Strange I2C problem (and solution)


Closed Thread
Results 1 to 3 of 3
  1. #1
    Join Date
    Nov 2006
    Posts
    70

    Default Strange I2C problem (and solution)

    I build a lot of data logging devices, and I frequently use a real time clock and a EEPROM memory IC with various PICS using an I2C interface. While testing a new prototype I noticed that voltage would frequently shift from ~5.6V (normal) to ~3.3V. After much desoldering and breadboarding, the problem appeared to be related to the the 10K pull-ups I was using for the I2C interface. Without the pull-ups the voltage stayed at 5.6. But the pull-ups are necessary. So after trying several hardware solutions, I simply set the SCL and SDA pins high early in the program, and keep them that way. This seems to fix the problem, but I am still a bit baffled by it. Why would the pull-ups cause a voltage drop?? Just thought I would share this in case anyone else sees something similar.

  2. #2
    timmers's Avatar
    timmers Guest


    Did you find this post helpful? Yes | No

    Default

    If the "other end" of the I2C bus is running off 3.3v, then the SDA and SCK will be pulled down to 3.3 + 0.6 ish volts. through the devices protection diodes to Vcc.

    Just a thought!

    Timmers.

  3. #3
    Join Date
    Nov 2006
    Posts
    70


    Did you find this post helpful? Yes | No

    Default

    Thanks Timmers, but everything is running off the same 5.6V. I'm still a bit mystified, but my best guess is that the regulator cannot put out enough current (I'm using an onboard regulator from another component, which is "supposed" to be able to support a microprocessor).

Similar Threads

  1. 16F877 HSERIN problem with 3th party software
    By RFsolution in forum mel PIC BASIC Pro
    Replies: 7
    Last Post: - 11th March 2009, 18:11
  2. I2C and MCP23016
    By keymuu in forum mel PIC BASIC Pro
    Replies: 19
    Last Post: - 14th January 2009, 12:27
  3. Interrupt problem ?
    By iugmoh in forum General
    Replies: 4
    Last Post: - 1st February 2008, 23:01
  4. Strange PortA behavior on 18F PIC
    By Terry in forum mel PIC BASIC Pro
    Replies: 8
    Last Post: - 17th August 2007, 23:31
  5. interupt & Sleep Problem - HELP!!
    By Santana in forum mel PIC BASIC Pro
    Replies: 3
    Last Post: - 23rd November 2004, 11:39

Members who have read this thread : 1

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts