EEVblog Electronics Community Forum

EEVblog => EEVblog Specific => Topic started by: T4P on September 24, 2012, 07:14:15 pm

Title: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: T4P on September 24, 2012, 07:14:15 pm
EEVblog #359 - QDSO Pocket Oscilloscope Review (https://www.youtube.com/watch?v=3im97Z7ceNI#ws)
So dodgy diyertool took down the item immediately
VERY SORRY FOR THIS STUPID PRODUCT! FORTUNATELY, WE INVITED DAVE AND MIKE TO POST THEIR PROFESSIONAL REVIEW. FACTS HAVE PROVED, THIS IS A FAILED PRODUCT.
HERE WE PROMISE: WE
WILL* NEVER SELL THIS PRODUCT AND PROMOTE PRODUCTS FROM THIS MANUFACTURER!

Yeah, some of my notes :
The STM8S is actually one of the fastest 8bit architectures around (or so ST claims) at least faster than Atmel/Microchip
And i wasn't partially surprised the UI is a steaming heap of S#@!
The power supply part was funny though, "Spare no expense"  ;D ;D ;D
It is such a terrible product that the UT81C although not exactly "pocket" sized does much better per dollar (the UT81C i suspect uses the same AD9288 clocked at 80MSPS)
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: SeanB on September 24, 2012, 07:38:16 pm
Caps on input are for probe compensation, but of course you cannot adjust them with the case closed.

OHL at his finest, wonder who will email the designer and ask why?????????
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: bullet308 on September 24, 2012, 07:59:19 pm
Seems this product is a few dozen man-hours and about $20 away from being useful.  :-/

I think they *almost* have something there. Well, maybe not *almost*...
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: AndyC_772 on September 24, 2012, 08:20:28 pm
So, will it blend?  ;D
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: ModernRonin on September 24, 2012, 08:34:24 pm
This product might have a snowball's chance in hell of being, well, *passable* in the very low end of the "starving college student" market, if only:

1) They QUIT INTENTIONALLY LYING about the specs. Even with a 100 MS/s ADC, we shouldn't expect it to be able to usefully display a signal faster than 10 MHz. Maybe, if everything inside was absolute duck's guts (which it clearly ain't) then *maybe* 15 MHz. But any product brief that includes the figure "40 MHz" is being intentionally deceptive, and the idiot marketing-droid who wrote the copy needs to be shot. In the head. Twice (to be certain).

2) They stop using the word "oscilloscope" to describe it. That word carries connotations of something that's a piece of scientific grade Test and Measurement equipment. This wasn't designed to be that, it didn't turn out to be that, and it never will be. Again, they need to QUIT LYING. This thing is a "waveform viewer", and not a particularly great one either. That's fine, as long as they stop calling it an oscilloscope. Call it what it is. Quit fucking lying.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: kkp on September 24, 2012, 08:36:17 pm
I was expecting Dave to bend out the common-mode suppression capacitor, and find it to be a 63V type (I found this to be the case in a china switcher). Y-rated capacitors are expensive. The factory will find a much cheaper substitute :-(.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: nitro2k01 on September 24, 2012, 09:33:09 pm
18:00-18:30 (The 20 MHz signal). The issue seems to be differing frequency response on the attenuator stages. Same-ish reason why you get overshoot on the square on some ranges. As Dave and Mike setablished, what a pile of
(http://www.talknerdytomelover.com/storage/poop.gif?__SQUARESPACE_CACHEVERSION=1294290311727)
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: lewis on September 24, 2012, 09:35:43 pm
I was expecting Dave to bend out the common-mode suppression capacitor, and find it to be a 63V type (I found this to be the case in a china switcher). Y-rated capacitors are expensive. The factory will find a much cheaper substitute :-(.

I noticed that too, absolutely lethal. It looks to me like a Guangzhou-Ning-Ping-Shin-Happy-Special-Condensor-Co-Ltd ceramic crossing the isolation boundary in that power supply.

