Zero crossing detection. parallel inputs to USRP

Hello,

I have once post this message. Please help me cause its very urgent.

I now have a project with the following specifications:
I need to send 2 input-signals parallel over USRP, then find out the
zero-crossings (time) of each signal so I can calculate the phase
difference
of them.
The 1st signal S1 is up to 1MHz
The 2st signal S2 is about 50 Hz

  1. Sending 2 input signals parallel to USRP:
    My idea is:

    • Sending these 2 Signals in 2 separate daughter-boards LFRX
    • (Or) Put them two on only one LFRX through the 2 SMA connectors.
    • How about using digital I/O pins ?
    • What is the maximum voltage can I feed the daughter-board through
      SMA ?
    • Will the inputs be synchronously sent and sampled ?
  2. Zero-crossings detection:

    • How can I find out the zero-crossing time, esp. of the signal S2 ?

Thanks in advance for your reply.

Phong


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Sent from the GnuRadio mailing list archive at Nabble.com.

On Mon, Aug 09, 2010 at 04:42:58AM -0700, Phong Do wrote:

Hello,

I have once post this message. Please help me cause its very urgent.

Generally when there’s no response, it’s an indication that the way
you asked your questions failed to attract the attention of people who
could help.
Try following the suggestions in here:

http://gnuradio.org/redmine/wiki/gnuradio/ReportingErrors

I now have a project with the following specifications:
I need to send 2 input-signals parallel over USRP, then find out the
zero-crossings (time) of each signal so I can calculate the phase difference
of them.
The 1st signal S1 is up to 1MHz
The 2st signal S2 is about 50 Hz

  1. Sending 2 input signals parallel to USRP:
    My idea is:
    • Sending these 2 Signals in 2 separate daughter-boards LFRX

That could work.

  • (Or) Put them two on only one LFRX through the 2 SMA connectors.

That could work too.

  • How about using digital I/O pins ?

Not recommended.

  • What is the maximum voltage can I feed the daughter-board through SMA ?

I’m not sure.

  • Will the inputs be synchronously sent and sampled ?

Yes.

  1. Zero-crossings detection:
    • How can I find out the zero-crossing time, esp. of the signal S2 ?

What have you tried so far?

Eric

  • What is the maximum voltage can I feed the daughter-board through SMA ?

Roughly 0dBm would be a safe bet.

Which translates to roughly 0.22V

There are several handy places on the web for doing conversions between
dBm and voltage:

http://www.raltron.com/cust/tools/voltage_to_dbm.asp

To pick one at random.

Assume 50 ohms impedance for all the daughtercards

In RF system design, it’s usual to talk in terms of power levels rather
than voltages. What you’ll
generally find is that for RF componentry, maximum input levels are
generally quoted in
dBm (dB referenced to 1 milliwatt), and sometimes dbuV (dB referenced
to 1 microvolt).


Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

  • What is the maximum voltage can I feed the daughter-board through SMA
    ?

Roughly 0dBm would be a safe bet.

Which translates to roughly 0.22V

There are several handy places on the web for doing conversions between
dBm and voltage:

http://www.raltron.com/cust/tools/voltage_to_dbm.asp

To pick one at random.

Assume 50 ohms impedance for all the daughtercards

In RF system design, it’s usual to talk in terms of power levels rather
than voltages. What you’ll
generally find is that for RF componentry, maximum input levels are
generally quoted in
dBm (dB referenced to 1 milliwatt), and sometimes dbuV (dB referenced
to 1 microvolt).


Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org

Hello,

thank you for your reply.

I found this information in the forum, I think it is from Josh
“Input Full Scale on LFRX: +10dBm = 2Vpp = 1 Vpeak = 0.7 Vrms”
So I think I can feed the max voltage up to 2Vpp in LFRX, is this right
?

I want to know the max voltage just to be sure I will not kill the LFRX.
The
more important thing is I want to feed the USRP exactly the frequency
(about
50Hz) of the line (home) voltage ( 50 Hz, 230V in europe). Afterthat I
want
to measure this frequency.

  • Do you have any ideas how can I transform the line voltage in lower
    voltage of 2Vpp and get the same frequency out ?
    I think about schmitt trigger or comparator circuit can help. Do you
    know
    some tutorial about this ?

  • To measure the frequency comes USRP, I write a new block using
    zero-crossing algorithm (base on howto-write-new-block). Please have a
    look
    in my cpp code if it is wrong.


float zero[];
int k;

for (int i = 0; i < noutput_items; i++){
if (in[i] = 0){
zero[k] = i;
k++;
}
}
out = 2*(zero[k]-zero[k-1]);

// Tell runtime system how many output items we produced.
return noutput_items;

http://old.nabble.com/file/p29415484/howto_frequency_ff.cc
howto_frequency_ff.cc
http://old.nabble.com/file/p29415484/howto_frequency_ff.h
howto_frequency_ff.h
http://old.nabble.com/file/p29415484/howto_frequency_ff.i
howto_frequency_ff.i

I appreciate your help.
Phong


View this message in context:
http://old.nabble.com/zero-crossing-detection.-parallel-inputs-to-USRP-tp29386998p29415484.html
Sent from the GnuRadio mailing list archive at Nabble.com.

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