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Protecting self-built UM2 from ESD


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Posted (edited) · Protecting self-built UM2 from ESD


I have built my own UM2 with aluminum extrusion profiles as frame and some

minor modifications to make it slightly taller than the UM2 extended.

The aluminum extrusion frame is covered with composite aluminum panels ("dibond-like").

The control knob is a solid one made of anodized aluminum (see image below).


I used a switched power supply 24V/10A with AC ground connected to the aluminum frame.

For the testing however, I used the output of a stabilized lab power supply (so that I could also

see the actual current drawn) but I did not connect the ground of that supply to my UM2 frame during the test.

When touching the control knob on the Ulticontroller v2.1, an electrostatic discharge (ESD) occured which took out the controller: the display and knob leds went out and I could smell that something had fried.

Inspection of the PCB showed that chip U3 on the PCB (the PCA9306 chip: Dual Bidirectional I2C Bus and SMBus Voltage-Level Translator) was fried: the package shows a hump on the top (see image below)


I will try to replace that component, hoping that the damage was limited to that one alone and did not propagate to other parts of the circuitry, especially the main board.

But how can I effectively protect my UM2 against such ESD damage in the future? Was the choice of using an aluminum knob a bad one since it provided a discharge path into the circuitry?

Thanks for sharing your insights on this!



Edited by Guest
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    Posted · Protecting self-built UM2 from ESD

    Could you either put in an insulating section into the rotary encoder shaft or fit an earthing 'wiper' onto the knob?

    ESDs aren't as common as they once were, components tend to be more robust now.


    I will answer my question myself... I should indeed have used a non-metallic knob, or have replaced the rotary encoder on the PCB by one with a plastic shaft.

    But since I really like this aluminum knob and don't want to replace the rotary encoder on the PCB, I will try to find a way to insulate the knob from the rotary shaft somehow.

    I guess this was a stupid beginner's mistake. Even though this is the first time I ever built something, I should have known better...


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    Posted · Protecting self-built UM2 from ESD

    Hi John,

    I tested the UM2 in a location with bad flooring, and regularly get ESD discharges when touching the door knob. I mentioned this problem to the persons in charge there and they will consider installing some grounded mat or something. In any case, I should probably wear a grounding wrist wrap, and drink more water...

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