Dreadful scope too. Absolute shite.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: hans on September 24, 2012, 09:40:36 pm
If I look at the DSO, it seems an approach where they can do the digital design (RAM, LCD controller, FPGA) but didn't spent any effort on the analog side of things. YEs the split ground plane, but I also learnt that the ground plane should be joined at the ADC in most cases. So go figure :).
And then they do have a working digital side, and put CRAP firmware on it. I mean, the Rigol 1052 has a 320x240 screen, and it can put 2 waveforms on it decently with good menu's.

The analog bandwidth ofcourse is complete bullshit. 200MS/s is 20MHz at most. But without a sin(x)/x interpolation, it doesn't look pretty at all.
The micro seems like only handling buttons. If you follow the board you see it moving straight across to the button side and just reading the damn inputs. Seems like they were short on I/O or something. Shift registers?

The A/D seems legit in that it's actually a dual 100MSPS ADC. Well, if it's not counterfeit. Mike pointed out the laser markings were not aligned straight...

Seems the input is pretty simple. Voltage follower (with diode clamps on the input, look at the size of those - how long would the survive an overload?), crappy voltage gain (with selector feedback resistor, great!) and into the A/D. Great, maybe they should buy a VGA/PGA next time.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Neilm on September 24, 2012, 09:57:49 pm
If I look at the DSO, it seems an approach where they can do the digital design (RAM, LCD controller, FPGA) but didn't spent any effort on the analog side of things. YEs the split ground plane, but I also learnt that the ground plane should be joined at the ADC in most cases. So go figure :)

There are some EMC experts who are against splitting the ground plane especially if there are tracks crossing the split as there pretty much all over it. I assume that the board was a dual layer not 4 layer.

It would be interesting to know if the noise that was seen had coupled through onto the input - those thick tracks going by the input caps looked like they might be carrying power so noise from the power supply could be coupled onto the input jack.

Neil
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: T4P on September 24, 2012, 11:47:28 pm
The analog bandwidth ofcourse is complete bullshit. 200MS/s is 20MHz at most. But without a sin(x)/x interpolation, it doesn't look pretty at all.
The micro seems like only handling buttons. If you follow the board you see it moving straight across to the button side and just reading the damn inputs. Seems like they were short on I/O or something. Shift registers?
I don't actually think you know about the johnson-nyquist sampling thereom. Explain why the Highest DSOX3000 is 1GHz at 5GS?
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: nitro2k01 on September 25, 2012, 01:46:07 am
I don't actually think you know about the johnson-nyquist sampling thereom. Explain why the Highest DSOX3000 is 1GHz at 5GS?
That's assuming that
1) you've got a perfect brickwall low pass filter with no roll-off
2) you're fine with having your f/2 Hz sine wave represented as a 2 samples per cycle square wave on the screen.
In practice you need a little headroom if you care about being able to see phase information in the recorded data. Whether that means an x5 or x10 sample rate depends on the rest of the design. In the case of QDSO the problem was obviously a crappy input stage. Or at least the first problem.
And also, I believe you mean the Nyquist-Shannon theorem.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: T4P on September 25, 2012, 08:17:41 am
I don't actually think you know about the johnson-nyquist sampling thereom. Explain why the Highest DSOX3000 is 1GHz at 5GS?
That's assuming that
1) you've got a perfect brickwall low pass filter with no roll-off
2) you're fine with having your f/2 Hz sine wave represented as a 2 samples per cycle square wave on the screen.
In practice you need a little headroom if you care about being able to see phase information in the recorded data. Whether that means an x5 or x10 sample rate depends on the rest of the design. In the case of QDSO the problem was obviously a crappy input stage. Or at least the first problem.
And also, I believe you mean the Nyquist-Shannon theorem.
Oh,damn. Brain not working in the morning.  ;D Well yeah, it was a SERIOUSLY crappy input stage.
Have you seen the UT81 series? The B version goes to 8MHz at x5 sample rate ... and it doesn't seem to be typical chinese crap
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: hans on September 25, 2012, 08:49:17 am
The analog bandwidth ofcourse is complete bullshit. 200MS/s is 20MHz at most. But without a sin(x)/x interpolation, it doesn't look pretty at all.
The micro seems like only handling buttons. If you follow the board you see it moving straight across to the button side and just reading the damn inputs. Seems like they were short on I/O or something. Shift registers?
I don't actually think you know about the johnson-nyquist sampling thereom. Explain why the Highest DSOX3000 is 1GHz at 5GS?

