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  • uLCD-70DT PWM offset issue.

    HI Team,

    I am facing an issue with uLCD-70DT PWM. I am receiving an offset of 8.8 mV. Could you please help me with if there is anything that can be done to bring this to zero as If not, I will have to tare the offset using an analog circuitry later.

    Regards,
    Suraj.P

  • #2
    What do you mean by offset?

    By definition, I would have thought, there is no such thing as an offset in PWM
    Mark

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    • #3
      Dear Mark,

      We have 1000 divisions to achieve 3.3V so for say for a value of 2 I am expecting 6.6mV, for 1 3.3mV and for 20 66 mV. But, I see an addition of 8 mV in all of these reading. For 1 I get like 8.8mV, for 2 15.23 mV for 3 the value is 15.23 mV.

      Regards,
      Suraj.P

      Comment


      • #4
        Can you show some code that shows this? And perhaps how you are connecting/using the hardware?
        Mark

        Comment


        • #5
          The code uses pwm_init(PA4,1,x) where x is used to vary the value of mV by using the 1000 divisions as suggested in datasheet. The hardware connection is just taking the voltage in multimeter voltage value between the PA4 and GND.

          Regards,
          Suraj.P

          Comment


          • #6
            PWM is Pulse Width Modulation.

            So the output is either 0 or 3.3v and the amount of time it is 0 or 3.3v is adjusted by the value.

            To turn it into a steady voltage between 0 and 3.3v requires filtering. To try and measure a voltage directly on a multimeter will almost certainly result in an unexpected reading.

            Having said that, are you sure that the gnd you are measuring the voltage relative to is the same gnd that the display has? Depending where you take your ground from 8mv could easily have been 'introduced'
            Mark

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            • #7
              Dear Mark,

              I am using the GND pin in the port of uLCD70DT itself to measure the voltage. I totally understand that it would need a RC filtering, though I was of the idea that the Multimeter measures the RMS voltage when given to PWM and can be of use to measure the exact voltage.

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