Day: May 18, 2017

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.