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Re: [Raspberry_Pi_4-Ham_RADIO] WsprryPi

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  • Robert Nickels
    It was probably obvious from my previous comment that I was anxious for the WSPR.NET website to come back up so I could again test my Pi transmitter. But it
    Message 1 of 6 , Apr 5, 2013
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      It was probably obvious from my previous comment that I was anxious for
      the WSPR.NET website to come back up so I could again test my Pi
      transmitter. But it turns out the database was running all along even
      when the website was down, and to my surprise there were over 165 spots
      in the database from the past 15 hours, including several spots from
      France - 6976 km distant! This was all on 20 meters using a homebrew
      LPF connected to the Pi, and feeding a 3 element SteppIR (which was
      pointed at the southeast US). I was hoping that having a good antenna
      would help, but this really blows me away. I turned the beam toward
      Europe about 10 minutes ago and just got a spot from Belgium - around
      the world on a GPIO pin!

      A big thanks to Guido and others who have made this possible and to
      Eddie, Paul, and those who have helped me overcome a few obstacles.
      I'm a believer!

      73, Bob W9RAN
    • Robert Nickels
      Sad news to report ;-( After two days of amazing spots on WRPR it seems my Pi has died while in Wsprry Pi service - although I have no idea whether it was
      Message 2 of 6 , Apr 7, 2013
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        Sad news to report ;-( After two days of amazing spots on WRPR it
        seems my Pi has died while in Wsprry Pi service - although I have no
        idea whether it was KIA or just coincidence.

        I'd switched the antenna to a vertical last night and started the beacon
        around 0445 UT in order to evaluate it's performance against the beam
        I'd been using on 20 meters. This morning I was surprised to only see
        no spots after 12:22 UT, and upon investigation I discovered that the
        beacon had failed and the Pi would not boot up. Upon further
        investigation using a bench power supply, I observed excessive current
        consumption (1.1 A from the 5 V supply) and the output of the 3.3 volt
        regulator is low, and drops even lower the longer power is applied - to
        less than 2 volts. One time I was able to observe a partial boot
        sequence before everything dropped out. The 3.3 volt regulator package
        is hot to the touch after such attempts and the 3.3 V line measures < 2
        ohms to ground. Fried Pi!

        My theory is that some part of the SOC has been damaged, and while the
        CPU part is still intact (and tries to run), the damaged part is
        drawing so much current that the regulator fails to achieve the 3.3 VDC
        needed (or drops below that level very quickly). The polyfuse is
        fine, and was not in the circuit at the time as I was feeding power to
        the Pi via the GPIO connector based on a suggestion I found on one of
        the R-Pi sites to eliminate having to use the microUSB cable. I
        wasn't aware until I looked at the schematic today that this method
        bypasses the fuse, although I'm not sure how that would have made a
        difference in this case.

        For Wsprry use, the low pass filter is capacitively coupled to GPIO pin
        7 (R-Pi) which is connected directly to the GPIO4 (Broadcom) pin on the
        BCM2835. Hindsight being 20/20, I now wonder about the wisdom of
        coupling a outside antenna to a GPIO pin that goes directly to the CPU
        chip without any kind of isolation. Transient voltages such as
        lightning or static buildup as well as RF from other transmitters
        operating into nearby antennas are a concern. And, a ground loop is
        created between the shielded side of the antenna coax and an other
        device connected to the Pi that wind up grounded via the AC powerline
        neutral or grounding conductors. My theory is that the GPIO was
        damaged by one of these means, or in some other way that I haven't
        thought of yet.

        I think that one stage of isolation using a simple BJT amplifier would
        provide cheap insurance, as would galvanic isolation between the antenna
        and the Pi. I plan to try both when the replacement Pi arrives.
        Meanwhile, I thought others could benefit from this experience.

        Any thoughts or theories on this would be appreciated as well,
        especially by Guido and others who have been using Wsprry Pi longer than
        I have.

