logic level converters and rpi etc

Discussion in 'Embedded Systems and Microcontrollers' started by pibeans, Jan 12, 2013.

  1. pibeans

    Thread Starter New Member

    Jan 11, 2013
    First post - and hope its in the right place.

    I am newly returned to electronics having been re-enthused by the r-pi and at the same time discovering the arduinos.

    I understand the need to do logic level conversion from the RPI's 3.3v GPIO to most real projects.

    Am I right in thinking I just need to do this on the data & clock (and chip-select) lines of the I2C or SPI assuming I am using either of these to talk to the rest of the project?

    TIA / pibeans
  2. kubeek


    Sep 20, 2005
    Depends, if the circuit you are interfacing runs on 3.3V then you don´t need any conversion.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    I've basically come to the conclusion a year or two ago that in complex microcontrollers there was a paradigm shift away from the fixed 5 volt supply to somewhere around 3.3 volts.

    The trick today is to look for the other parts to have a compatible supply voltage: my current project's I2C runs at 3.3 cause all the chips do.

    5 volts isn't going away, and there are several techniques to handle the transition, from just a simple resistor* to voltage level translating IC's such as a 3.3 to 5V I2C translator I once needed: yet, it translates signals in both directions.

    Exactly what needs to be translated needs to be handled on a case by case basis.

    * If your device has 5V tolerant I/O pins you can use a pull-up resistor to get a 5V high by making that pin an input, then make it an output set to 0 for a low output.
    Last edited: Jan 12, 2013
  4. pibeans

    Thread Starter New Member

    Jan 11, 2013

    I've already built several PI GPIO projects with I2C and SPI with ADCs and expanders in both flavours - but everything so far at 3.3v.

    I now need to start mixing in some 5v devices. So I've ordered up a couple of 4ch bi-dir converters that do both I2C and SPI.

    I see the need now to cover all lines.