Poll

What is your interest in the Hantek DDS 3x25?

I own one
36 (27.1%)
I am considering getting one
40 (30.1%)
Curious about the hack
16 (12%)
Just passing through
41 (30.8%)

Total Members Voted: 111

Author Topic: Review: Hantek DDS 3X25. Anyone own one?  (Read 289973 times)

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Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #200 on: July 11, 2011, 04:44:35 pm »
Quote
Great! Welcome to the club.  Please give us feedback also on the buying process and what the package was like when you finally received it.  Enjoy.

Thanks!  I bought it on eBay last night from testinstru - notified today that it had been shipped already.

I would LOVE mine to come with an external ROM for the Spartan3AN so that I could pull the firmware out and play with it - but I'm not too optimistic  ;)  But I'll certainly get the logic analyzer connected to the pins of it and the DAC to see exactly what the timing is like between the various pins - and how they are used - for example, the 18 pins used for the multiprocessor link - when each call is made to the DLL.
 

Offline saturationTopic starter

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #201 on: July 11, 2011, 05:50:34 pm »
I just perused eBay and now there are a more vendors today that have them for sale, even one USA seller, rikoinstruments.  If the unit isn't off production we have a chance of writing them to release some documentation in exchange for improving their software, as Velleman has done.  It should benefit their sales, so there is incentive for them to cooperate.

Thanks!  I bought it on eBay last night from testinstru - notified today that it had been shipped already.

I would LOVE mine to come with an external ROM for the Spartan3AN so that I could pull the firmware out and play with it - but I'm not too optimistic  ;)  But I'll certainly get the logic analyzer connected to the pins of it and the DAC to see exactly what the timing is like between the various pins - and how they are used - for example, the 18 pins used for the multiprocessor link - when each call is made to the DLL.

Best Wishes,

 Saturation
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #202 on: July 21, 2011, 01:00:25 pm »
I received my DDS3X25 today.  All seems to work fine - and as previously described here.  I looked inside - same v1.4 PCB and same chips wiped with the exception of the USB controller - which, as Tinhead pointed out in a previous message, was a STM32F103Cx.  What's funny is that they wiped the DC-to-DC converter markings instead - so I think their mind was wandering for a moment ;)

Since the Sync Out is problematic, I wanted to compare it versus Digital Output 11 - which (in generator mode) is the high-order bit of the Waveform Pattern.

First image is a direct comparison - Channel 1 = Sync Out / Channel 2 = DO11

Second image shows DO11 superimposed on a 1MHz triangle wave output from the DDS3X25.  Notice that it changes state at zero crossings of the output waveform, unlike the Sync Out.  That means by putting a jumper between DO11 and any of the Digital Inputs (0-5), it might be possible to write sweep software which changes frequency only at zero crossings - avoiding much of the glitching that might happen otherwise.

Third (Sync Out) and fourth (DO11) images show a single shot 1MHz sine wave triggering a single sweep of the scope.  Sync Out does not appear to respond correctly, but D011 does - and, the period is 1/2 that of the output waveform.

Fifth image shows a 75MHz sine wave along with the DO11 output.  Unlike Sync Out, there is no glitching or out of step problem.

Note - all of the measurements were made with the following setup:
Waveform Output and Sync Out through BNC cable terminated with 50 ohms at scope.
DO11 Output through a ribbon cable (no shielding), then alligator-clipped to a BNC cable terminated with 50 ohms at scope.

When I find some more time, I will get inside with a logic analyzer - and try to glean some better information about what the firmware is doing with various control lines.
« Last Edit: July 23, 2011, 09:51:49 am by marmad »
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #203 on: July 21, 2011, 02:50:32 pm »
dude!
1) save as png or jpg. those bmp's can easily waste half a meg on dave's server. and bandwidth of thousands others.
2) enable frequency counter on your scope so i dont have to take out my calculator
3) retry at odd frequency, like 3MHz, 33MHz, 74.7MHz. 1MHz and 75MHz are known to be "Synch Out" stable
4) How do you manage to output single pulse? teach me the code!
5) How do you manage to sweep at zero crossing by shorting D11 to input? pls explain in detail start from PC App down to signal generation.
6) By right D11 is just least significant digital value of what we see analogically in "Output", so by right it should follow (in synch) with "Output" at any freq, as said, retry (3)
7) Dont quite understand whats the blue trace on pic #3 and #4.
8} Thanks for the report. Hope to hear again.
9) Cheers ;)
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline saturationTopic starter

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #204 on: July 21, 2011, 05:28:57 pm »
Great job marmad, a lot to digest, so more later.  Was your purchase experience without a problem? I presume so as you didn't mention it and you went straight into putting it to work  ;D .
Best Wishes,

 Saturation
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #205 on: July 21, 2011, 05:44:29 pm »
Quote
1) save as png or jpg. those bmp's can easily waste half a meg on dave's server. and bandwidth of thousands others.