Lol, funny.
Of course I do. You need to sample  at 2x sps to capture a sine wave of frequency x Hz. But that's purely mathematical. I was talking about practical situations where a rule of thumb 10 samples per period is good. This scope doesn't obey. 4-5x sounds okay, but then at least have the scope designed for it.
I mean: anti-aliasing filters and decent drawing methods like sin(x)/x interpolation. Because at 5 samples per period, linear interpolation, it would probably look something like this:
(http://www2.tek.com/cmsrep/psrep/img/13298/A000_2739-L.jpg)
I don't know about you, but I call that nasty. Of course this view suggests a pure sine wave at a frequency pushing the boundaries of the scope.
We should actually care about the -3dB bandwidth of the scope, which should be situated at 40MHz and roll-of nicely.
But c'mon look at the input stage. Where is the bandwidth filter? Dave experienced HORRIBLE ringing at 10MHz square waves,.. that tells me the input stage doesn't have a very 'flat' frequency response.

Q(rap)DSO
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Psi on September 25, 2012, 08:51:43 am
I think what you want is something that folds in half.
One half is the screen and the other has thumb-wheel encoders for all your typical controls plus tack buttons for everything else.

So when you fold it out it really is pretty much like a normal scope, just smaller.

Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: george graves on September 25, 2012, 08:52:33 am
This review was almost silly(and yet - I enjoyed it!) - but it was just to review something bad for the sake of making fun of it - Ha!  Well....

Someone soon is going to nail this form factor with performance as-good-as-or/better then an entry level rigol - 640x480, 2 channel and a touch screen.  It's only a matter of time.

And it will be $150-$200 USD at the most.  I think even Dave will admit - the race to the bottom of test gear cost is on!  They'll be some duds, and some outstanding price/performance stuff along the way....now if we only had someone to test all this upcoming gear!  ;)

Great video BTW - and don't forget to click the "like" button!
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Psi on September 25, 2012, 10:48:37 am
Threw together a mockup of a folding pocket scope with proper controls.

However now i'm thinking it would be better to folder on the bottom rather than the right.
So the controls were below.

(http://psi.abcom.co.nz/ScopeA.jpg)
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: mikeselectricstuff on September 25, 2012, 10:55:54 am
Threw together a mockup of a folding pocket scope with proper controls

(http://psi.abcom.co.nz/ScopeA.jpg)
Horizontal format probably not good for handheld use - you want to be able to hold in one hand and reach most of the controls with a thumb.

Don't really need buttons or LEDs for AC/DC - these don't get changed often enough to justify the space.
Knobs don't need to be that wide - make them narrower and have more of them - at least x position and timebase, and y position/scale.
Maybe also push functions for time zero, autoscale, zero and ac/dc select respectively.

Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Psi on September 25, 2012, 11:32:16 am
Yeah, there are lots of layout options.
Folding on the bottom would definitely be better.

I probably did go a bit overboard on the buttons.

Those thumbwheels were just what i found Google image searching.
Any control would work so long as it's analog and easy to use.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: AndyC_772 on September 25, 2012, 11:38:34 am
I wouldn't go with a pocket format at all, it's uncessary and results in too many design compromises that do limit its usefulness. The smallest that a scope needs to be is one which is small enough to hold one handed or to find room for on a cluttered desk.

I'd go with a deeper design, with proper BNC probe connections on the sides for its 2 channels, and a battery that's big enough to power more capable electronics and still maintain a decent lifetime. A scope with a flat battery is useless.

However, in case of a flat battery I'd have the option of dc power from an external brick, with an isolated internal power supply that allows it to make floating measurements even when it's not running on its internal batteries. USB power might be a possibility.

