Using AD9835 DDS chip with BASIC-52

Posted on Feb 5, 2014

AD9835 is a DDS (direct digital synthesis) chip from Analog Devices. It contains a phase accumulator, sinewave table, and 10-bit D/A converter. In can be used for phase and frequency modulation by selecting the phase and frequency of the signal either under software control, or using I/O pins (4 phases, 2 frequencies). Although the chip is designe

Using AD9835 DDS chip with BASIC-52
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d for RF applications, it makes a good audio frequency sinewave generator, too. The schematics below shows how to hook it up to 8052-BASIC chip. The circuit is quite straightforward. MCU clock is used as master clock for DDS, control interface is connected to PWM_OUT, T2EX, and T2. Phase and frequency selector pins are not used in this application, so they are tied to ground. Resistor and capacitor values are straight out of a datasheet schematics. Do filter the AVDD power supply, and keep the analog and digital grounds separated, connect them in single point as close to power supply as possible. The output voltage that is developed on R1 is between ground and REFIN (about 1. 2V with internal reference used by connecting REFOUT to REFIN). AD9835 comes in TTSOP-16 package (0. 65mm pin spacing), and only that. You probably need some magnifying equipment to work with it (depending on your eyesight and steadiness of your hand). I just scanned the result with flatbed scanner at 1200dpi and examined the result. In general, the best option for prototyping in my opinion is a `format conversion`. This is how I usually do it. I soldered the DIP-24 socket on veroboard, then cut a suitable size piece of a board and placed it over the socket. I then stuck a wire into socket through the board, soldered and trimmed the wire. The end result is a crude DIP-24 package. I then scraped the pads off from where the TTSOP case needed to go, and...

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