Arduino pulsing output

Discussion in 'Embedded Systems and Microcontrollers' started by Alasttt, May 13, 2015.

  1. Alasttt

    Thread Starter Member

    May 13, 2015
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    0
    Hi all,

    I want to get a square wave that goes between +2v and -2v. From the arduino outputing HIGH then LOW gives a square wave between 0v and 5v. Any ideas on how I could change the arduino configuration to output different voltages for high and low. or alternatively how to use electronics to convert the 0-5 into -2 to +2
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,178
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    Sure -- run your [0-5V] signal into a summing amplifier with a constant input of -2.5 volts and a gain of 0.8
    (0 - 2.5)*0.8 = -2.00
    (5 - 2.5)*0.8 = +2.00
     
  3. Alasttt

    Thread Starter Member

    May 13, 2015
    68
    0
    Hi thanks. I have also heard putting a capacitor after it will AC couple it and have the same affect to make it +2 to -2. Would you agree ?. Since this might be easier then a summing amp.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,178
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    No. A series, or DC blocking, capacitor will change the square wave into a series of sharp impulses with exponential decay. Not what you are looking for.
     
  5. Alasttt

    Thread Starter Member

    May 13, 2015
    68
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    Right ok thanks. Please could you tell me where could I get the constant input of 2.5v from ?.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,178
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    A voltage divider.
     
  7. Alasttt

    Thread Starter Member

    May 13, 2015
    68
    0
    Right thanks. Youve specified gain to be 0.8. Gain is Rf/Rin.

    So for the op amp, I connect the - input to +2.5v. connect the + input to the 0-5v square wave via a 10 ohm resistor, and make Rf 8 ohms.
    This gives 8/10 which is a gain of 0.8.

    Correct?
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The best you can do without an opamp. If you use an opamp, remember that you will need a negative power supply, like -5V 211.gif
     
  9. Alasttt

    Thread Starter Member

    May 13, 2015
    68
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    Thanks. Do you know if thers a way of changing the arduinos internal ADC voltage reference ?
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    To what end?

    Download and study the ATmega chip data sheet. I'm sure it can be done, but not likely through the Arduino supplied library.
     
  11. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    684
    92

    What he said.

    http://forum.allaboutcircuits.com/gallery/photos/a-summing-amplifier.2957/

    [​IMG]
     
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