Programming AD9850 & AD9851 DDS

🔘I previously posted about using the AD9850 & AD9851 DDS chip evaluation modules in 2018 and again in 2023. To recap, before these devices can be used as a signal source they require programming with 5 bytes of data related to frequency and phase, which form a 'tuning word'.

A µ-controller and a smart phone🖁 App could be used to upload 🠝 the tuning word ( see 16 July 2023 ), or a USB dongle and pc💻 interface software, ( see 4 January 2018 ).  As I have recently updated that software it would now be a good time to give a description.

My dedicated pc 💻 software, called "DdsModTerm", is the user interface which I started developing in about 2015. Since then I have updated it 15 times; the latest revision appearing this month.

DdsModTerm user window

The clock 🕰 frequency and the required output frequency ∿ & phase are entered either manually or by recall from memory. By clicking 'Confirm' the software generates the 5 configuration bytes required from the user input data. In the example in the image above the output frequency is 137700Hz* & bytes hex 00C88AC604. The pc 💻 is connected to the serial data interface of the DDS module via a COM port and a USB-SPI protocol converter dongle.

(L) USB-SPI dongle (R) AD9851 DDS module on adaptor

Clicking 'Update DDS' then uploads the bytes to the registers of the DDS chip using SPI and a voltage having an amplitude 1V peak to peak at the programmed frequency ∿ is then present on the output.

DDS output signal, 1Vp-p, 137.7KHz

Other features of the software include up/down step 🪜tuning, slider tuning control, view of 255 byte eeprom addresses E0-FF, 3 memories for storing frequency, saving custom clock🕓, alias frequencies calculated, and general purpose output ( GPO ) toggling on/off.

The dongle and software are available from me. Post a comment to receive more information. Note that both AD9850 & AD9851 DDS devices are supported.🔘

( Click on images to enlarge detail. )

* 137.7KHz is a calling frequency on the radio amateur 2190m long-wave band, 135.7-137.8KHz.

SPI = Serial Peripheral Interface, 3-wire bus.

AD9850, AD9851 : 🔗Analog Devices Inc. parts, 32-bit CMOS Direct Digital Synthesiser (DDS) chips.

Analog Devices AD9850 frequency synthesiser

AD9850 evaluation board, 45mm x 26mm

Connected to MYDEV2 PIC MSSP module for programming

SINA and QP outputs

Another visit to an online auction site and another electronics purchase. This time I spent $9 on an evaluation board for the AD9850 frequency synthesiser chip. Surely the 125MHz 'can' oscillator and the chip itself are individually worth more than that. However it was made in China.
I mounted it on a larger piece of experimenter board and connected its programming inputs to a microcontroller PIC18F4550 on my MYDEV2 PIC development board. Before the AD9850 will produce an output signal it has to be programmed.
So I wrote a few lines of code to use the PIC's Master Synchronous Serial Peripheral ,( MSSP ), interface module to send the 40 bits of frequency, phase and control data to the AD9850.
The resultant output signals are a sine wave ( CH1 yellow trace ) of 1.04V peak-peak directly from the chip's digital-analogue convertor, ( DAC ), and a variable pulse-width square wave ( CH2 blue trace ) of 5V peak-peak via the chip's comparator for use as an external clock.
I have intentionally allowed plenty of space on the experimenter board to fit a dedicated PIC later; probably the PIC18F14K22 as I already have one.
The AD9850 will be a useful signal source and clock generator upto about 40MHz.

Densely populated

A new batch of Analog Devices synthesiser chips has arrived, enabling me to finish populating one circuit board with components. I programmed the PIC MCU via the bootloader with my latest v2.00 code and, after powering up the board, all seems to be working fine.

SMD soldering success

I have used the tools and materials described in my posting on 20th August to solder successfully in place the frequency synthesiser chip, ( encircled in the picture ); an amazing result, considering it was the first SMT component I had ever attempted to solder, ( since being properly equipped ), and I had only 'perfected' my technique on a scrap piece of circuit board a few moments earlier !
The chip is Analog Devices Inc. 50MHz CMOS complete direct digital synthesiser type AD9835 which measures 5.1mm x 4.5mm and has 8 connection pins on each of the two longer sides to be soldered.
The mixture of 'through hole mounted' components and SMD on the same board is convenient and acceptable for prototyping. With this first SMD soldering success behind me I shall, in time, convert the circuit board completely to SMT in a future version.
Now let me see if the code I have written, ( see 17th May ), to control the chip will actually get it to do what I want.