Generic AD9850 DDS Modules: Beware Swapped D7 and GND Pins!

Compare this picture:

AD9850 DDS Module - swapped GND D7 pins

AD9850 DDS Module – swapped GND D7 pins

… with any of the doc for the generic AD8950/51 DDS modules you’ll find out on the Interwebs. This snippet from the seller’s schematic will suffice:

AD9850 module schematic - cropped

AD9850 module schematic – cropped

Here’s a closer look at the 2×7 header in the upper left corner:


AD9850 module schematic - J5 detail

AD9850 module schematic – J5 detail

Don’t blame me for the blur, the schematic is a JPG.

Compared it with the board in hand:

AD9850 DDS Module - swapped GND D7 pins - detail

AD9850 DDS Module – swapped GND D7 pins – detail

Yup, the D7 and GND pins are reversed.

Some careful probing showed the silkscreen is correct: the pins are, in fact, correctly labeled.

Should you be laying out a PCB in the expectation of using any DDS module from the lowest-price supplier, remember this high truth: Hell hath no fury like that of an unjustified assumption.

Fortunately, I’m hand-wiring the circuit and caught it prior to the smoke test.

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  1. #1 by Vedran on 2017-05-18 - 13:05

    I’m sure the good people of China gave you the correct schematic, it’s just that you’re not using the correct package for the J5 part – it’s the rare 1×7 pin header with swapped 6 and 7 pins :)

    • #2 by Ed on 2017-05-18 - 13:34

      Well played, sir!

  2. #3 by celem on 2017-05-21 - 08:20

    Wow – that’s a pretty nasty flaw. Was it an eBay purcbase direct from China?

    • #4 by Ed on 2017-05-21 - 09:39

      Turns out I paid a bit more to get them direct from New York City, although there’s not a trace of doubt in my mind concerning their actual origin.

      I now see a newer (?) layout with the parallel input pins lined up on one header and everything else on another, at a price 3 dB down from previous levels. It must be better!

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