Voltage drop on Arduino Due I/O pin.

Discussion in 'Embedded Systems and Microcontrollers' started by rentiantong123, Mar 31, 2015.

  1. rentiantong123

    Thread Starter New Member

    Mar 29, 2014
    23
    1
    I am using Arduino Due to control BJT switch array.
    Schematic is as follow (attachment):

    I am able to get 3.3v output voltage from Arduino. The problem is that once I connect it as schematic shows, the output voltage drops to 0.6v.
    Arduino Due pins can give output current as high as 40mA, but this circuit gives me only 0.0266mA (by calculation).
    When using 3.1V battery, the circuit works fine and gives 1.23mA current.

    Can anyone help me?
    Thank you
     
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  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    Are you sure you have the MCU pin set as an Output and not an Input.?
    If the internal pulls ups are enabled its possible that the pin is pulling High off load.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,651
    632
    If the collector load is an LED inside of an optical isolator then it might be that when the Arduino output pin goes high, the current through the transistor's collector pulls the power supply out of regulation, the result being that the power supply and therefore the output of the Arduino will be regulated at a voltage that is just enough to drive the transistor at the level that pulls the supply out of regulation.

    You can check for this condition by measuring the voltage between VCC and VSS of the Arduino or by disconnecting the optical isolator.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    To make sure that you connected to the right pins of transistor.
     
  5. JWHassler

    Member

    Sep 25, 2013
    201
    33
    Is that .6V measured at the output pin or at the transistor base? In the second case, it would be correct.
     
  6. rentiantong123

    Thread Starter New Member

    Mar 29, 2014
    23
    1
    Thanks for your reply.
    I only used "digitalWrite(xx, HIGH);" to set pin to 3.3V.
    I will try it right now.
    Do I have to use "pinMode(xx, OUTPUT);" to set it as output? Why I still can get 3.3V without this?
     
  7. rentiantong123

    Thread Starter New Member

    Mar 29, 2014
    23
    1
    Thanks for your reply, sir.
    The problem is that the circuit works with a 3.1 battery.
     
  8. rentiantong123

    Thread Starter New Member

    Mar 29, 2014
    23
    1
    It works now.
    Thanks so much for your help.
     
    ErnieM likes this.
  9. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
    2,831
    89
    Hello,
    From circuit you posted change 71.5K to 10K and base 2K to 440 ohms will delivery maximum current!
     
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