I hate touch screen scopes, so I'd have a few proper controls on the front panel - maybe a single rotary encoder and a bunch of hard buttons which control what it does. From the front it might look a bit like a Philips Pronto TSU9600 (google it).

2 channels means it's possible to do serial decoding on I2C, CAN and UART interfaces, or one direction of an SPI port at a time. The serial decode feature would come as standard, meaning it might actually be cheaper in some cases to buy a handy miniature scope than it would be to add serial decode options to a conventional bench scope. Costly serial decode options are a complete rip-off, IMHO.

The hardware would be able to do an intensity-graded display, to give a much better impression of irregular waveforms. (The extra memory and FPGA resources would be the main driving force behind needing the deeper form factor - it's not trivial to do this by any means).

My miniature scope wouldn't be particularly cheap, simply because it can't be both cheap and right. Existing toy pocket scopes have proved this already. A scope that doesn't give a true, useful indication of a waveform is useless, and therefore a waste of money at any price.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: KedasProbe on September 25, 2012, 11:43:46 am
Nice video (a bit too long), building up to the moment we know we were all waiting for: Throwing the thing away.
Maybe hitting it with a hammer would have been nice to end the video  ;D
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: TheWelly888 on September 25, 2012, 12:26:11 pm
It is unbelievable that someone decided to sell a device with an on/off button that doesn't work as such!! Such counterintuitive products are very very annoying if you don't use them everyday.

A shame that such a facepalmy product actually went to market! But I am glad that the main dealer withdrew the device before it caused any more grief.

Well done Dave and Mike!

Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Psi on September 25, 2012, 01:35:38 pm
The "pocket" format is what makes it useful.
If it's too big to fit in my pocket then i might as well use a proper scope.

The idea is to have a scope you can take anywhere, something that goes with one of those tiny pocket multimeters.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: mikeselectricstuff on September 25, 2012, 01:52:31 pm
Quote
I wouldn't go with a pocket format at all, it's uncessary and results in too many design compromises that do limit its usefulness. The smallest that a scope needs to be is one which is small enough to hold one handed or to find room for on a cluttered desk.

I think there are probably two useful product points for the ultimate portable scope:

"Pocket" - for quick testing where a DMM isn't enough. Maybe 60MHz, very small & light, basic functionality, maybe 1 and 2 channel options. Chargeable from USB. dedicated probes with small connectors acceptable. UI probably touchscreen and/or side mounted edge-wheel encoders. Must be fully operable one-handed. >2 hour battery life.

"Portable" - cose to full features (comparable to, say. rigol 2000 & Agilent MSOX2000), intensity graded display, at least 200MHz with comprehensive triggering options and protocol decode.
Option for probes isolated from each other (extra cost option as many people won't need it). Small and light enough to use handheld for short periods, with basic controls operable handheld- about the size of the OWON - the Agilent portables are too big and heavy.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: jpelczar on September 25, 2012, 02:45:03 pm
If they opensourced the scope's firmware, I'm sure people would improve it (both in FPGA and uC)
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: CesarEscudero on September 25, 2012, 03:04:03 pm
The "real" product...

(http://i00.i.aliimg.com/photo/v0/295044486/cheap_mp5.jpg)
(http://digitaleveryone.com/UserFiles/MP5-player-China-MP5-player-Cheap-3-Inch-TFT-2GB-with-Mp3-Mp4-a.jpg)
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: free_electron on September 25, 2012, 04:42:47 pm
Explain why the Highest DSOX3000 is 1GHz at 5GS?
to restitute a waveform you need more than 2 points .... if at 1Ghz all you have is 2 points you have no clue if it is a sinewave, a squarewave or a triangle or something complex...

if you want to really see a 1GHz signal... make sure you are sampling in the 100Gs/s range. that still only gives you 100 samples for a period ... good luck trying to visualize , let's say a gsm antenna signal..

@psi : why knobs ? just gimme a damn touchscreen, get rid of the buttons and make the screen larger and higher resolution. 320 by 240 just doesn't cut it anymore in 2012 ... use a PSP screen.

