltenVoltage]

I was actually logged into ebay about to buy the OWON and thought about what a pain keeping batteries charged is and where I would get a replacement when it dies.

The I realized it can't be that tough to make a USB interface that is battery powered for the QA100.

Just take 2 USB jacks, cut the power connection from the computer and connect batteries to the power contacts for the jack that connects to the device.  The QA100 draws 500 mA at 5 volts, so not a big deal.

Anyone see any issues with this idea?  Any problem with breaking the ground connection?  From what I can tell, the data lines operate independently of the power.

http://en.wikipedia.org/wiki/Usb

Worst case, you could make a battery powered repeater, but hopefully that isn't necessary.

[scratch]

would using a laptop instead (running on it's battery, not connected with an AC adapter) get around the grounding issue?

[R.G.]

Battery powered USB port - not a problem.

Isolating scope-input ground from PC ground - ACK!

Laptop instead - hmmm. Probably OK. I use an older laptop with a battery pack that's dead/dying and a floating laptop power supply for my scope work. I get the 4kV isolation in the floating laptop power supply. The only issue with shared grounds is then any wired connections to network, etc. Wireless would solve that one, if I needed network connections while I was doing scope stuff and didn't have the stack of four other machines going in the same room.

Older laptops are often free, or nearly so. They're probably a good solution to the floating ground issues as well.

I think I'll go look at what's needed to make an opto-isolator USB dongle with a side-fed power system. There may be a powered hub that can just be (ab)used for that.

[R.G.]

Never mind. They already exist, just pricey. Analog devices has a single-chip solution that like most AD chips is probably hard to find. Existing isolating hubs, cables, USB-fiber-USB, etc. are there. Now we're just haggling over the price.

[MoltenVoltage]

Here's one that uses the AD chips for $78

http://www.ebay.com/itm/CONVERTER-MODULE-USB-USB-ISOLATION-iCoupler-ADUM4160-ADUM5000-/270833210412

QA100 ($350) + $78 = $423 - still a bargain.

What's frustrating is that the chips are only $3.60 and $4.90, but you have to buy 100 at a time!
If those chips were available, the circuit is really simple (see fig. 9)
http://www.analog.com/library/analogDialogue/archives/43-06/USB_isolator.html

For under $15 in parts this could be built.

[defaced]

Would this work for what you're doing? http://www.circuitsathome.com/tag/adum4160
Looks like you can buy the board and the chips for a fair price: http://www.circuitsathome.com/products-page/usb-interfaces

[MoltenVoltage]

I sent them an email - it looks like the $25 kit comes with everything you need.  Strange that they are only using 1 of the 2 AD chips from the schematic, but I assume they have it figured out...

[QA]

Hi folks, my name is Matt and I'm the EE that designed the QA100. I just wanted to add a few words about USB isolation: It's really hard to do USB isolation on a 480Mbps USB connection, and the standard parts from ADI won't work here as they only work on full speed (12Mbps) links. The scope requires a high speed (480Mbps) connection to function. It's really tough to beat a laptop running on battery to get the full isolation. Another way that some motor customers are making differential measurements is via an AD629. This will measure the voltage drop across a sense resistor at up to +/-270V even though it runs off of +/-15V or so, so you can clip the "ground" of that to something at, say, 80V, and the other side to 90V, and 10V will come out the other side (it's a little trickier than but it's a great starting point). It's not full isolation, but it's enough isolation that anything powered from 120V is effectively isolated.

One note about USB and noise: There is nothing inherently noisy about USB. There are a lot of really good products that are USB-powered that are delivering amazing noise performance. We're right now working on a low-cost 24-bit 192Ksps audio analyzer that is resolving hundreds of nanovolts and powered purely from USB.

Some background on me: I'm a long-time albeit ocassional lurker, and dissassembled my first MXR distortion pedal in the late 80's while in school and thought "that's it?" and from there build a series of analog and digital effects for my own use based on an processor called the 8052AHBASIC and discrete logic. I'm at 6 guitars today, with my fav being a 80's heavy metal strat (I'm the original owner), playing through a Line6 amp and Behringer VAmp, but most of the effects anymore are VST plugins in Cakewalk. But I'll never forget the thrill of getting a new pedal.

I just wanted to make sure nobody went down a wrong path and spent money trying to use an isolator on the QA100.