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: discuss-gnuradio-bounces+evan=syndetix....@gnu.org
[mailto:discuss-gnuradio-bounces+evan=syndetix....@gnu.org] 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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