Amateur Radio, Electronics Workbench, Oddities

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.

5 thoughts on “Generic AD9850 DDS Modules: Beware Swapped D7 and GND Pins!”

  1. 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 :)

    1. 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!

  3. Pingback: Generic I²C 128×64 OLED Displays: Beware Swapped VCC and GND | The Smell of Molten Projects in the Morning

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