Author Topic: EEVblog #359 - QDSO Pocket Oscilloscope Review  (Read 37818 times)

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Offline CesarEscudero

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #25 on: September 26, 2012, 01:04:03 am »
The "real" product...


 

Offline free_electron

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #26 on: September 26, 2012, 02:42:47 am »
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.
« Last Edit: September 26, 2012, 02:47:31 am by free_electron »
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Offline mikeselectricstuff

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #27 on: September 26, 2012, 03:09:22 am »
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. 
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Offline Bored@Work

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #28 on: September 26, 2012, 03:11:59 am »
@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. 
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Offline free_electron

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #29 on: September 26, 2012, 03:27:21 am »
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.
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Offline Ketturi

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #30 on: September 26, 2012, 03:27:44 am »
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, µDSO like the other µDevices you have :)
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Offline quarros

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #31 on: September 26, 2012, 03:42:36 am »
Well there are some usable DSO-s out there that cheap enough.
Prime example: 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.
« Last Edit: April 02, 2013, 06:16:40 am by quarros »
 

Offline grumpydoc

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #32 on: September 26, 2012, 04:52:39 am »
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.

 

Offline LaurenceW

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #33 on: September 26, 2012, 05:35:27 am »
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.
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Offline ejeffrey

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #34 on: September 26, 2012, 10:36:28 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. 
 

Online EEVblog

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #35 on: September 26, 2012, 11:01:40 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.
 

Offline kvresto

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #36 on: September 27, 2012, 07:02:35 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!!!
 

Offline Dread

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #37 on: September 27, 2012, 09:57:40 am »
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.
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Offline JoannaK

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #38 on: September 27, 2012, 12:36:02 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!!!

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.
 

Offline ModernRonin

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #39 on: September 29, 2012, 06:20:16 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?

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.
 

Offline FJV

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #40 on: September 29, 2012, 06:38:27 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.



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))



 

Offline T4P

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #41 on: September 29, 2012, 06:47:49 am »
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.
 

Offline FJV

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #42 on: September 29, 2012, 06:55:47 am »
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.
 

Offline M0BSW

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #43 on: September 29, 2012, 08:59:24 pm »
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"
« Last Edit: September 29, 2012, 09:02:26 pm by M0BSW »
no one would or will tell me how to delete this account
 

Offline tom66

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #44 on: September 30, 2012, 08:33:06 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.



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.
 

Offline batterypowerguy

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #45 on: October 12, 2012, 06:26:45 am »
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.
 

Offline tom66

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #46 on: October 12, 2012, 06:36:25 am »
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.
 

Offline jeremybarker

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #47 on: November 11, 2012, 07:14:09 am »
"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.
 

Offline TRIO_Smartcal

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #48 on: November 15, 2012, 08:47:47 am »
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

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

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.








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Offline MarkDennehy

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Re: EEVblog #359 - QDSO Pocket Oscilloscope Review
« Reply #49 on: January 15, 2016, 09:59:31 am »
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...
 


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