Wednesday, 20 January 2016

Done (Mostly)

So there is one wrinkle in my System One interface card: the auto-detect doesn't work for some reason.  I'm pretty sure the logic is all there, and I've tested it with QBasic test programs.  I can start the AP software (S1.EXE) from the command line and specify the interface card address with the /I option and then everything is fine.  So at this moment in time I don't fancy digging in deeper to fix this minor issue.  It doesn't stop me using this amazing machine.

A side note: after setting the SystemOne to internal loopback I measure the THD+N as 0.0014% on both channels.  That's a decent 8dB better than the 8903B (about 0.0035%).


Monday, 18 January 2016

Analyze This!

It works!  The damn thing works!!

Well, okay, there were a few bugs in the Verilog, but checking out each block soon ironed out those.

Ta daaa.... Start up screen:
Eagle-eyed readers will note the flat grey cable poking out the case - that's the ISP download cable for the Lattice CPLD.

A quick graph showing that scans are working (needed the external interrupt line wired up properly - took an evening to fix that little bug):
Note that the performance at the moment (THD+N @ 0.0033%) is about on par with the 8903B it currently sits on top of:
But that's with a less-than-ideal coax cable - I can shift the TND+N over 0.01% just by handling the cable.  I think I really need to look into replacing those BNCs with proper Neutrik XLRs.

The PC that I am using is an Advantech industrial control PC in a small case.  It has a 486 processor running DOS 5.00.

For now, this is just what I need.  Perfick!