Need help on long distance (>1.5m) SPI bus.

Discussion in 'General Electronics Chat' started by rexma, Dec 8, 2008.

  1. rexma

    Thread Starter New Member

    Dec 8, 2008
    the problem is, the spi device is far away from the mcu. it's quite unstable.

    3.3V MCU SPI clk/data --------- >1.5m track---------> device

    someone suggested me to use a buffer(74hct245) to convert 3.3v signal to 5V and add pull-up resistors.

    3.3V MCU SPI clk/data -->74hct245-->5V pull-up res --> device

    i really need more advice.
    thx. :)
  2. Papabravo


    Feb 24, 2006
    How fast is the clock that you are using. The use of a driver chip with more current drive will help on a long cable which looks like a capacitive load. Using a Schmitt Trigger on the input will help also.

    A better solution might be to use a differential line driver and receiver. Proper termination of the transmission line will also help to control reflections.
    Last edited: Dec 9, 2008
  3. rexma

    Thread Starter New Member

    Dec 8, 2008
    thx for your reply. :)
    I use a schmitt trigger buffer NL27WZ17. And it works!