AD9850 DDS module

[akis]

I have got a bunch of these modules on ebay from different suppliers. I have noticed that a few do not work properly, from the ones I have tested. What happens is sometimes they produce a nice sine wave output at the desired frequency, and sometimes they do not. Flicking the Vcc line sometimes fixes the problem (if you can call that a fix). To explain further, when I flick the Vcc line, the AD9850 module does not power down completely as it is being kept half-powered by the 4 wires connecting it to the Arduino board. But it seems doing this "nudges" something and then the AD9850 starts, even though the Arduino was doing nothing at the time, which further means that the frequency was already transmitted properly but the AD9850 was refusing to produce it, until I flicked the Vcc line.

If anyone has any ideas please let me know.

Many thanks.

[c4757p]

Are you twiddling the reset line on startup?

[akis]

Only when I program it as part of the programming code. But when I flick the Vcc line, the programming has already been done.

Anyway out of 6 modules, 4 work OK, and 2 are funny like that. For my luck, picking randomly out of the box I soldered the one that is funny... I have replaced it now with one that works.

My small worry is that maybe I am doing something wrong and the ones that work only do so out of fluke.

[dannyf]

I have used maybe 10 of such modules. No problem whatsoever.

maybe I am doing something wrong

Maybe. or even likely.

[Rigby]

Seems more likely to me that he's doing things right, or right enough, but that there are some counterfeit or maybe "overused" parts that found their way to him.

Check the data sheet and make sure you're within tolerances everywhere.  If you are, then you have bad parts.  Bad meaning counterfeit, used and broken, or parts rejected in QA.

[Rasz]

start by measuring voltage
when it works, when it doesnt, and when you do your secret flick