AD9850 Module and DDS3x25 DDS based FG Compared

[Mechatrommer]

finally i managed to make my standalone FG based on the AD9850 i bought from ebay. roughly its functional, FW and UI (housing) refinement will follow. not much to say except... i'm very happy with the result. AD9850 Module is really bang per buck even when compared to the more robust and expensive DDS3x25.

pros:
- 1/30x to 1/10x the 3x25 cost (depending your additional circuit setup)
- easily made standalone using simple mcu (atTiny13A is used in this case)
- TTL level square wave (double the 3x25 synch out)
- can be used as PWM generator since the square output is from the chip's comparator with external trimpot level adjust

cons:
- only 1Vpp sine out if without additional amplifier and biasing circuit.
- distortion (as claimed) at higher frequency (20-50MHz) but for high speed application which doesnt care signal purity or for digital clocking, not an issue.
- spike at the rising or falling edge of the square signal (may result false trigger), not sure if its from my poor pcb layout or internal of the AD9850.


this is where i bought it from... http://www.ebay.com.my/itm/New-AD9850-DDS-Signal-Generator-Module-0-40MHz-Test-Equipment-/170783661135?pt=LH_DefaultDomain_0&hash=item27c37fdc4f

without further boring the readers... here the attachment and result showing the produced signal.
CnC welcomed esp for my analog frontend circuit, i think that will be on par with dave's circuit when he was 5 years old, but gladly it more or less works
FWIW.

[casinada]

Nice work I have the other version of the board  and also the Parallel board that connects the AD 9850 to the computer. It works fine but as you mentioned There is no output amplification.
There is a new seller that is offering a little box for a decent price. I don't know if anybody has purchased it.
http://www.ebay.com/itm/AE20125-10-MHz-Sweep-DDS-Function-Generator-Kit-with-USB-and-Modulation-/251169054479?pt=LH_DefaultDomain_0&hash=item3a7ad79f0f
It says made in Germany but I haven't been able to find their web site.

[toli]

How are they able to sell this so cheap (the first post, not the second) when the IC alone costs 3 times as much on digikey?!

[Mechatrommer]

thats a whole new circuit. just the chip is the same. the fact that it can do triangle proved that he probably designed it from scratch and properly since he's limiting it to 10MHz. $70 is not that bad, but its getting closer to dds3x25 price (arbitrary). now digital button vs analog trimpot, i can see some merit to analog trimpot, though we cant get exactly and precisely the frequency we want, but the experience is different, i can already felt it vs my pc controlled dds3x25, i think i'll leave it that way (analog trimpots for all option).

[Mechatrommer]

How are they able to sell this so chip (the first post, not the second) when the IC alone costs 3 times as much on digikey?!

here fun to read ... searching ad9850 in eevblog...

https://www.eevblog.com/forum/general-chat/whats-wrong-with-digikey-ebay-and-the-pricing/
https://www.eevblog.com/forum/projects-designs-and-technical-stuff/too-good-to-be-true-fake-ad9850/
https://www.eevblog.com/forum/beginners/cheap-ad9851-based-signal-generator/

[toli]

Thank you for these links. Very interesting to see. Most times when I see eBay stuff going for 1/3 of the mouser/digikey price I automatically assume its a fake

[poptones]

Nooelec is a very good seller for those in the US, but I doubt the device he's selling for $14.95 isn't just one bought from china for 5 bucks. The upside is not having to wait a month for delivery. Of course the one from china could be junk as well, but you could buy three and if one is bad then use one and sell the other good one.

[Mechatrommer]

Of course the one from china could be junk as well, but you could buy three and if one is bad then use one and sell the other good one.

you can see the result in the 1st post. i only bought one thats what i can put at stake. not sure though what i got is junk or the good one. as other things in the world i guess, we dont expect it to perform better at the edge of its limit. i havent studied the ad9850 yet whether its on spec or not, i dont think i will care. my 2cnts... YMMV.

[Fraser]

I have some PC controlled oscilloscopes so needed a simple PC controlled signal Generator.
I bought this one:

http://www.ebay.co.uk/itm/PC-controlled-20-MHz-Sine-Wave-Generator-Frequency-Counter-/190740349342?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item2c6902c19e

It is a 20Mhz signal generator and a frequency counter. Control software is supplied.

The price I paid was US$42 and its uses the same analogue devices AD9850 mini PCB that apppears in first post on this thread. It actually works very well for the money and is nice and compact  I use a simple analogue output attenuator.

Fraser

[Rerouter]

Mechatrommer would there be any chance of getting a capture of 1Hz or even 0.1Hz, i myself am planning on making a FG out of an AD9850, but will need to use such low frequencies from time to time and am left wondering what the waveforms begin to look like at those speeds (purity doesn't matter to me)

[robrenz]

Nice work Mechatrommer!

[Mechatrommer]

Mechatrommer would there be any chance of getting a capture of 1Hz or even 0.1Hz, i myself am planning on making a FG out of an AD9850, but will need to use such low frequencies from time to time and am left wondering what the waveforms begin to look like at those speeds (purity doesn't matter to me)

since my output amplifier and filter (1µF high pass ac coupled cutoff somewhere < 10-100Hz) are not designed to such low freq, i made a capture directly out of the module's sina pin (sinb can do as well and is filtered probably higher purity but attenuated at high freq). here's the capture with modded software to produce such more precise freq...

1) 1Hz
2) 0.086Hz (thats close to 0.1)
3) 0.029Hz (its lowest resolution/frequency step)
4) 1Hz with the opamp + filter output (attenuated from Vamp setting) FWIW

Nice work Mechatrommer!

sir! thank you sir!

[Rerouter]

thank you very much

[saturation]

Great job mecha!  At least it gives others looking for a FG a low cost alternative that is also partly a kit.

[bingo600]

I got 2 of those boards from ebay.
I fought the first a long time, and couldn't get my AVR software to function.
It turned out that the chinese used a 3v3 125Mhz Osc , wo. any notice.
And i powered the DDS board & AVR with 5v, the Osc was functioning when i initial measured it.
But before i got the AVR software made , the OSC apparently died.
And i blamed my AVR software   

So watch out for the onboard Osc specs.

Besides that it's working fine , i now clock it with a 10Mhz rubidium.
And really need to adjust the output filter on the PCB .....

But you can't get a nice 10Mhz out if clocked by 10Mhz.


/Bingo

[Mechatrommer]

It turned out that the chinese used a 3v3 125Mhz Osc , wo. any notice.

how to check and ensure this in our board? there's no mark. i run my ad9850 with 5V supply, the osc is running hot, but the dds is running ok also the first time i tried to program it, its not working it turned out that reset pin that i left floating need to be hard grounded. probing the osc showing 125MHz oscillation between 1-2v minimum to 3v max iirc. another notes to watch out.

[T4P]

Sure, it's cheaper.
But it's not a ARB func gen. Different game and you know it, mecha and plus 100MHz sine ... with your goltek 

[Mechatrommer]

But it's not a ARB func gen. Different game and you know it, mecha and plus 100MHz sine ... with your goltek 

yes ad9850 will not replace 3x25. each one with their own speciality. ad9850 doesnt rely on PC to operate and very quick (my analog trimpot setup), cheap and wont hurt if it got damaged. 3x25 can be setup to do automated sweep task and PC control, but slow to operate manually. i'll put 3x25 in its safe place while playing with ad9850 in hazardous environment, when there is very specialized task need to be done i'll take out my 3x25. fyi for this whole year i played nothing but sine and square.