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Re: Questions about T3mini and GT-320FW GPS

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  • Will
    Marcel, Thanks for the message. Yesterday I went back and rewired the tracker I am assembling. I removed any extra lengths of wire and adding an additional
    Message 1 of 5 , Jul 15, 2013
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      Marcel,

      Thanks for the message.

      Yesterday I went back and rewired the tracker I am assembling. I removed any extra lengths of wire and adding an additional amount of ferrite cores. That removed enough RF from the system to keep the T3-Mini from going nuts when the HT is at 4Watts, all fitting inside of a little Pelican 1030 case.

      Also, thanks to the wiki reference, I missed it when looking for information. The higher than expected power draw occurs even when just the T3-Mini is attached to the batteries, no GPS connected. 9-12 volts is a lot to send into a little linear regulator, so Ill add a small current limiting resistor in series to see if that helps to reduce current draw. I still do not understand the lower than expected 4.5 vs 5.0 out of the 78L05. I'll try adding a bit more filter capacitance; .1uf on the output is pretty small. Now that I have the actual schematic, I can do more troubleshooting.

      I also found the proper reference to the GPS unit. Looks like it flashes it's LED On/Off at a 1 sec per state rate. The data it is sending out is garbage though it looks to be structured in format suggesting I have something set wrong or the data that is being sent is KISS formatted. I am using putty to keyboard control the T3-Mini via USB, entering the 'SNOOP' command, GPS is on port B.

      By the way, does anyone know haw the 'HT-PTT' switch in OpenTracker Configuration correlates to the 'HT' Solder Pads on the tracker?

      More to follow as I learn more.

      Thanks again,

      Will - N7IPY
    • Will
      An update - Well Silly me, the voltage drop seen at the 5V pin is caused by the isolation diode D2 dropping about .45 volts. The regulator output is spot on 5
      Message 2 of 5 , Jul 16, 2013
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        An update -

        Well Silly me, the voltage drop seen at the 5V pin is caused by the isolation diode D2 dropping about .45 volts. The regulator output is spot on 5 Volts prior to the diode.

        The tracker and GPS are drawing 90ma at 8.9 volts which seems high. There is still a lot of heat generated at U1 the voltage regulator. To reduce the power loss, I think the only solution would be to remove U1 and replace the circuit with a VR that is better suited for higher input voltages, something like a LK112SM50.

        I am still unable to get the GPS unit to send usable data on the TTL Out line.

        I hate to say it, but I think I will need to scrap this hardware and replace it with the other companies SMT tracker. The feature set of the T3-Mini are awesome, but the power draw is too great and the GPS... well I don't think I know what to say about it.. I know the other set up works as my first tracker was based on it and it works fine, just a little more expensize.

        Will - N7IPY
      • Marcel S
        Willy, A few comments: - You should be using the RS232 output on the GPS for the argent products. See:
        Message 3 of 5 , Jul 16, 2013
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          Willy,

          A few comments:

          - You should be using the RS232 output on the GPS for the argent products.
          See: https://www.argentdata.com/catalog/product_info.php?products_id=144 Be
          sure to use the correct cable pinouts from the GPS and try again. Hopefully
          that will solve the GPS part of the problem.

          - The currents you are reporting seem to be ballpark ok. The OT3m normally
          draws 40mA (so I presume the mini is in the same range (I don't have one
          here to check)). The GPS will draw <45mA (
          http://www.argentdata.com/files/GT-320FW.pdf) so the 90mA you are reporting
          doesn't seem far off from what you would expect. Keep in mind the 78L05UA
          regulator in use maxes out at 100mA, so if you're measuring the 90mA on the
          input, then there is a good chance it's being overdriven. You might want to
          check the GPS current inline and double check your wiring in case something
          is shorting and causing the regulator to max out. That regulator is
          designed to handle the tracker plus a GPS puck.

          I hope this helps out a bit. Keep us posted with your progress!

          Cheers,

          -Marcel AI6MS

          On Tue, Jul 16, 2013 at 7:39 AM, Will <engineer1@...> wrote:

          > **
          >
          >
          > An update -
          >
          > Well Silly me, the voltage drop seen at the 5V pin is caused by the
          > isolation diode D2 dropping about .45 volts. The regulator output is spot
          > on 5 Volts prior to the diode.
          >
          > The tracker and GPS are drawing 90ma at 8.9 volts which seems high. There
          > is still a lot of heat generated at U1 the voltage regulator. To reduce the
          > power loss, I think the only solution would be to remove U1 and replace the
          > circuit with a VR that is better suited for higher input voltages,
          > something like a LK112SM50.
          >
          > I am still unable to get the GPS unit to send usable data on the TTL Out
          > line.
          >
          > I hate to say it, but I think I will need to scrap this hardware and
          > replace it with the other companies SMT tracker. The feature set of the
          > T3-Mini are awesome, but the power draw is too great and the GPS... well I
          > don't think I know what to say about it.. I know the other set up works as
          > my first tracker was based on it and it works fine, just a little more
          > expensize.
          >
          > Will - N7IPY
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