Review of Cheap DDS Function Generator UDB series (UDB1102, UDB1103, UDB1105)

[pullin-gs]

I needed a cheap function generator, so I took the risk and bought a UDB1105S on Ebay for $65 shipped.
The video mini-review is here:


There are 6 variations of the UDB11xx funtion generator that I know of:
UDB1102 (2Mhz) UDB1102S(2Mhz), UDB1103(3Mhz), UDB1103S(3Mhz), UDB1105(5Mhz), UDB1105S(5Mhz).

All support sine, square, triangle, an saw waveforms.
Waveform adustments include frequency, amplitude, and DC offset,and  %duty.
The maximum USABLE Mhz for ALL MODELS is 1Mhz for sqare, triangle, and saw waveforms.
The maximum sine-wave Mhz is 2, 3, or 5Mhz depending on which model you purchased.

All support a counter function, and a frequency (60Mhz max) counter.
All support standard output, a square-wave TTL output (3.3VDC), and an external input.
All support a -32dB attenuation button.
Power options vary depending on vendor....some have 5VDC inputs, mine has a USB input.
I powered mine off my OWON scope's USB port for tests.

The "S" models have a programmable "scanning" feature.
The frequency low and high points of the scanned range is settable.  The time between the low to high frequency scan is also settable.

Issues:
Two of the buttons were sticking...I had to open up the case and loosen the circuit-board mounting screws to eliminate binding.
The offset potentiometer is flaky....needs to be replaced.

My opinion is that this is a good budget function generator for work up to 1MHZ.  The scan feature is nice also, as is the TTL output.  The "toy" factor of the casing almost put me off to the point of not buying.  A plus about the case is that it is very compact in size, so it fits nicely in just about any tool bag.

Recommendation to the vendor:
Loose the Fisher-Price case.  If you come up with an enclosure with integrated power supply that is more along the lines of what other vendors use, this thing would sell like hot-cakes!

[saturation]

Thanks!  Very informative video.  Given competing function generators of similar performance its actually not bad for $65 delivered, not much can compete as a new product.  I think one can only do better getting a used FG

[T4P]

Thanks!  Very informative video.  Given competing function generators of similar performance its actually not bad for $65 delivered, not much can compete as a new product.  I think one can only do better getting a used FG

Unless it was DDS, then it's not apples to apples anyway this thing isn't cheap at all.
50$ is not what you call exactly cheap 

[pickle9000]

I ordered one last week (UDB1102 Z) what I'm interested in is can you save any settings, like frequency and waveform? It's very hard to understand the chinglish manual I downloaded.

...mike

[saturation]

The board is DDS, doesn't it say on the links?  The populated PCB alone without the casing goes for $25-40 on eBay.  You can easily check eBay for what is available to compete with this units capability.  The only main issue I have with it is quality of the generated waveforms in terms of frequency stability, amplitude stability and harmonic purity.  Some units are better than others for the same price, but not in this range.

The demo shows jitter worsening as it approaches 1 MHz.  A simple way to check jitter is leave persistence mode on your scope on, they leave it connected to the FG for an hour or so, if the curves are now much fatter, the width is ~ jitter width; if you see ghost patterns of waveforms elsewhere, the frequency drifts about, and if the amplitude is also fat, that's ~ Vout instability.

For harmonics, you can test it to your scope's limits by passing the waveforms to the scopes FFT, and looking for unexpected frequencies beyond a pure pure square, sine and triangular wave. 

Thanks!  Very informative video.  Given competing function generators of similar performance its actually not bad for $65 delivered, not much can compete as a new product.  I think one can only do better getting a used FG

Unless it was DDS, then it's not apples to apples anyway this thing isn't cheap at all.
50$ is not what you call exactly cheap 

[T4P]

The board is DDS, doesn't it say on the links?  The populated PCB alone without the casing goes for $25-40 on eBay.  You can easily check eBay for what is available to compete with this units capability.  The only main issue I have with it is quality of the generated waveforms in terms of frequency stability, amplitude stability and harmonic purity.  Some units are better than others for the same price, but not in this range.

The demo shows jitter worsening as it approaches 1 MHz.  A simple way to check jitter is leave persistence mode on your scope on, they leave it connected to the FG for an hour or so, if the curves are now much fatter, the width is ~ jitter width; if you see ghost patterns of waveforms elsewhere, the frequency drifts about, and if the amplitude is also fat, that's ~ Vout instability.

