I would like to have external DAC to LimeSDR USB/mini. It seems that it is not easy to use GPIO header for SPI/I2C interface. Can I get somehow SPI/I2C interface for external DAC?
I’m guessing you’d need to modify the FPGA gateware. Something similar-ish was done for the larger LimeSDR-USB board — albeit to give SPI access to the LMS7002M from a micrcontroller attached via GPIO.
@Zack could likely advise.
Why is that?
Of course. Just have to change FPGA gateware by assigning GPIO pins for SPI/I2C and updating NIOS system. Although FPGA skills required.
I don’t have much FPGA experience, so that is the reason, why I would not like to modify FPGA gateware. I just wonder if someone has done that already.
What DAC? Do you need to control it all the time or just set some level at some point and forget?
Model is not defined, but I would need two adjustable bias voltages. No need for high speed control. Few times per second would be enough.
Let me know your desired DAC and how you want to connect it to GPIO. Then I can help you with FPGA/SW side at my free time. Do not promise it to be quick although.
For example MCP4822 would meet my requirements. It has SPI interface, which is probably easier than I2C. Basically I would SCK and SDI signals and then CS and LDAC signals can be probably controlled as current GPIO implementation.