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Thread: static discharge confusing 1602 display, precautions?

  1. #1

    static discharge confusing 1602 display, precautions?

    I have an aluminium project box containing a 3.2, W5500 board, 1602 i2c display and rotary breakout which is itermittently freaking out when (the rotary encoder is) touched. First i was looking at my sketch and have been letting it sit for timed intervals before moving the rotary, but the last time it scrambled was on initial touch and i heard a small pop in my speakers leading me to suspect a static discharge.

    This box is usb powered but i want to make an externally powered version with buck converter taking 12V input down to 5V. I understood having a 100uF and 10nF capaciter on the buck converter input and output could help?

    Are there any basic precautions i can take circuit wise to protect the system from static?


  2. #2
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    Best is to connect all box panels to ground, at a point near the connectors mounted on the box.

    It is unclear how your externally powered version will get it's power. From a PC, a wall wart, built in power supply working from the mains voltage ? Same idea though is to hook the box to the power supply ground where it enters the box. For the mains powered version, connect the box to the third terminal safety ground (green wire in US).

  3. #3
    Quote Originally Posted by grease_lighting View Post
    Best is to connect all box panels to ground, at a point near the connectors mounted on the box.
    With panels do you mean the aluminium enclosure panels or the LCD and encoder?

    Quote Originally Posted by grease_lighting View Post
    It is unclear how your externally powered version will get it's power. From a PC, a wall wart, built in power supply working from the mains voltage ? Same idea though is to hook the box to the power supply ground where it enters the box. For the mains powered version, connect the box to the third terminal safety ground (green wire in US).
    The powered version will be PoE from an external injector. The W5500 board will be the newer compact kind in combination with PJRC WIZ820io & Micro SD Card Adaptor. The schematic is pretty barebones:



    I just found a discussion on stackexchange which leads me to believe i need to do more to keep the i2c bus happy:

    https://electronics.stackexchange.co...t891652_369365

    here's an outtake:
    You should have 100nF between VDD and GND wires at each end of your I2C cable. This ensures that both these wires act as AC ground.

    You should put VDD and VSS between SDA and SCL and not put SCL next to SDA or make them the same twisted pair.

    I commonly put 47ohm in series with SDA and SCL. This does not affect the normal levels, but does limit current in some faults, and damp down high frequency ringing.

  4. #4
    just to follow up on this. Since i became aware of static discharge being the source of the scrambles/freezes it hasn't happened again. I was initially grounding myself before touching the box and then changed the knob to a plastic one. The board in this box is a proto'd vero but i'll take the ground paths and chassis grounding into account in future uterations.

  5. #5
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    Panels as in box panels. They will usually be the first ones touched. Like when the user picks up the control box.

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