Sorry! I would normally... I just spaced out  :P - Just changed them to pngs  ;)

Quote
3) retry at odd frequency, like 3MHz, 33MHz, 74.7MHz. 1MHz and 75MHz are known to be "Synch Out" stable

Done - see below.

Quote
4) How do you manage to output single pulse? teach me the code!

Unfortunately, it doesn't seem to be able to be done reliably with just code (at least I can't get it to repeat more than a few times) - it seems to need a real hardware trigger to be consistent.   But you can do it a crude way in software; for example,  use Hantek software, select Single Wave, then click Ext Trig over and over again.  After a few clicks you will get a transition glitch which will send the wave.

But the correct, reliable way is to give it a real trigger.  So I took D011 output again (this time set to Programmable Output - not Pattern Generator) and I fed it into the Trig In (see photo).  Then every time you change the bit high (or low with falling edge) it sends the waveform. But this is only needed for consistency - software method above is fine for testing.

Quote
5) How do you manage to sweep at zero crossing by shorting D11 to input? pls explain in detail start from PC App down to signal generation.

I haven't tried it yet - only theoretical -- but for example:

Put a jumper wire from D011 pin to DI0 pin on front of Hantek - then in a silly recursive loop example:

:startSweep
    Dim startFreq as Double = 1000
    Dim lastFreq as Double = 100000
    Dim stepAmount as Double = 1000
    Dim stepPeriod as Integer = 100
    DDSSetFrequency(hWnd, startFreq, g_nWavePointNum, g_nWavePeriodNum)
    DDSDownload(hWnd, arBuffer(0), g_nWavePointNum)
    Gosub newSweepFreq(startFreq + stepAmount )
end

:newSweepFreq(start)
    Dim digInput as Integer = 0
    ' Have to have some code here to wait the step period first
    If start > lastFreq Then Return
    ' Wait through approximately one high and one low of DO11 - in other words, 1/frequency
    Do Until (digInput)
      If NOT DDSGetDigitalIn(hWnd, digInput) Then Exit Sub  ' unplugging DDS3X25 would break out of permanent loop
    Loop
    Do Until (NOT digInput)
      If NOT DDSGetDigitalIn(hWnd, digInput) Then Exit Sub
    Loop
    DDSSetFrequency(hWnd, start, g_nWavePointNum, g_nWavePeriodNum)
    Gosub newSweepFreq(start + stepAmount )
    Return
End Sub

I will try it with your source code base sometime in the next day or two - but if you manage to do it first, let me know!!

Quote
6) By right D11 is just least significant digital value of what we see analogically in "Output", so by right it should follow (in synch) with "Output" at any freq, as said, retry (3)

Almost right... D011 is the MOST significant bit of the DAC - so it will have the exact frequency (but offset 180 degrees) of any simple waveform out (sine, square, triangle, saw) as long as you have amplitude at maximum (+3.5) so that the DAC is swinging peak-to-peak.

Quote
7) Dont quite understand whats the blue trace on pic #3 and #4.

Blue trace shows what (#3) the Sync Out does when you use single wave output; (#4) D011 does when you use single wave output (in Pattern Generator mode at full-scale).

Quote
Was your purchase experience without a problem?

Yes, saturation - testinstru (from eBay) is a great seller - good communication - fast shipment - and well-packed.
« Last Edit: July 21, 2011, 05:53:53 pm by marmad »
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #206 on: July 21, 2011, 06:31:32 pm »
I will try it with your source code base sometime in the next day or two - but if you manage to do it first, let me know!!
sorry i'm not in the "state" or mood. i'll be looking forward for your result. but iirc, the signal wont get changed/updated even at frequency level by calling DDSSetFrequency only. you have to call both including the DDSDownload, ie change both frequency and data to get the signal or sweep working/updated. and i suspect there will be usb latency/delay issue that make zero crossing sweeping unreliable. but i hope u'll get different result. i can see hack possibility by feeding the digital output to trigger in your last picture. keep it up, and dont blow anything. :P
« Last Edit: July 21, 2011, 06:40:53 pm by Mechatrommer »
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Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #207 on: July 22, 2011, 01:04:18 am »
Quote
keep it up, and dont blow anything.