        73, Bob W9RAN
      • Jim Thisdale
        Couple thoughts: 1 - most wall wart power supplies will NOT provide a GROUND, they can t if they are the simple 2-pin ac plug type since they only use hot and
        Message 3 of 6 , Apr 9, 2013
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          Couple thoughts:

          1 - most wall wart power supplies will NOT provide a GROUND, they can't if they are the simple 2-pin
          ac plug type since they only use hot and neutral. Even if you found a 3-pin one, most likely the DC
          output will be isolated from the AC connector.

          2 - the ethernet connection will not normally supply a ground to the pi either.

          3 - If you want the Pi grounded you are probably best off to supply a good ground to the pi separately.

          4 - If your using the GPIO pins as OUTPUTS some isolation/buffer chips/transistors are highly
          recommended, especially to drive an antenna.

          5 - If using the GPIO pins as inputs, buffering/isolating is almost mandatory, especially since they
          are 3.3v max.

          6 - The micro-usb power connector is the only fused power input. Power applied anywhere else needs
          to be fused externally from the board. (option - modify the board)

          7 - good news, Pi's are in-expensive... Not like frying a $800+ computer.

          -Jim- N1JMM, KB1YPL_B
          Visit my Pi running ircddb, dvrptr, Apache & many other things:
          http://n1jmm.no-ip.org

          On 4/7/13 8:02 PM, Robert Nickels wrote:
          >
          > Sad news to report ;-( After two days of amazing spots on WRPR it
          > seems my Pi has died while in Wsprry Pi service - although I have no
          > idea whether it was KIA or just coincidence.
          >
          > I'd switched the antenna to a vertical last night and started the beacon
          > around 0445 UT in order to evaluate it's performance against the beam
          > I'd been using on 20 meters. This morning I was surprised to only see
          > no spots after 12:22 UT, and upon investigation I discovered that the
          > beacon had failed and the Pi would not boot up. Upon further
          > investigation using a bench power supply, I observed excessive current
          > consumption (1.1 A from the 5 V supply) and the output of the 3.3 volt
          > regulator is low, and drops even lower the longer power is applied - to
          > less than 2 volts. One time I was able to observe a partial boot
          > sequence before everything dropped out. The 3.3 volt regulator package
          > is hot to the touch after such attempts and the 3.3 V line measures < 2
          > ohms to ground. Fried Pi!
          >
          > My theory is that some part of the SOC has been damaged, and while the
          > CPU part is still intact (and tries to run), the damaged part is
          > drawing so much current that the regulator fails to achieve the 3.3 VDC
          > needed (or drops below that level very quickly). The polyfuse is
          > fine, and was not in the circuit at the time as I was feeding power to
          > the Pi via the GPIO connector based on a suggestion I found on one of
          > the R-Pi sites to eliminate having to use the microUSB cable. I
          > wasn't aware until I looked at the schematic today that this method
          > bypasses the fuse, although I'm not sure how that would have made a
          > difference in this case.
          >
          > For Wsprry use, the low pass filter is capacitively coupled to GPIO pin
          > 7 (R-Pi) which is connected directly to the GPIO4 (Broadcom) pin on the
          > BCM2835. Hindsight being 20/20, I now wonder about the wisdom of
          > coupling a outside antenna to a GPIO pin that goes directly to the CPU
          > chip without any kind of isolation. Transient voltages such as
          > lightning or static buildup as well as RF from other transmitters
          > operating into nearby antennas are a concern. And, a ground loop is
          > created between the shielded side of the antenna coax and an other
          > device connected to the Pi that wind up grounded via the AC powerline
          > neutral or grounding conductors. My theory is that the GPIO was
          > damaged by one of these means, or in some other way that I haven't
          > thought of yet.
          >
          > I think that one stage of isolation using a simple BJT amplifier would
          > provide cheap insurance, as would galvanic isolation between the antenna
          > and the Pi. I plan to try both when the replacement Pi arrives.
          > Meanwhile, I thought others could benefit from this experience.
          >
          > Any thoughts or theories on this would be appreciated as well,
          > especially by Guido and others who have been using Wsprry Pi longer than
          > I have.
          >
          > 73, Bob W9RAN
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
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