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Connecting a 5.0V UART to a 3.3V UART

Discussion in 'General Electronics' started by Susanne Fischer, Jun 16, 2004.

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  1. Hi!

    I have a Microcontroller (Fujitsu MB90F347) running with 5.0V supply
    voltage and a bluetooth module (Zeevo 3001Z) with 3.3V. Now I want to
    connect them over UART.
    Usually I would connect them directly. But this might not be possible
    because of the different voltage levels.
    Is there a simple solution how to do that? Perhaps I could convert the
    signal twice using a MAX232 or similar. But as I wrote in a previous
    thread, this somehow doesn't work. But I don't know why not. Any idea?

    This brings me into serious trouble since I am not able to do further
    work on this whole stuff and I have to match some deadlines. I am
    really helpless because I just don't understand why this whole thing
    doesn't work...

    If anyone has an idea how to make communication possible, please help
    Thanks in advance,
    Susanne Fischer
  2. Quack

    Quack Guest

    I havent tried this, but it seems to make sense, it seems a simple
    approach :)

    The Fujitsu RX pin should be able to connect directly to the Zeevo 3v
    TX pin, and get a clear signal.

    The Zeevo RX pin should use a 2.5v zenner diode, to cut the incoming
    5v signal down the that voltage.
    One of them may be using 'inverted' comms, the other 'true'.

    You can use a couple of transistors and a few resistors to make a
    2-way inverter if necesary, i have done this before.

    I dont think using 2 MAX232 chips would help if 1 of them is opposite.

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