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XBee Modules and the BASIC Stamp — Parallax Forums

XBee Modules and the BASIC Stamp

velociostrichvelociostrich Posts: 40
edited 2009-08-28 10:35 in BASIC Stamp
I bought two XBee modules for a project of mine, but from what I've read, stamps cannot directly output signals to the XBee, given their 5V logic levels as compared to the XBee's 3.3V.

I see that the AppBee from SelmaWare uses the 74LVC244A to "condition" the BASIC Stamp's 5V logic levels to the XBee's 3.3 -- an IC that I don't have -- so I'd like to know if it is possible to just use resistors.

Furthermore, does the XBee require its own voltage regulator (at 3.3V)? I would assume that because of its variable current draw, I could not "just" use resistors, right?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2009-08-27 23:59
    The xBee does require a 3.3V regulated power supply and you can't use "just a resistor". You'll need a voltage regulator of some sort.

    I don't know for sure if a series resistor in each Stamp output to xBee input connection will work. Try a 3.3K or 4.7K resistor to limit the input fault current to a couple of hundred microAmps. The 74LVC244A or other voltage translator would be better, but the resistors may be enough.
  • Ron CzapalaRon Czapala Posts: 2,418
    edited 2009-08-28 00:24
    AdaFruit sells an XBee Adapter kit which has a 3.3V regulator·and level shifting circuitry that lets you connect easily to a 5v microcontroller for $10.

    Link:
    http://www.adafruit.com/index.php?main_page=product_info&cPath=29&products_id=126
  • xanatosxanatos Posts: 1,120
    edited 2009-08-28 00:35
    I have been using with great success the LM2937ET-3.3 regulator for the XBee XSC (which draws more current on TX (265mA) so it may be more current available than you need), and a 1.5k and 3.3k resistor voltage divider on the TX and RX leads into the XBee from the stamp. The stamp at the top of the ladder, into the 1.5k to the XBee, then through the 3.3k to ground. Flawless, cheap, tiny if you use SM components. Some XBees inputs are "5V Tolerant", but they do not recommend long term use at the full 5V. The voltage divider scheme in combination with 5V "tolerant" inputs should be perfect. I have a few projects in the field now that have been running continuously for a couple of months now using this setup.

    Dave
  • velociostrichvelociostrich Posts: 40
    edited 2009-08-28 01:21
    Thanks for all the replies.

    Xanatos, your solution sounds wonderful -- I'll give that a try.
  • dev/nulldev/null Posts: 381
    edited 2009-08-28 10:35
    There are numerous ready-made CMOS-TTL converters available. SparkFun has one.

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