Microcontroller's output signal measurement

Discussion in 'Embedded Systems and Microcontrollers' started by Steven01, Oct 3, 2016.

  1. Steven01

    Thread Starter New Member

    Oct 3, 2016
    4
    0
    Hello,

    I have some control board equipped with a microcontroller.
    This control board is supplied by 24V laboratory voltage source. I
    would like to measure signals on some microcontroller's
    output pin with a digital oscilloscope. I have only two common
    probes with earthed alligator jack connector. I am not sure
    whether the measurement with a probe connected to the output
    pin and alligator jack connector connected to minus pole of the
    voltage source is correct. Would be better to use both probes
    with their alligator jacks connected together and then connect
    the first probe on the microcontroller's output pin, the second
    probe to the minus pole of the voltage source and use ChA-ChB
    function? Thanks.
     
  2. jayanthd

    Member

    Jul 4, 2015
    274
    29
    An Oscilloscope will have a probe and in the probe there will be actually two probes. The longer probe is for +ve and the shorter probe of the same cable is for -ve. Connect the longer probe to microcontroller pin and the shorter probe to the ground (in single power supply -ve will be ground) in dual (+ve and -ve power supplies -ve is not ground).

    If the microcontroller pin you are measuring is toggling then you will see a pulse (0 to 5V) on the scope.
     
  3. Steven01

    Thread Starter New Member

    Oct 3, 2016
    4
    0
    Thank you for your answer Jayanthd.
    I supply the control board from a floating
    laboratory voltage source. Please can you
    tell me where to connect the ground of the
    oscilloscope's probe in this situation
    (-ve is not ground)? I would like to apologize
    to my silly question but I am an autodidact
    and I haven't yet fully understand floating
    measurements. Thanks.
     
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    This will work fine as long as the PSU negative is earthed or there is no earth connection. It will only be a problem if some part of the circuit or the positive PSU connection is earthed.
     
  5. jayanthd

    Member

    Jul 4, 2015
    274
    29
    If your power supply provides both =ve and -ve voltages like +5V and -5V then -ve is not ground. If your PSU gives only +ve voltages like +5V, +30V then -ve is ground (0V). To measure the voltage at the pin of a microcontroller in +ve only power supply you connect the bigger probe to MCU pin and -ve (smaller probe of the same cable) to the -ve of the circuits power supply.
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    I don't recognise this description of a 'scope probe. This picture shows what I know as a 'scope probe. It has a grounding clip and the probe tip itself (in this case a clip) and this is the kind described by the TS.
    [​IMG]
     
  7. jayanthd

    Member

    Jul 4, 2015
    274
    29
    I meant the same thing.
     
  8. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    The alligator clip is the smaller probe?
     
  9. jayanthd

    Member

    Jul 4, 2015
    274
    29
    Yes and the gray longer probe is for connecting to +ve or -ve lines and alligator clip for ground.
     
  10. Steven01

    Thread Starter New Member

    Oct 3, 2016
    4
    0
    Thank you all for your answers. Can somebody recommend me some
    book or article about grounds and measurements? Thanks.
     
  11. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,968
    387
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