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

[Evan Merewether]

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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