. 2 finger pinch in vertical to control gain  in horizontal to control time base. swipe to scroll ( set trigger point)
hold finger on trace and move for vertical positioning.
three fingers set trigger level.
double tap on trace sets trace as trigger source.

no buttons needed. some softkeys on the right can pull up a menu to control things like dc/ac and other fany stuff.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: mikeselectricstuff on September 25, 2012, 05:09:22 pm
Quote
@psi : why knobs ? just gimme a damn touchscreen, get rid of the buttons and make the screen larger and higher resolution. 320 by 240 just doesn't cut it anymore in 2012 ... use a PSP screen.

One reason is you often need to twiddle while looking at a live waveform (and so don't want fingers in the way) , possibly one handed (maybe also holding the scope in the same hand) while the other hand is holding a probe.
Touchscreen is probably better than buttons, but physical knobs are king for the basic functions that are used all the time. 
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Bored@Work on September 25, 2012, 05:11:59 pm
@psi : why knobs ? just gimme a damn touchscreen,

Because touchscreens are susceptible to accidentally touching something, and therefore mis-adjusting something.  Touchscreens can't be operated with only 'one eye' on the scope (and the other on the DUT), because you have no tactile feedback what you are adjusting, and instead you really need to observe the screen.

Quote
. 2 finger pinch in vertical to control gain

Oh dear, oh dear, oh dear. One of the worst gestures, because it requires to either hold the instrument with one hand and pinch with the other (who is holding the probe then?), or to place the instrument on some surface where it sits stable. Both disastrous for a handheld/pocket instrument. 
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: free_electron on September 25, 2012, 05:27:21 pm
let's make a scope that uses a heads up display. now that would be cool. just wer a pair of glasses and the scope info gets overlayed on your vision.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Ketturi on September 25, 2012, 05:27:44 pm
This is absolutely waste of engineering. It think it's possible to make handheld DSO with same specs and price, but more friendly user interface, and it would be then useful product(not in everyday use but in quick debugging and diagnosing on the field). But using cheapest mp3 chase, comeon. We have amazing smartphones and other handheld device, and with integrated circuits and mass production their prices have come down. Why not make, say in example, android device with integrated scope and logic front ends, every engineers pocket buddy ;3 For engineers and technicians not working front of lab-desk, it is sure frustrating carrying full arsenal of test equipment, so it is too for hobbyist who can not afford high end portable devices, but still occasionally need work away from home. I have once taken my old "portable" kenwood analog scope with me, and it was last time. If somebody wants to use it or wants me to fix something, i do not do home visits.

Dave, why not give try to make affordable but still user friendly mini scope, ┬ÁDSO like the other ┬ÁDevices you have :)
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: quarros on September 25, 2012, 05:42:36 pm
Well there are some usable DSO-s out there that cheap enough.
Prime example: http://www.seeedstudio.com/wiki/index.php?title=DSO_Quad (http://www.seeedstudio.com/wiki/index.php?title=DSO_Quad)
Altough it is above 200USD. But at least it IS actively maintained on the software side.


I have to retract my statement above. Sorry it is crap too.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: grumpydoc on September 25, 2012, 06:52:39 pm
Quote
to restitute a waveform you need more than 2 points .... if at 1Ghz all you have is 2 points you have no clue if it is a sinewave, a squarewave or a triangle or something complex...

if you want to really see a 1GHz signal... make sure you are sampling in the 100Gs/s range. that still only gives you 100 samples for a period ... good luck trying to visualize , let's say a gsm antenna signal..

True, But.....

'scopes have always been specified by their 3dB bandwidth and attenuation of harmonic content past that point is always going to affect the display. Put bluntly a "1GHz" 'scope is never really going to make a good job of distinguishing a 1Ghz sine, square, triangle or something more complex.

In practice the frequency response of the analogue front end isn't a brick wall, so it's worth sampling at more than the 2x limit as that extracts a bit more useful information from the signal and helps avoid aliasing but 100x is just over designing the digital section.

Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: LaurenceW on September 25, 2012, 07:35:27 pm
c'mon Dave, get off the fence. Just tell us straight - is it any good?

My Kitchen table has a wobble, 'cos one leg is 7mm shorter than the other three. I may have a use for this device.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: ejeffrey on September 26, 2012, 12:36:28 pm
if you want to really see a 1GHz signal... make sure you are sampling in the 100Gs/s range. that still only gives you 100 samples for a period ... good luck trying to visualize , let's say a gsm antenna signal..

That is complete nonsense.  People don't seem to realize the purpose of oversampling.  They do absurd things like drawing one period of a sine wave with 5 points and connecting the dots, then point to the infidelity of the waveform as evidence of insufficient sampling.  That is absolutely wrong, and reveals a woeful lack of understanding of digital signal processing -- that is just evidence that they are using the stupidest possible interpolation filter.

The purpose of oversampling is to avoid aliasing.  Your bandwidth limiting filter doesn't not have a brick-wall response, so some frequency components above the 3 dB point will pass through it.  The purpose of oversampling is to make sure those frequency components are not aliased down into the passband.  You get a little information about these components as well, but the primary purpose is simply to avoid getting _misleading_ information due to aliasing.  Want to find out how much oversampling you need?  You  look at the analog bandwidth and find the frequency where the filter has rolled off enough to be negligible.  Then double that, and that is your minimum sampling rate.  If you have a 1 GHz scope that needs 100 GS/s sampling rate, it has a tragically bad analog front end.

GSM is a particularly terrible example, as the spectrum is confined to (relatively) narrow frequency band compared to digital logic signals.  While a 1 GHz logic signal has spectral content much higher than that, a 900 MHz GSM signal does not.  Therefore, hardly any oversampling is required even if the AFE rolloff is very weak because there is simply no signal at the higher frequencies. 
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: EEVblog on September 26, 2012, 01:01:40 pm
c'mon Dave, get off the fence. Just tell us straight - is it any good?
My Kitchen table has a wobble, 'cos one leg is 7mm shorter than the other three. I may have a use for this device.

A dried out dog turd would make a far superior support for your kitchen table  ;D

Dave.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: kvresto on September 26, 2012, 09:02:35 pm
Dave in your blog you spoke about how bad the front end was using the 4051 switch, and it seems to be the way a lot of these do it yourself units are made.

Can you give us a bit of info on how to do it better?

,... and NO I dont have anything to do with this steaming pile of dog turd!!!
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: Dread on September 26, 2012, 11:57:40 pm
If they had done a better Job with the case and the button ergonomics this would be an ok product but right off the Bat they go and put it in a MP3 player case, that just sealed the coffin shut from the get go.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: JoannaK on September 27, 2012, 02:36:02 am
Dave in your blog you spoke about how bad the front end was using the 4051 switch, and it seems to be the way a lot of these do it yourself units are made.

Can you give us a bit of info on how to do it better?

,... and NO I dont have anything to do with this steaming pile of dog turd!!!

If you wander around this site, there are plenty of discussions about hacking/modifying Rigol Scopes.. The older one (was it 1052?) people have been activelly reverse enginering .. There seems to be full schematics of the front end floating around also (see link at the 2000 series teardown thread). I'm not saying that Rigol's front end would be best/preferred or optimal price/quality, but it's obvious these cheap portable-Dso -makers have lot to learn about analog enginering.

Besides schematics (part changes) there are other things (like board design, layout, screening, power supply etc) that will affect the analog parts.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: ModernRonin on September 28, 2012, 08:20:16 pm
Dave in your blog you spoke about how bad the front end was using the 4051 switch, and it seems to be the way a lot of these do it yourself units are made.

Can you give us a bit of info on how to do it better?

I can't speak for Dave, but I can tell you one component that would be a lot better than a 4051: an RF relay. This is just a small relay that has the switch part made in such a way that it interferes minimally with the signal passing through it - even at very high (RF) frequencies.

