Finally some update on AVR DDS3 signal generator. Circuit is practically done and PCBs are made. I decided to go with two microcontrollers on board to make it more functional. One microcontroller Atmega328P is gonna be dedicated to user interface and signal generator control. Second Atmega88 is gonna be used for signal generator only. This will give un-interruptable signal output while changing parameters or simply doing signal sweeps.
Simple keypad should be convenient for entering frequency values and menu navigation.
Maybe this isn’t best choice but this is what I had on a desk and wanted to put in to use. If I find it annoying and there will be more bugs or more flaws schematic will be remade.
Decided to add computer interface. So there is an UART connector that suits SparkFuns FTDI Basic Breakout board.
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There is not much change in DDS generator since last projects. There is the same R2R resistor ladder DAC used which is simple and cheap solution. I have used Atmega88 microcontroller here which has 8KB of Flash, 1KB of SRAM.
Haven’t decided yet, but probably all signal data will be stored inside controller chip and will be uploaded to DDS microcontroller SRAM using SPI interface. This will be easier to upload new signals using PC. And finally analog part. This is same circuit that was modeled in this previous post.
Here are eagle layouts and PCB images of AVR DDS3 generator:
Next step is gonna be soldering and doing simple tests to make sure everything works as modeled. Stay tuned.