I thought I did earlier  :o  It's really possible to lock this thing up so badly that you have to unplug the power for awhile to bring it back to working order.

Quote
the signal wont get changed/updated even at frequency level by calling DDSSetFrequency only. you have to call both including the DDSDownload

Did you play around with the undocumented commands: DDSGetDivNum and DDSSetDivNum?  They are clearly effecting the clock divisor somehow, but I haven't been able to figure them out.  One thing I did discover though - if you use DDSSetDivNum, you can use DDSSetFrequency immediately after to change the frequency (without using DDSDownload), but the frequency is not exactly what you expect - it's some combination of SetDivNum and SetFrequency which I can't comprehend.  I haven't been able to manage to call DDSGetDivNum correctly to retrieve data or I could probably figure out the combination. 

There are also these other undocumented commands in the DLL (most likely related to Hantek's 8060 Scope/DMM/Signal Generator):

DMMAC_10A
DMMAutoACV
DMMAutoAC_mA
DMMAutoDCV
DMMAutoDC_mA
DMMAutoOHM
DMMCap
DMMContinuity
DMMDC_10A
DMMDiode
DMMManualAC_600V
DMMManualAC_600mA
DMMManualAC_600mV
DMMManualAC_60V
DMMManualAC_60mA
DMMManualAC_60mV
DMMManualAC_6V
DMMManualAC_800V
DMMManualDC_600V
DMMManualDC_600mA
DMMManualDC_600mV
DMMManualDC_60V
DMMManualDC_60mA
DMMManualDC_60mV
DMMManualDC_6V
DMMManualDC_800V
DMMManual_600KOHM
DMMManual_600OHM
DMMManual_60KOHM
DMMManual_60MOHM
DMMManual_6KOHM
DMMManual_6MOHM
DMMReStart
DMMRead
DMMRel
DMMTest
DMMsAC_10A
DMMsAutoAC_mA
DMMsAutoDC_mA
DMMsDC_10A
DMMsManualAC_600mA
DMMsManualAC_60mA
DMMsManualDC_600mA
DMMsManualDC_60mA
DMMsRead

It seems possible that Hantek, to save design and programming time, might be using the Multiprocessor Link pinouts (3X25) on the FPGA for the ADC conversion pins (8060).  Figure out the pins and circuitry and you could add even more hardware onto our little box  ;D
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #208 on: July 22, 2011, 01:20:22 am »
i did notice DDS*etDivNum function but dont know how to call with correct parameters. i didnt notice though the many list you provided, i dont have the tool. but since i dont have the proper parameters type and count, so i just leave them. i dont have enough time and power to reverse all of them. i hope you can come up with something.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #209 on: July 22, 2011, 01:28:47 am »
I sent Hantek an email saying my company needs more accuracy in the software we are writing for the device, and is it possible to know how to use the DDS*etDivNum functions.  I don't really expect a response - but who knows - stranger things have happened.
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #210 on: July 22, 2011, 03:50:04 pm »
Well, as I start to play around with controlling the DDS-3x25, I start to realize why it is so much cheaper than other devices in the same range.  I hadn't really looked closely at the software before, but now it starts to become clear.

I don't think the Hantek could be described as true DDS (Direct Digital Frequency Synthesis) at all - that is, if you define important processing blocks like a phase-accumulator and a waveform look-up table to be integral parts of DDS. The Hantek is lacking those things, but it seems it tries to mimic those functions (which should be in hardware) with the upper level software.  Hence the source of the glitching and the jitter and the lag times.
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #211 on: July 23, 2011, 12:17:58 am »
yes its just fpga, dac and an op amp. do you have link to a proper DDS architecture?
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #212 on: July 23, 2011, 12:48:35 am »
Quote
do you have link to a proper DDS architecture?

Link? you mean like: http://zone.ni.com/devzone/cda/tut/p/id/5516  - or -  http://www.analog.com/library/analogDialogue/archives/38-08/dds.html  - or -  http://en.wikipedia.org/wiki/Numerically-controlled_oscillator ?

I didn't understand exactly what the Hantek was doing until I started trying to control it.  I thought they had implemented the phase accumulator inside of the FPGA. Whoever designed the circuitry and wrote the firmware for the Hantek are idiots!  The functions are so badly implemented; I thought you could at least set a sample length (up to 4096) and a frequency - instead, it tells you how long the sample length has to be!  Plus, there is no direct control of the clock or a lookup table or... well, pretty much all the stuff of DDS.  But you already know all of this.