This isn't the only way, but it's a simple and obvious one. The reason they didn't use it is, of course, because of cost. A 4017 is dirt cheap. An RF relay isn't.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: FJV on September 28, 2012, 08:38:27 pm
Threw together a mockup of a folding pocket scope with proper controls.

However now i'm thinking it would be better to folder on the bottom rather than the right.
So the controls were below.

(http://psi.abcom.co.nz/ScopeA.jpg)

To be honest I "my pocket scope design" would be just a smart probe with a wifi / bluetooth connection.
The probe would send the measurements to your smartphone / tablet with an application for display, triggering, controls, etc.
Maybe you might be able to hook up several such probes to an electronic circuit and readout all on you smartphone wirelessly.

However designing such a thing is way, WAY, WAY beyond my skill. (absolute beginner 8))



Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: T4P on September 28, 2012, 08:47:49 pm
That's wank. Touchscreens are hopeless, i wouldn't want one at all.
Touchscreens are only for this generation's kids who thinks Apple makes the best phone and that they made touchscreens
And wireless ... forget about it. I want my scopes with knobs not some wanky wireless connection that i have to use my 8hour battery life for.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: FJV on September 28, 2012, 08:55:47 pm
That's wank. Touchscreens are hopeless, i wouldn't want one at all.
Touchscreens are only for this generation's kids who thinks Apple makes the best phone and that they made touchscreens
And wireless ... forget about it. I want my scopes with knobs not some wanky wireless connection that i have to use my 8hour battery life for.

I am sorry that telemetry technology, such as used in formula one cars, space exploration, defense, etc is just not good enough for you.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: M0BSW on September 29, 2012, 10:59:24 am
ha,ha,ha,ha I guess you don't like it then Dave, won't be rushing out to buy one ,unless they start giving them away with cornflakes, my telequipment D61A analogue scope may be old but it works, and I'll still have it when i buy a Rigol 1102e i think its called which I've been looking at , and dropping large hints to the Mrs, brillaint videoeven made the Mrs smile "what"
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: tom66 on September 29, 2012, 10:33:06 pm
Threw together a mockup of a folding pocket scope with proper controls.

However now i'm thinking it would be better to folder on the bottom rather than the right.
So the controls were below.

(http://psi.abcom.co.nz/ScopeA.jpg)

To be honest I "my pocket scope design" would be just a smart probe with a wifi / bluetooth connection.
The probe would send the measurements to your smartphone / tablet with an application for display, triggering, controls, etc.
Maybe you might be able to hook up several such probes to an electronic circuit and readout all on you smartphone wirelessly.

However designing such a thing is way, WAY, WAY beyond my skill. (absolute beginner 8))

I would like to see you fit a high speed ADC and FPGA onto something the size of a scope probe.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: batterypowerguy on October 11, 2012, 07:26:45 pm
Not sure why the usb charger is getting knocked so much, actually pretty decent quality given the likely price point (I would swag at about $2 usd). The TL431 is a voltage reference that is classically used to drive the opto  to get feedback across the isolation boundary. I have seen boards a lot worse looking than that which were supposedly TUV listed.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: tom66 on October 11, 2012, 07:36:25 pm
It's what's known as a two-transistor self-oscillating converter.

I don't like them because they have a tendency to go a little out of control with the output voltage shooting up to double or more of the rating.

Also, if you short the output, you blow the mains fuse.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: jeremybarker on November 10, 2012, 08:14:09 pm
"Not sure why the usb charger is getting knocked so much, actually pretty decent quality given the likely price point"

I wouldn't want it anywhere near me because just by looking at it you can be sure that it absolutely does not comply with any safety standards. I would bet that if you dismantled the transformer you would find that all that separates the primary and secondary windings is one or two layers of some nasty thin tape. You can also see on the board that the isolation clearance is a bit insufficient even for a 120V input. And it is most unlikely that the little ceramic capacitor connected across the isolation is safety rated in any way.
Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: TRIO_Smartcal on November 14, 2012, 09:47:47 pm
As Dave said in the review and tear-down, why waste your money on a dog-pile? 

