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

[Evan Merewether]

-----Original Message-----
From: Evan Merewether [mailto:address@hidden 
Sent: Tuesday, February 21, 2012 2:29 PM
To: 'John Ackermann N8UR'
Subject: RE: [Discuss-gnuradio] discussion on USRP-->Wall Socket for Power
Line Comms

May I suggest looking at the schematic at the bottom of page 4 of
http://www.belfuse.com/Data/Datasheets/0557-7700-xx-INT5500.pdf

This circuit will provide exactly what you want with reasonable signal
attenuation and provided isolation for safety. 

-----Original Message-----
From: John Ackermann N8UR [mailto:address@hidden 
Sent: Tuesday, February 21, 2012 2:13 PM
To: Evan Merewether
Cc: 'George Nychis'; 'discuss-gnuradio'
Subject: Re: [Discuss-gnuradio] discussion on USRP-->Wall Socket for Power
Line Comms

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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