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Re: [SeattleRobotics] Serial Cable to USB Cable Hack

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  • Randy Carter
    The thing to consider is, whether or not there are some electronics in the meter s cable. The signal levels on the meter s port could be TTL levels and the
    Message 1 of 3 , Dec 2, 2005
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      The thing to consider is, whether or not there are some electronics in
      the meter's cable. The signal levels on the meter's port could be TTL
      levels and the cable has the level shifters to make RS232. There are so
      phantom powered RS232 level shifters that don't require an external
      power supply.

      The USB to serial adapter plug isn't simple. It is a special chip that
      receives commands from the USB (only 4 wires, 2 of those are power) and
      translates them into commands for a UART. There aren't just the 2 data
      signals (TXD and RXD) there are also 4 handshaking and ring indicator
      (RI) signals generated. In addition this adapter has the level shifters
      to take TTL's 0 to 5 volt signals to the +12 and -12 volt signals used
      by RS232.

      > Jason Travis wrote:
      > Hello -
      >
      > I have a diabetic testing meter that did not come with
      > a computer cable. I have the software that came with
      > it. I would like to hack together my own cable as the
      > proprietary one is $50 ($40 for the serial cable and
      > $10 for the usb-to-serial adapter plug). The end of
      > the cable that plugs into the meter is a 1/8" phone
      > plug. I know that for the serial cable the ground of
      > the phone plug goes to pin 5, the stripe goes to pin
      > 3, and the tip goes to pin 2, of the serial plug,
      > respectively. If I simply find the ground, positive
      > voltage and data pin on the USB will this work? Also,
      > since the program is written for the serial cable
      > (even though they provide a USB adapter) do I have to
      > obtain a plug-in software driver? Or will the native
      > USB drivers in XP automatically connect? Do you think
      > the USB-to-serial adapter they provide comes with a
      > software driver?
      >
      > Thanks in advance for your help.
      >
      > Jason Travis
      >
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