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AD9850 Frequency Generator BoosterPack

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This project uses an inexpensive AD9850 board obtained off eBay to create a frequency generator boosterpack that is especially useful with the MSP-EXP430FR6989 LaunchPad. It features an encoder with a pushbutton to adjust frequency. In the photo below it is generating a 7000 Hz signal which agrees nicely with the oscilloscope.


The schematic is simple:


The encoder is a Bourns 652-PEC12R-4225F-S24. I tried various arrangements and value of resistors and capacitors for debouncing the encoder and switch. In the end I just added some capacitance as shown in the schematic. On the oscilloscope it looked pretty clean so I called it good enough. All the parts are through hole as seen in the photograph below:


The fit is tight but fortunately all the materials were on hand when the PCB was being designed so I printed out a paper PCB outline and checked it before ordering.


If I were making it again I would increase the size of the board a bit to allow larger/additional labels. Otherwise, everything works and it turned out fine. This is a picture of the unpopulated boards I received from Osh Park.


While it should work with most LaunchPads I had the FR6989 in mind as I developed it - in particular I wanted to use the integrated LCD display. Accordingly, I was careful not to obscure the display or the reset button. The software was developed with Energia V17. Here is a photo of what it looks like in operation:


The output from the AD9850 comes out the jumpers attached to the 90 degree male header pins marked with arrow A. The dark jumper wire is GND and the sine wave is coming out of the lighter wire on the right. Adjustments are made with the encoder knob marked by arrow B. Turning it adjusts the frequency up and down and the current value is output on the LCD as shown by the arrow C. The range is from zero to 32 MHz. Since fine adjustment is desired, as well as rapid adjustment, the push button on the encoder is used to change the coarseness of the adjustment. The magnitude is indicated by the battery indicator on the LCD as shown by arrow D. For example, in the photo three battery bars are showing which indicates that each adjustment/click of the encoder will change the output by 1000 Hz. When the encoder is pushed down it will cycle through in this case to 100 Hz adjustment (with two bars showing), 10 Hz (one bar), 1 Hz (no bars), and then up to 1 MHz (six bars), and so on. In practice, it adjusts pretty quickly with good resolution.


One enhancement might be to have the software scroll the output value since as is it won't display full resolution due to the 6 digit screen. The Energia sketch can be found here.


I have an extra PCB so if you are active in the 43oh forums and would like it then send me a personal message and I will mail it gratis.

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Hi @@yosh - I went ahead and shared it on OSH Park under the title AD9850. There is one unusual thing about the rendering of the top layer of the PCB on the OSH Park site.  The footprint of the AD9850 as I drew it in KiCad extends beyond the actual PCB and OSH Park's display software picks up the whole thing even though the size (and cost) of the PCB is smaller. The actual size is as shown in my photographs above.  The bottom layer as shown at OSH Park is correct.


One other thing I thought I would mention.  When designing the board I thought the tabs on the encoder that can be used to snap it in place might cause an interference problem so I didn't make slots for them in the board.  Accordingly, you must pinch them off before soldering the encoder.

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