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RPi + Other Software Using level shifter based on 74HCT08

Discussion in 'Hardware Support' started by Alex B. Goode, 4 December 2016.

  1. Alex B. Goode

    Alex B. Goode New Member

    Messages:
    13
    Hardware:
    RPi2, RPi3
    Dear fellows

    Let me ask you please about using the level shifter based on 74HCT08.
    It is related for the scenario when WS2812b is connected via a level shifter because a data pin of the LED required 5V meanwhile GPIO of RPi gives 3.3V only...

    https://hyperion-project.org/wiki/Supported-hardware
    WS281X-PWM: Used to directly connect WS2812b

    It works for me, perfectly. I just want to understand why we need to cascade two ports.
    For me it looks like one port is enough for the job. Any hint would be much appreciated.


    [​IMG]
     
  2. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    Correct - you only need one pair of hct08 as your ws2812 only us a single signal.

    Ws2801 by contrast is spi attached and needs data and clock.
     
  3. Alex B. Goode

    Alex B. Goode New Member

    Messages:
    13
    Hardware:
    RPi2, RPi3
    Just a feedback from my side:
    maybe we'd better correct the description on this wiki page to reflect this idea?

    Therefore, we decided to insert a line buffer between the GPIO and the led string based on a simple 74HCT series IC (using cascaded NAND (74HCT00), OR (74HCT32), or AND (74HCT08) ports)

    I would put in in a way:

    Therefore, we decided to insert a line buffer between the GPIO and the led string based on a simple 74HCT series IC (using NAND (74HCT00), OR (74HCT32), or two cascaded AND (74HCT08) ports)

    ... Our board relies on NAND version of 74HCT so two cascaded ports are used...
     
  4. penfold42

    penfold42 Active Member

    Messages:
    746
    Hardware:
    RPi1/Zero, RPi2, RPi3, 32/64bit, +Arduino, +nodeMCU/ESP8266
    I probably need to add a section about my SPI based ws2812 driver too