They aren't really being truthful in their promotional material; for example, the manual says:
"DDS-3X25 adopts the DDS technology so that it has the advantages of high frequency accuracy, high waveform resolution, high reliability, and wide software support."

Now I have to decide whether to keep it or resell it and get the Velleman, which is true DDS (see attached block diagram), but slower,  and costs about € 15 more.
« Last Edit: July 23, 2011, 01:01:02 am by marmad »
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #213 on: July 23, 2011, 11:57:12 am »
oo ok. quite a rant, if you happen to get the velleman, dont forget to do a review and tear down ok? ;)
btw, what do you expect the black box (below) will be, ie the phase accumulator, look up table and frequency selector (in another link)? a bunch of discrete components? or another specialized chip?


and yes i agree, their firmware and pc software writers are idiot they dont have a clue on signal generator usage, no user frequency tunable while maintaining waveshape, and the DDSSetFrequency returns strange number of points value to be used, it doesnt use full potential 4K points, mostly only half of it. but there's workaround for the later, ie you can pass the DDSDownload with any number of point you want up to 4096 points, but the drawback you have to calculate the Output frequency will be on your own and not in synch (your hack might give some hope). on hardware side i'm not sure about their idiocy, but i believe its the simplest design we can have, hence probably the cheaper price albeit high frequency capability, since i've made a tear down photos and not get any bad reply from experts. rufus here did teardown photos on his £900 AWG showing proper circuitry.

btw off topic, while looking for logic analyzer, hantek also got LA5034, 34 channel at whooping 500MSa/s, $200++ reused their 3x25 housing just different printing. i wonder whats inside, maybe just another fpga feed by 34 LA input. dont ask about their SW crappiness, its proven here. but will it be a good buy? if we really need a fast sampling LA? i dont know but i would like to hear some advice.
http://cgi.ebay.com.my/34CH-500MHz-USB-PC-Digital-Logic-Analyzer-HANTEK-LA5034-/310278713967?pt=BI_Analyzers&hash=item483e0d726f
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #214 on: July 23, 2011, 12:20:35 pm »
Quote
oo ok. quite a rant

Ha, ha... yes... up too late last night frustrated with trying to control the damn thing.  But I'm back at it today - testing some more  ;D

Quote
btw, what do you expect the black box (below) will be, ie the phase accumulator, look up table and frequency selector (in another link)? a bunch of discrete components? or another specialized chip?

Definitely hardware -- it can just be a cleverly programmed FPGA - that's how Velleman does it - their schematics are public and published.  That's why I thought that the Hantek did something similar.

Quote
and the DDSSetFrequency returns strange number of points value to be used, it doesnt use full potential 4K points, mostly only half of it.

Yes, when you use DDSSetFrequency, it actually sets a clock divider (immediately) then tells you what sample length to create for that clock rate.  But I thought we could get around the latency problems a bit by creating a lookup table in software memory, then just appplying amplitude and offset before DDSDownload. What do you think?

Quote
on hardware side i'm not sure about their idiocy, but i believe its the simplest design we can have, hence probably the cheaper price albeit high frequency capability,

Well, as I mentioned above, they could have programmed their FPGA for true DDS - but you're right that they probably couldn't have gotten the high speeds if they had done that.  And I think for the sales, they were just interested in the highest speed numbers - not true or perfect DDS.

Quote
btw off topic, while looking for logic analyzer, hantek also got LA5034, 34 channel at whooping 500MSa/s

Yes, I saw this... check your messages for more.
« Last Edit: July 23, 2011, 12:22:25 pm by marmad »
 

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #215 on: July 23, 2011, 12:39:42 pm »
The specs for that LA sounds close to the Intronix LogicPort, I wonder if it's a clone.

Note that software is critical for a PC-based LA, triggering, decoding and searching through signals are essential for operating an LA. I wouldn't buy a LA without first trying the software. I hated the Zeroplus software, for example.
 

Offline saturationTopic starter

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #216 on: July 23, 2011, 01:19:17 pm »
Nice discussion.  I see it a little differently, what we want out of the 3x25 is a function generator with defined distortion and stability in its frequencies, how this is done is another thing.

If this can be done cheaply by a hodge podge approach yet still provides the primary functionality, then its really a good thing.  I think we've seen its strengths and weaknesses as we continue to dissect it.

