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Interfacing 5v to 3.3V UART

Discussion in 'Electronic Basics' started by GNU, Jun 4, 2004.

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  1. GNU

    GNU Guest

    I want to comminicate two UARTs : 3.3V (UART1 Vinmax = 3.7V) with a TTL
    one (UART2 5V) from 9600Baud to 250Kb/s like this :

    UART1 (TTL 5V) UART2 (3.3V)
    TX1 ------------> RX2
    RX1 <----------- TX2

    From TX2->RX1, i think there's no problème. My question is how to
    interface Tx1&RX2, The first sends 5v to Rx2 wich accepts only 3.3
    signals. Need your help please.
  2. Soeren

    Soeren Guest

    Hi Tarek,

    That depends on the hi/lo-levels, but you might get away with a direct
    coupling (if not, add 2 transistors to convert the voltages).

    Use a resistor and a zener diode like this:

    TX1 ---[1k5]---+----- RX2
    / /_\ Z3V3
    Gnd -----------+----- Gnd


    * If it puzzles you dear... Reverse engineer *
    New forum: <URL:>
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