[pvrusb2] USB devices and dirty power [was: pvrusb2 Digest, Vol 26, Issue 6]

[Mike Isely]

On Tue, 16 Oct 2007, devsk wrote:

> > What happened,  my wife turned on the light over the foyer.  Turning it
>  on
> > and off will 90% of the time cause the unit to error.
> 
> Legendary stuff!!
> 
> I am glad you got past the problem.
> 
> -devsk

Very amusing.

I've said it before in the past - people don't realize that modern PC 
power supplies can handle a reasonable level of power abuse.  I used to 
experience brownouts here last for the better part of a second while the 
computer just keeps on going without so much as a hiccup - all before I 
ever got a UPS.  PC power supplies have pretty decent energy storage 
capacity to carry then across short glitches and power sags.  But that 
little switcher wall-wart on the end of your USB device's power cable 
doesn't stand a chance in situations like that.  This sort of thing is 
really apparent with externally powered devices that must maintain 
careful synchronization with the host.  Monitors can blink out for a 
second with no ill effects but not a USB device!  So you're left with 
head-scratching situations where the USB device dies but the PC keeps 
going...

Unfortunately this generally means you need to power the USB device from 
a UPS or at least a pretty hefty surge supressor (won't help with 
brownouts but should at least smooth out very short glitches).

My mythtv box here is on its own UPS, and its associated pvrusb2 device 
is also powered from that same UPS.  The box isn't perfect, but at least 
none of the problems ever involve the pvrusb2 device going awol :-)

  -Mike


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