I've seen 'bad' analog designs by Horowitz and Hill's criteria such as in preamp stages that are in real products, but they work, so time has proven these to be cost effective.   One example of those is the fan speed controller on the Atten 858D workstation, dissecting it to make it safe also made me laugh.

The Atten 858D workstation is well discussed on eevblog, it really provides stable output heat but not a true scaled measured flow rate, but it drops the cost of hot air workstations 10X against a true brand name, and its 1/3 cheaper than a even knock off Chinese hot air workstation ... its a design unique to Chinese gear as this Hantek is.  All they did is take the controller circuit similar for the Hakko 936 soldering station, and used it to control the heating element of a hot air gun; then they put a variable wire wound pot in a 24VDC circuit to simply drop the supply voltage for the fan, for 'variable' control, how goofy is that?  But it works!  Excess power is dropped into the pot and is wasted,  but the total power of this DC circuit is < 1 watt, and the pot never becomes hot to touch at the lowest speed setting, so it should be reliable if the transformer doesn't fail.

Of course, it has its unfixable problems.  You have line voltage in the handle, which is not allowed in many industrial setting to avoid shock hazard, they prefer DC in hand tools.  But then, hot air guns are allowed by industry for commercial paint stripping, in many powertools, and in consumer items as hair dryers, so why not in a hot air workstation in a non non-ISO certified setting?

Which brings us back to the 3x25.  What more can be squeezed out of it to improve or extend its function generator capabilities?  But if you need it to study true DDS technology I think you've shown its not.




Best Wishes,

 Saturation
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #217 on: July 23, 2011, 01:39:19 pm »
Quote
If this can be done cheaply by a hodge podge approach yet still provides the primary functionality, then its really a good thing.  I think we've seen its strengths and weaknesses as we continue to dissect it.

True.  If I can just get it to output a stable sweep sequence, I will be fine with everything else.  And it may end up working - I'm trying a few tricks today.

But it is important to point out that Hantek is saying they use DDS technology in the device - and they're not really doing so.
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #218 on: July 23, 2011, 01:55:02 pm »
But if you need it to study true DDS technology I think you've shown its not.
i think it is, from all my (limited) reading and latest links above. DDS only convert digital data into analog data (wave) what else does it do? the only thing lacking imho in 3x25 are:
1) adjustable frequency or gain whatever on hardware level (not in fpga)
2) filtering on the output analog signal to reduce noise.
3) good fw implementation in fpga (or pc? ie dll or usb comm) to mimick/simulate (whatever your definition) a DDS.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline saturationTopic starter

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #219 on: July 23, 2011, 02:05:53 pm »
I hope you succeed, we will all be merry!  For the bolded items, I couldn't agree more, but we read so many untruths in advertising and worse the spec sheets, from many China branded items that its not worth your effort to take their specs seriously; we all ended up reconfirming performance to see its true capabilities, its a similar story with the Atten 858D workstation story I posted. 

Before I bought mine, early in this thread, I scouted other users who did the initial testing for me.  I think a Japanese radio restorer was using it to repair AM/FM radios, which at least told me it provided a usable output to the top of FM,  ~ 100 MHz.


Quote
If this can be done cheaply by a hodge podge approach yet still provides the primary functionality, then its really a good thing.  I think we've seen its strengths and weaknesses as we continue to dissect it.

True.  If I can just get it to output a stable sweep sequence, I will be fine with everything else.  And it may end up working - I'm trying a few tricks today.

But it is important to point out that Hantek is saying they use DDS technology in the device - and they're not really doing so.

Best Wishes,

 Saturation
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #220 on: July 23, 2011, 02:07:08 pm »
True.  If I can just get it to output a stable sweep sequence, I will be fine with everything else.  And it may end up working - I'm trying a few tricks today.
as long as sweeping function is concerned, its workable, unless during the transition, you just have to wait a little bit before analyzing your circuit behaviour. you get what you pay, you've been warned by me (previous post) about the sweep function long before you buy this stuff. are you sure the velleman is truly stable on sweep? you may end up having unperfect sweep with slower frequency signal :P who knows. to get a perfect sweep i think you need to pay multiples of 3x25 price. maybe our next mission (hack) is to rewrite the fpga! and usb communication :P
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #221 on: July 23, 2011, 02:40:09 pm »
Quote
DDS only convert digital data into analog data (wave) what else does it do?

