Hi. Looking at the schematic for the arduino every there is a diode matrix labeled D1 that connects to VUSB and yet the negative end of D1 zener goes through a resistor and capacitor in parallel to ground. Should this not go direct to ground to be of any benefit, or am I missing something too obvious.
Thank you, John
Others can probably provide a better answer, but I think it's a crowbar circuit and that its proximity to the LED array is not important.
You need to understand the difference between GROUND and SHIELD.
The GROUND pin is the both the negative of the supply voltage and a reference for signals, a SHIELD is used to deflect noise and static charge.
Static charge can have a high voltage (though little power), so the capacitor is rated for that while a large resistance is enough to keep the metal parts near ground potential.
Hi. So the zener diode isn't there to protect the usb input from voltage spikes, like if we were to use a tvs diode. I've been into electronics for over fifty years, and have seen some very interesting circuits. I assumed the zener was for rudimentary ov protection. Thank for explaining.
Yes it is!
Why do you think it's there.
However in my opinion that schematic is wrong. The ESD diodes should be returned to ground, not to the shield.
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Yes, I think it's wrong too.
I agree, you’d expect that pin to be connected to the ground. The datasheet even says so.
For high-frequency spikes the capacitor makes it work still. It would take specilized equipment to measure the difference in performance.
By the way: I measured 1MΩ between that pin and GND, so it’s not a deviation of documentation from the board.
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Curiosity piqued: you can see in the schematic that the cathode of D1 is also connected to the USB connector's shield. When a USB cable is plugged in, the shield is grounded by the host. So the negative end of D1 is connected to ground when connected to the host.
No. USB cables are usually unshielded, twisted pairs. However, any exposed metal parts need to be grounded in some way for protection of humans. The capacitor / resistance combo is enough to comply with regulations..
And yet the 3 cables I tested on before posting were all shielded. Go figure.
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The info of unshielded comes from USB-standards. I did a measurement too. The USB cable I use to connect my Nano Every does connect the metal parts at both ends. But: the metal part of the receptacle of the Nano Every does not connect to the metal part of the cable. So that’s not something you should trust.
My conclusion at this point is: the protection circuit works, though probably not as good as could have been.
You must have a very unusual Nano Every with a very unusual USB micro connector then.
I tested 2 other microUSB cables I have lying around: no connection between the metal parts at the ends (no shielding), connection between cable and receptacle. The cable I tested before shows intermittent contact to the receptacle (corrosion?).
Still: not something you should trust.
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