As a test-equipment sales/service/calibration and rental company, we get offered products almost daily from (mainly Chinese) companies wanting to get into the Aussie market. We turn virtually all of them away.  The reason is not that we don't think we can make money on something, it is more about the overall value of the product.

This thread showing a product that is cheap but of low value is an opportunity to put forward something to think about when it come to buying at the bargain end of the market.

As an example, compared to the QDSO, there's scopes from us and our competitors that you pay a bit more for, but when you see what you get for that "bit" more money, you should pause for a bit of thought......

There's an old marketing-speak adage that goes:  (Value = Performance/Price + Service) 

For different people the 3 variables in the value equation have different levels of importance.  So my advice is don't just consider the price, (sub-consciously most people don't anyway otherwise we'd all be driving Great Wall cars), but actively look for value within what you can afford and in the long term you'll be better off.

It might be unfair comparing things like the QDSO to low-cost (real) scopes, but when for not a lot more cash you can get much more, then as Dave rightly says don't waste your money.

Here's an example of value vs price vs performance.....  Have a look at the scope on the link below. This scope is about the same price as a Fluke 170 series multimeter. Compare the amount of hardware you get for your hard-earned cash... then figure out who is making a bundle of profit out of you the buyer, and where are you getting the better value.

http://triosmartcal.com.au/siglent/2896-siglent-sds1022dl-25mhz-2-channel-widescreen-oscilloscope.html (http://triosmartcal.com.au/siglent/2896-siglent-sds1022dl-25mhz-2-channel-widescreen-oscilloscope.html)

A good question always to ask yourself is "can I get the same functionality for less and still feel comfortable with my purchase in terms of performance and service?"
Apply that to an oscilloscope and a DMM.

Big-Brand Digital Multimeter at $300 = 1 little LCD + 1 little PCB + Case + battery connector + battery + 1 knob + a 4-button keypad + input hardware + fuses
DSO at $300 =  Colour display, power supply, metal chassis, lots of knobs and buttons, USB etc.... simplistic but true...  You can get a good DMM for around $100 (see Dave's Extech videos) but can you get a similar scope for much less and still take it back to where you got it if it goes wrong?  It's not as easy.

So when diving down to the bottom of the waveform capture and display market, just considering hardware-cost alone, consider spending a "bit" more cash, and buy something decent from a reputable company with real people you can talk to, complain to, easily return goods to, (or even say nice things to) if necessary.

Here's a few of examples from the Aussie oscilloscope world.  Two are a similar price but different performance and one is a main brand with a higher price.   So play "spot the value...."

http://www.jaycar.com.au/productView.asp?ID=QC1932&CATID=97&form=CAT2&SUBCATID=1062#1 (http://www.jaycar.com.au/productView.asp?ID=QC1932&CATID=97&form=CAT2&SUBCATID=1062#1)

http://triosmartcal.com.au/1961-tekway-dst1102b-digital-oscilloscope-with-wide-screen-hd-display.html (http://triosmartcal.com.au/1961-tekway-dst1102b-digital-oscilloscope-with-wide-screen-hd-display.html)

http://australia.rs-online.com/web/p/digital-oscilloscopes/7344997/ (http://australia.rs-online.com/web/p/digital-oscilloscopes/7344997/)

Now I know this is not a technical post on this thread, and people will say I'm plugging our company, but we have worthy competitors out there in Aussie-Land that do the same as us and that should be recognised too. In the end we all need to spend our cash to get test equipment (except Dave of course) but this thread is a good opportunity from a supplier point of view to take the opportunity to suggest that you need to look behind the price, behind the brand, and fill in the value equation when choosing your purchases or that dog-pile might just end up being yours.








Title: Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
Post by: MarkDennehy on January 14, 2016, 10:59:31 pm
Sidestepping the whole DSO bit (and apologising for the CPR'ing of a dead thread) - where can you source the cases these guys were using? There's this raspberry pi-based project I'm mucking about with and that case or something similar might just be perfect for it...