For harmonics, you can test it to your scope's limits by passing the waveforms to the scopes FFT, and looking for unexpected frequencies beyond a pure pure square, sine and triangular wave. 

Thanks!  Very informative video.  Given competing function generators of similar performance its actually not bad for $65 delivered, not much can compete as a new product.  I think one can only do better getting a used FG

Unless it was DDS, then it's not apples to apples anyway this thing isn't cheap at all.
50$ is not what you call exactly cheap 

I know it was DDS i was referring to the "used" FG you talked about

[pullin-gs]

OT:
While running through the FG tests, I came upon a few things that bothered me about THE SCOPE (!).
I think a new thread may be in order titled:
OWON SDS7102V (new ver) problems with EXISTING features and hardware
I've brought several of them up in two other threads, but got zero feedback from the resident "pro-Owen" peanut gallery.

[saturation]

Sorry to hear.  On reading you posts here:

https://www.eevblog.com/forum/general-chat/choosing-first-oscilloscope-rigol-noise/msg107370/#msg107370

If the stars be right, features and hardware on Owon and Hantek appear superior to the Rigol, but the quality control and bugs of these 2 scopes increase the risk of some new bugs in updates or unresolved bugs in past firmware, as you later found.

The Rigol is not sexy today, but it does work closer to the published spec sheets released by Rigol than the competing Hantek and Owon scopes, so I would have gotten it instead.

OT:
While running through the FG tests, I came upon a few things that bothered me about THE SCOPE (!).
I think a new thread may be in order titled:
OWON SDS7102V (new ver) problems with EXISTING features and hardware
I've brought several of them up in two other threads, but got zero feedback from the resident "pro-Owen" peanut gallery.

[Bored@Work]

The only main issue I have with it is quality of the generated waveforms in terms of frequency stability, amplitude stability and harmonic purity.

In other words, it lacks key features of a signal generator.

[saturation]

One can get a 10 MHz source range from a simple xtal to an atomic clock or even GPS disciplined, each increasing in cost and stability, its just a question of what its purpose is, so I would presume the buyer has an intended purpose limited to this units capabilities.

Since it has a variable signal and generate the 3 common waveforms, it is technically a function generator.   

Its in line with kit FG like the Elenco, and the market its sold to, too.

http://www.ebay.com/itm/1-MHZ-FUNCTION-GENERATOR-KIT-BUILD-IT-AND-SAVE-NEW-/251049214431?pt=BI_Signal_Sources&hash=item3a73b301df 

The only main issue I have with it is quality of the generated waveforms in terms of frequency stability, amplitude stability and harmonic purity.

In other words, it lacks key features of a signal generator.

[george graves]

Boy is that case ugly.  Just sayin'

[pullin-gs]

Boy is that case ugly.  Just sayin'

Indeed.

Side-note:
The scope I used is battery-powered and has also has a USB for dumping wave-forms to a thumbdrive.  I powered the FG off the scope's USB port.
Not being tethered to a power cord sure is convenient for this sort of work.

[Mechatrommer]

Boy is that case ugly.  Just sayin'

this kind of word that can get you easily killed. that case is famous (or look alike) in hunglow calculator product.

[pullin-gs]

Square wave plots with infinity persistence.
10K


50K


100K


200K


500K


1Meg


2Meg


5Meg

[saturation]

Eyeballing the images, that's about 40ns of jitter.  But don't see any suggestion of drift or amplitude variations.

[Mechatrommer]

now i think i do remember someone did teardown this unit and its a fpga based DDS FG. from the picture i believe if implemented properly given enough hardware, eg clock and dac smpling rate, this unit can produce descent 10-50MHz sine.

[cliffyk]

Eyeballing the images, that's about 40ns of jitter.  But don't see any suggestion of drift or amplitude variations.

I agree with the 40ns assessment, and I'd bet that if you opened it up you would find a 25MHz clock:

0.000000040^-1 = 25,000,000

Here is an analysis of the 1MHz output and trigger from a Velleman PCGU1000 DDS that has a 50MHz clock:



You can see the 20ns jitter in the output signal, with the 'scope synch'd to the generator's trigger output.  This is common with FPGA based instruments, as what they are asked to do exceeds their clock by significant levels.


One other comment--that Elenco thing referenced earlier is a real POS.  I got my 10 year-old grandson one for Christmas (that's what he wanted--good kid).  He and I assembled it and found it's output to be pathetic with sine wave THD of 10%+ even after replacing the fixed tuning resistors with 10-turn pots.

