[sdiy] Optoisolated USB ?

[Seb Francis]

Hi,

I've run into an unfortunate problem using a Microchip ICD2.  When I 
connect it to a PIC circuit on my breadboard I'm getting fairly loud 
digital-type noises coming from my PC sound card.  This seems to be 
because the ICD2 is connected to the mains earth of the PC via the USB 
connection and at the other end the breadboard is connected to a 
different mains earth via my oscilloscope ground.  If I disconnect the 
scope ground then the noises stop.  If I connect the scope input to the 
breadboard ground I can view the potential difference between the 2 
grounds - I'm seeing plenty of digital noise and glitches, sometimes as 
high as 2V ptp.  Even if I can live with the digital noise while using 
the ICD2, this kind of mains-connected interference seems a bit risky 
for my equipment.

I haven't tried connecting the scope to the same mains outlet as the PC 
(don't have a long power lead right now), but I'd prefer a more isolated 
solution to this.

It seems like I have 2 options:

(1) Disconnect the scope's ground from mains ground
Is this a bad idea?

(2) Buy/make an optoisolated USB hub.
The only one I've found costs $280 !
Can't be that hard to make one?  Anyone have any info how to make a 
quick&easy one?

Or is there some solution I've missed?

TIA,
Seb