No, no... Mecha - you're wrong.  You're just talking about digital to analog conversion.  DDS is more specific - there aren't multiple definitions - and there are certainly parts of the process missing from the Hantek, such as:

1) No lookup table -- every true DDS device I've seen has this as a base - minimum: sine, square, and triangle at full sample length stored in the device.  No need to download data except for AWs.
2) No phase register and accumulator of 2^44 minimum -- think of this kind of like the clock divider plus the bits of vertical resolution -- this is the most important part, since true DDS yields precision in at least the 0.01% realm - not 0.1% like the 3X25 - which is a factor of 10 worse - and accounts for the "non-stable" frequencies.  The 3X25 has a clock divider of approx. 2^16 plus 2^12 bits of vertical resolution.

True DDS works like this in software:  Tell device what waveform you want (e.g. triangle) and the amplitude, offset, and frequency to 6 digits of resolution (e.g. 1.2378Hz) - it does the rest.  Or download AW at full sample depth (e.g. 4096) and tell the device the amplitude, offset, and frequency - it does the rest.

Quote
you've been warned by me (previous post) about the sweep function long before you buy this stuff.

Ha - one always likes to believe one can find solutions where others have not  ;)

Quote
you sure the velleman is truly stable on sweep?

Oh yes, well documented.  But I will continue to see what I can do with this device before seriously thinking about jumping ship.

So, in that realm - attached are some PNGs of the digital outs of the Hantek clocked by the DAC.

1) The setup
2) 1MHz sine wave output - 3.5V pp - 0V offset -- notice sine wave of combined Generator outputs - and Gen11 as nice sync signal.  Also notice all the activity on the bottom 4 pins of the Multiprocessor link.
2) 1MHz sine wave output - 1.75V pp - 1.75V offset -- now there are glitches occurring in the Generator outputs - I have no idea yet why that is happening with a voltage offset.

Edit:  Just shrinking the images a bit for BW considerations
« Last Edit: July 23, 2011, 03:00:15 pm by marmad »
 

Offline Mechatrommer

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #222 on: July 23, 2011, 03:20:09 pm »
Ha - one always likes to believe one can find solutions where others have not  ;)
i know how that feels like ;) i hope you will
nice picture on your logic probing. strange i havent seen the glitch on 1.75V offset there, does it tally with digital data? ie can you see glitch in digital data as well?
you are tapping the dac pin? what is it clock? have you figure out what dac it is?
« Last Edit: July 23, 2011, 03:23:45 pm by Mechatrommer »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #223 on: July 23, 2011, 03:48:41 pm »
Quote
strange i havent seen the glitch on 1.75V offset there, does it tally with digital data?

Actually, I'm seeing other glitches now even without the offset - I'm starting to believe it's caused by the unbuffered, unpulled pins of the FPGA - but I will investigate further.  It might be crosstalk.

Quote
you are tapping the dac pin? what is it clock? have you figure out what dac it is?

Yep, pin 28 is the clock.  I think it is the DAC you discovered earlier (ISL5857 or ISL5861).
 

Offline marmad

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Re: Review: Hantek DDS 3X25. Anyone own one?
« Reply #224 on: July 24, 2011, 03:23:37 am »
I've been trying to work out how the hardware clock divider works on the Hantek...

It seems any frequency > 48,828Hz,  which is the maximum frequency the hardware could clock the full sample buffer (i.e.  clock / sample buffer = 200MHz / 4096 = 48,828Hz) follows the formula:

clock / (sample length / sample step) = fOUT
   where
sample length is an integer >= 2000 && <= 4095  [12 bits - it rolls to 4096 at 25MHz or above]
   and
sample step is an integer >=1 && <= 2047  [11 bits]

You can easily determine the frequencies the device can handle - for example:
200MHz / (2000 / 1) = 100,000Hz
The next highest frequency the device can do is:
200MHz / (3999 / 2) = 100,025Hz
then
200MHz / (3998 / 2) = 100,050Hz
and so on.  You can test this easily by feeding the output back into the frequency counter and trying to set the device to 100,010Hz in the Hantek software - it will instead go to ~100,025Hz.

The sample length and sample step numbers are what you get back when using the DDSSetFrequency command.  But I'm not sure how the divider works for <= 48,828Hz since the numbers returned in that case don't make sense in a formula.  I think that the undocumented DivNum setting is a part of the divider chain that's missing (in terms of math) for lower frequencies.  When you try to SetDivNum (undocumented - I'm not sure how to call it correctly so I just send it a Long variable), the clock gets very slow and the frequency drops very low.  Then you need to use SetFrequency to get it dividing correctly again.

Any thoughts, Mecha?
« Last Edit: July 24, 2011, 11:32:21 am by marmad »
 


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