On Jul 28, 3:59 am, "G \"Guglielmo\" Evans G4SDW"
wrote:
Does anyone have experience and/or recommendations
for analogue and digital I/O interfaces based on the Universal
Serial Bus (USB)?

Just an idea for the genesis of a homebrew spectrum analyser.

Ive done a little with USB, so I'll add a little background if not
provide complete answers.

The first hurdle is the interfacing. You need a board with a driver
thats easy to interface with your host PC software program.
Ive used a board from www.mirrorbow.com for general control...you can
access it every 1mS and get 12 x 12bit ADC samples for each access, or
you can alter 8 bit digital ports etc. However, the speed is limited
to how fast the operating system can access the board, which is 1mS.
This board pretends to be a com port so it makes programming easier
without needing to include libraries and dlls etc.
Theres a board from National Instruments which I think is faster,
though only around 2.8Msamples/sec http://sine.ni.com/nips/cds/view/p/lang/en/nid/202596
And of course there are some dedicated USB spectrum analyser
available, but thats not the same as doing a home version.
So, you could just get a DAC board and go for it, though the speed you
can make a spectrum analyser is limited.

Of course you could use the superhet principle with a narrow band
filter and a programmable LO. You could then use a simple IO board
like the one from Mirrorbow to setup the LO, then use a peak detector
and the boards AD to give an indication of level. You'd then have a
digitally controlled analogue spectrum analyser, and you woudlnt need
the large sample rate.