Re: [Discuss-gnuradio] discussion on USRP-->Wall Socket for Power Line Comms

[John Ackermann N8UR]

Well, I'd put it that large resistors result in high impedance.  You 
still have the full line voltage across the output of the two resistors, 
but any load resistance will form a voltage divider and drop the voltage 
very quickly.

A simple next step would be adding an appropriate load resistor and 
using an op-amp as a follower to provide a low impedance output to drive 
the BasicRX.

I'm not sure why you'd need to unground anything -- the output is an AC 
signal, and the resistors limit any current to a miniscule and safe 
level.  Folks have been plugging this design into all sorts of grounded 
gear with no issues at all.

John
----
On 2/21/2012 3:57 PM, Evan Merewether wrote:
> Two issues:
> 1) Large resistors results in large attenuation.  This circuit attenuates
> 120VAC to ~5V for the microcontroller.
> 2) You would need to un-ground all of the components (USRP + PC + you) and
> float everything to somewhere around 60V
>
> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf Of
> John Ackermann N8UR
> Sent: Tuesday, February 21, 2012 1:45 PM
> To: George Nychis
> Cc: discuss-gnuradio
> Subject: Re: [Discuss-gnuradio] discussion on USRP-->Wall Socket for Power
> Line Comms
>
> On 2/21/2012 3:00 PM, George Nychis wrote:
> > Okay!  So apparently there is some interest in power line communication
> > for GSoC.  But, what we would want to do is already have a safe way of
> > connecting the USRP in to the wall socket for the student(s), and for
> > the future of GNU Radio and USRP power line communications development.
> >
> > So, as a goal of this thread I'd like to get some feedback on how we can
> > make this possible.  Ideally, something off-the-shelf would be great,
> > providing the highest amount of safety for those experimenting with it.
>
> Here's a very simple approach:
>
> http://leapsecond.com/pages/ac-detect/
>
> There was a bunch of discussion about this on the time-nuts mailing
> list, and some folks suggested changes for increased safety (including
> putting two resistors in series so that if one fails short -- which is a
> very unusual occurrence -- there's an extra layer of protection.  But in
> general, with large value resistors the current is limited to a very
> safe level -- and it's current that kills, not voltage.
>
> John
>
>
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