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Temperature stability

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  • scott@opentrac.org
    Hi everyone, thanks for joining the group. I was starting to have trouble getting the latest updates to everyone - hopefully this ll work out better. I did
    Message 1 of 3 , Mar 14, 2006
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      Hi everyone, thanks for joining the group. I was starting to have trouble
      getting the latest updates to everyone - hopefully this'll work out better.

      I did some cold testing on the T2 board over the weekend, and found that the
      receive side stopped working below a certain temperature. I'm not sure what
      temperature that was, since I don't have a thermometer that goes below -50C.
      I think the stability is good enough for consumer applications, assuming it
      can handle high temperatures as well, but I'd like to do better than that
      for applications like high altitude balloons.

      I've ordered some C0G-rated capacitors to replace the X7R-rated ones
      currently used in the demodulator circuit. A couple of them are already
      very stable metal film types. I also ordered some metal film resistors with
      1% tolerances and much more stable temperature characteristics. I'm not
      sure if they're going to make that much difference, but we'll see. Could be
      that the '2211 chip itself doesn't like the cold.

      I'm going to experiment with bypassing the input filter network - I'm
      curious just how much good it actually does.

      If anyone wants KISS mode firmware, let me know and I'll get a file uploaded
      for testing. Digipeating probably won't be ready for testing until this
      weekend.

      One issue that's come up with the current T2 design is that some GPS
      receivers like the GPS 3+ require true RS-232 levels to work right. That's
      going to require either an external adapter board, or a transceiver chip on
      the T2. I can probably squeeze one in, but it'll raise the cost by around
      $2, and the power consumption by 5 to 10 mA.

      Scott
    • Curt Mills
      ... I m definitely interested in testing the KISS firmware. Problem is, I don t even know what the board looks like yet... ... Most devices these days will
      Message 2 of 3 , Mar 14, 2006
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        On Tue, 14 Mar 2006 scott@... wrote:

        > If anyone wants KISS mode firmware, let me know and I'll get a file uploaded
        > for testing. Digipeating probably won't be ready for testing until this
        > weekend.

        I'm definitely interested in testing the KISS firmware. Problem is,
        I don't even know what the board looks like yet...


        > One issue that's come up with the current T2 design is that some GPS
        > receivers like the GPS 3+ require true RS-232 levels to work right. That's
        > going to require either an external adapter board, or a transceiver chip on
        > the T2. I can probably squeeze one in, but it'll raise the cost by around
        > $2, and the power consumption by 5 to 10 mA.

        Most devices these days will work with 0-5V or even 0-3V. I'd make
        it an external board and keep the T2 small/light.

        --
        Curt, WE7U. archer at eskimo dot com
        http://www.eskimo.com/~archer
        Lotto: A tax on people who are bad at math. - unknown
        Windows: Microsoft's tax on computer illiterates. - WE7U.
        The world DOES revolve around me: I picked the coordinate system!"
      • scott@opentrac.org
        ... Ok, it s posted. Use the web button to grab it. It s just a single-bit difference in a constant.. haven t had a chance to make it a config option yet.
        Message 3 of 3 , Mar 14, 2006
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          > I'm definitely interested in testing the KISS firmware. Problem is,
          > I don't even know what the board looks like yet...

          Ok, it's posted. Use the 'web' button to grab it. It's just a single-bit
          difference in a constant.. haven't had a chance to make it a config option
          yet. Oh, and it's hardcoded at 4800 baud for the moment.

          > Most devices these days will work with 0-5V or even 0-3V. I'd make
          > it an external board and keep the T2 small/light.

          I'm going to throw together an adapter board with an ST202 or something
          similar... really only needs a single non-inverting transmitter. It could
          go in a C6 case, but the C6 won't fit on the OT2m without blocking the radio
          port. A C4 might work, but would probably require some retooling. Or I
          could go with SMT and try to squeeze the whole thing in a DB9 shell. Hmm..
          know of any good metallized shells that have DB9s on both ends?

          I've been so busy with other stuff, I've hardly had a chance to touch the T2
          since Sunday. I did get the PSK31 firmware modified to allow carrier
          frequency selection, though... I'm proud of that. Thought it was going to
          be a real pain, but it worked way better than I expected. DigiPan decodes
          it all the way from 62.5 hz all the way up to almost 8 khz - and with a
          sample rate of 11 ksps, so it's decoding a Nyquist image! Didn't think the
          signal would hold up that well.

          Scott
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