T/H BLE receiver - Blowed up good...Blowed up real good!

[DrG]

Going on ~two years ago, I built a little four channel, BLE receiver for remote humidity and temperature monitoring. The receiver is an ESP32 with a generic 4X20 LCD. It has been working like a charm and I am real happy with the project. Yesterday, however, I walked across the carpet, grabbed the unit, touching one of the four mounting screws that connects the LCD to the case and... bzzzzt ...static electric shock and instantly the screen went to those tell-tale squares where other characters should be. Resetting power produced no change.



After disassembly and further investigation, I determined that the 4X20 was fried and the ESP32 was fine. I happened to have another LCD and replaced the bad one and all is well.

Looking at the back of the LCD board, notice J1 and J2 solder bridge jumpers (they are not bridged). Also, each of the four mounting holes are connected (obverse side of the board and not shown). Thus if I connect J2, I would connect all four mounting screws to the ground plane.





Would that have make a difference? In general, is it a good idea to do so in a project with mounting to a case like this?


PS: I realize that the LCD screen may still be intact and something on the I2C board may have blown. I will investigate that possibility at some time in the future.

PPS: With regard to https://www.eevblog.com/forum/chat/i-constantly-getting-shocks-from-electrostatic-charge-what-can-i-do/ I favor misting diluted liquid fabric softener and regret not having done so.

[TheMG]

You also need to have a good low impedance path between the ground plane of the LCD module and the common/ground of the rest of your circuitry, and ultimately all the way to the ground/common of the power supply.

ESD discharges have a very fast rise time and wires will behave as inductors, allowing potentially damaging voltage differences to occur during ESD events. So keep impedance (inductance) to a minimum. In a metal enclosure this is not a problem as the enclosure provides a nice low impedance path, but in plastic you need to bond different boards/modules with larger gauge wire or even copper braid or copper tape.

[DrG]

You also need to have a good low impedance path between the ground plane of the LCD module and the common/ground of the rest of your circuitry, and ultimately all the way to the ground/common of the power supply.

ESD discharges have a very fast rise time and wires will behave as inductors, allowing potentially damaging voltage differences to occur during ESD events. So keep impedance (inductance) to a minimum. In a metal enclosure this is not a problem as the enclosure provides a nice low impedance path, but in plastic you need to bond different boards/modules with larger gauge wire or even copper braid or copper tape.

Would connecting GND to a large (say a five or six hole width) piece of copper tape on the circuit board help?