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16X2 LCD display problem while measuring AC current

Discussion in 'Microcontrollers, Programming and IoT' started by Fahad Sadaqat, Feb 24, 2017.

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  1. Fahad Sadaqat

    Fahad Sadaqat

    5
    0
    Jan 28, 2017
    Hello,

    I am doing this project that measures AC current and then displays it on a 16X2 LCD. Everything works fine except that when I toggle the switch to turn the load on or off, the LCD display starts to show random characters or just disappears. I faced this problem once before when I was working on a Power line communication project. This thing happened there as well. It also involved AC interaction with the circuit. I have searched the web but didn't find any relevant solutions. I should mention that I am using a relay but that isn't the reason why the LCD is malfunctioning. It only happens when I switch the load (which in this case is a 100 Watt light bulb).

    Any help of any sort would be highly appreciated.
    Thank you.
     
  2. Minder

    Minder

    3,003
    638
    Apr 24, 2015
    You most likely need better decoupling of the LCD supply, or galvanically isolate the LCD circuit from the AC power.
    Is the relay switching the Lamp?
    Whatever is switching it, a R/C snubber across the switching element may work also.
    M.
     
  3. Fahad Sadaqat

    Fahad Sadaqat

    5
    0
    Jan 28, 2017
    The problem only arises whenever any of the switches in AC circuit is toggled or in other words whenever the AC load is turned ON/OFF or increased/decreased. No matter if its the relay or a manually operated switch.
    What if I power the LCD with another power supply which only powers the LCD and no other component? would it help? Because I have many switching components and it wouldn't be possible to attach snubber across each one of them?
     
  4. Minder

    Minder

    3,003
    638
    Apr 24, 2015
    Ensure you DC is decoupled properly with sufficient capacitance across the supply.
    Using an isolated supply for the LCD and low voltage circuitry may help.
    M.
     
    CDRIVE, Arouse1973 and Fahad Sadaqat like this.
  5. Fahad Sadaqat

    Fahad Sadaqat

    5
    0
    Jan 28, 2017
    Thanks a lot Minder. Adding a 47uF capacitor across the power supply and powering the Arduino through a 9V battery instead of plugging it into my laptop solved the problem. The LCD works fine now. Thank you once again.

    Regards
    Sadaqat
     
  6. muhammad iqbal

    muhammad iqbal

    1
    0
    Sep 13, 2012
    Please first isolate the supply of microcontrollar from AC power and use current transformer for measurement.Then use filtering capacitor of at least 1000uf before 7805 regulator and also connect 10k resister on reset pin of controller and 5volt and connect 10uf capacitor on reset pin and ground.
     
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