Test Equipment: Oscillocopes

[MileHigh]

Brian:

I only know very little about what's out there.

The software tools, feature set of the board and price are your three main considerations.  That board looks like an FPGA along with a CPU.  That's pretty amazing but you don't need the FPGA.  I am not sure what hardware and software features you want.  Then just shop around to find a board with all or most of your features.  The brand or the architecture of the CPU are really irrelevant here.  Jut get something mainstream.  This app requires no real processing power.

I am pretty sure the SPI interface can be done with a few I/O pins and a readily available library, you should check that.  It looks like writing your own SPI interface driver would be pretty easy also but it has to exist already.

MileHigh

[MileHigh]

Here is an interesting Plan B:

You don't even buy a microcontroller board.   You do all of the software for the frequency generator register poking and the GUI on your PC and you get a USB to SPI dongle.

http://www.cypress.com/?rID=57207

Then the external box just has the waveform generator chip, the power supplies, and the support electronics, etc.

[MarkE]

Here is an interesting Plan B:

You don't even buy a microcontroller board.   You do all of the software for the frequency generator register poking and the GUI on your PC and you get a USB to SPI dongle.

http://www.cypress.com/?rID=57207

Then the external box just has the waveform generator chip, the power supplies, and the support electronics, etc.

First the development board that Brian found is for an FPGA.  There is not a hardware uC on board.  Any uC would be soft in the modest sized FPGA.  A uC is useful for things like a front panel display.  So the USB to I²C dongle is a better way to go.  If there were enough interest we could kick around an open source design for a USB based function generator with really nice capability, like +/-20Vpp output drive.

[Brian516]

MileHigh:

I know that I won't need an FPGA for the function gen project, but I was just thinking that might be a nice to have dev board for a large variety of projects.  But now that I'm fully rested and awake, I think I would likely dedicate whatever is used to the FG, so you're right, it's pretty pointless to get for this project.  Maybe later on down the road when/if I find something I would need the FPGA for.  Plus I see now that it doesn't have I2C or SPI, either.

I don't see a price for the DG USB to SPI/I2C dongle on that page. Maybe one has to contact them to find out.. It's obv from Germany so maybe shipping would be more then the device itself, but still should be fairly cheap anyway.  Either way, it would be a great tool to have.

I was poking around the other day and found a schematic and instructions for building an easy USB to I2C dongle that I'm sure could be adapted for SPI.  I couldn't find the link right off hand, but I'm pretty sure I saved the page in a folder and will find and add it once I do.

Speaking of PC based, Check this out:
http://hackaday.com/2014/10/22/function-generator-with-zero-cpu-cycles/

It says it was only used for 200khz, but maybe there is a similar chip to the PIC32 that can get us to the Mhz range?  They don't really give enough info on it so I'll have to dig around for more info.    Chances are, this is specifically around the PIC32 chip and doesn't work with any that will get us in the Mhz range, but it's an interesting article/idea anyway.  Good to know about if someone ever needs a quick, clean sine wave up to 200khz if nothing else.

I don't know if it was just my PC/connection, but for most of the day yesterday this site was almost completely unavailable as if there were some major server issues. Anyone else have that problem?  If not I'm going to have to do some PC cleaning........  I need to put a partition on here and put Linux on it anyway.

Brian

[MarkE]

The PIC scheme is a poor match to a DDS chip.  The PIC scheme can only output values at integer divisions of the DMA clock.  DDS performs M/N*F_CLOCK frequency synthesis.   Up to the resolution of the internal numeric represetnations, you can get pretty much any frequency that you want.