Finally, some updates on the AVR DDS3 signal generator. The 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. The second Atmega88 is gonna be used for signal generators only. This will give un-interruptable signal output while changing parameters or simply doing signal sweeps.
A simple keypad should be convenient for entering frequency values and menu navigation.
Maybe this isn’t the best choice, but this is what I had on a desk and wanted to put it to use. If I find it annoying and there will be more bugs or more flaws, the schematic will be remade.
I decided to add a computer interface. So there is a UART connector that suits SparkFun’s FTDI Basic Breakout board.
There is not much change in the DDS generator since the last projects. There is the same R2R resistor ladder DAC used, which is a simple and cheap solution. I have used the Atmega88 microcontroller here, which has 8KB of Flash, 1KB of SRAM.
I haven’t decided yet, but all signal data will probably be stored inside the controller chip and uploaded to DDS microcontroller SRAM using the SPI interface. This will be easier to upload new signals using a PC. And finally analog part. This is the same circuit that was modeled in this previous post.