It uses an EXAR XR2206 function generator IC rated for use with a 10V to 26V power supply, Elenco powers it with a single 1604 9V "rectangular" battery?  We clipped two batteries "back-to-back" in series and it got a bit better but even after all that it's still only barely good enough for a 10-year old to play around with...

[saturation]

Yes, we've seen this in past devices but most documented in the Hantek DDS3x25 thread on eevblog.

The Elenco can sell to as low as ~< half the price of this topic's UDB FG, so it wouldn't be surprising if it faired even worse.

But I think the Elenco main appeal is a kit, so most of the experience is in building it, then next using it. 

Most folks who do it own their own seem to get more out of it.

http://www.amazon.com/s/ref=bl_sr_hi?_encoding=UTF8&field-brandtextbin=Elenco&node=228013

Beyond defunct Healthkit, kits have rarely exceeded the quality of a preassembled MTE gear.

The UDB can be found as a kit, but most of the hard work is working and done in the DDS module.

Eyeballing the images, that's about 40ns of jitter.  But don't see any suggestion of drift or amplitude variations.

I agree with the 40ns assessment, and I'd bet that if you opened it up you would find a 25MHz clock:

0.000000040^-1 = 25,000,000

Here is an analysis of the 1MHz output and trigger from a Velleman PCGU1000 DDS that has a 50MHz clock:
...

One other comment--that Elenco thing referenced earlier is a real POS.  I got my 10 year-old grandson one for Christmas (that's what he wanted--good kid). 

[pullin-gs]

Regarding the jitter....
It is an odd behavior: The waveform looks solid for a few 1/10ths of a second, and then shifts over and stays put for another random amount of time from zero to a few 10nths of a second, and then shifts back.  This is repeated over and over.
Important note: The waveform is not filled in between the left-most and right-most shifted waveform.  It is all-or-none.
Note: The exact same behavior is seen on triangle and saw wave forms.
Note: Sine waves look great all the way up to 5Mhz.  I'll post some pics if you want.

[poorchava]

Hm, I know that in fpga's people generally store lookup table with quarter of the sine wave and then cycle up/down and add '+' or '-'. If this is coded poorly, then maybe every X cycles the table counter saturates and the logic needs another cycle to reset it. I believe it can be avoided pretty easily in programmable logic chips, but I guess something like that would actually explain the jitter every XYZ cycles.

Maybe someone has a scope sophisticated enough to check if this occurs at constant intervals and if these intervals are some power of 2. This would prove problem with phase accumulator roll-over.

[pullin-gs]

Maybe someone has a scope sophisticated enough to check if this occurs at constant intervals and if these intervals are some power of 2. This would prove problem with phase accumulator roll-over.

The data to determine this is already captured in the original post.
Yes.....interval is 2-cubed.
Look at any of the traces where "jitter" (I dont think jitter is the correct term for this problem) is displayed. 
Note I am displaying 8 cycles.  Look at the middle waveform, inside leg on the  upswing....it is ALWAYS flat there, the seven remaining wave plots bounce around.   It repeats every 8 wave cycles.

[pickle9000]

Arrgh, So close but yet not quite there.

So I ordered one of these things, yes it works, but.

- Out of the box one of the tactile switches was not properly seated so had to be resoldered.
- The interface works very well, I had trouble reading the manual but the actual unit is very easy to navigate and set. Screen update is very good so no complaints there.
- It can save signal frequency and shape, I really wanted this feature.
- The box is crap on a shelf but for my application (it will be used as part of a permanent burn in jig) it's actually good. The quality of the plastic and overlays is very poor.
-  As far as it being a function generator I'd say only just. Basically I don't trust it. As part of a burn in rig OK, it's cheap and easy to set that's a plus. As for anything else, it's a fail.
- Always use an isolated power supply to power it, not mains isolated.
- The signal is a little twitchy (as noted in the previous posts). In my case it's not an issue but not cool for a signal gen.

I can't really recommend it, it works but with a little more effort it would have been really handy. I also hate to say it but if it turns out to be reliable, I'll probably use it again. It's cheap and easy to set.

...mike

[cliffyk]

With my advanced years I have come to realise that more often than not, "When you buy the cheapest there is, there is a very good possibility you will obtain the cheapest there is." 

It is a sort of corollary to Spock's "After a time, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical, but it is often true."

[Salas]

Square wave plots with infinity persistence.

1Meg

They must have added some filtering meantime because when I had got one like that last year it had so much sqw ringing (beyond the jitter issues) that I sent it back.