Hi, I'm studying the Nano 33 Iot schematic for educational purpose and I want to understand all the components' purpose. For instance, why do C1 and R1 and placed there and where are they specifically connected? Ground and...? The USB connector plates? Thanks to everybody, and sorry for my english (I'm not a native speaker!)
Hard to say with just a snippet of the schematic, but, my guess you are looking at part of the wifi antenna.
They ground the shield on the USB connector to induced RF and electrostatic voltages.
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Thanks a lot! Could you please explain what you mean saying "induced RF"? Sorry, I'm not native speaker!
Sorry, I should have been more specific. The schematics shows the supply circuit: you can see the micro USB connector and the data bus D+ D- are placed in input to the microcontroller.
@riccardo_brudaglio02
Don't assume that any Arduino schematic you see is correct. Many have mistakes and that is one.
The diode array should have been connected to Ground, not the 1M resistor.
The usefulness of the RC network is debatable, many designs just leave the USB shield unconnected.
Voltages in the USB shield that might arise when exposed to radio frequency transmissions (if not grounded by a small capacitor).
The idea is probably that the impedance of the 4n7/1kV capacitor is negligible for the kind of discharge the TVS diode array is intended to protect against. A further explanation is possibly that they wanted to prevent the TVS array to fry if for whatever reason someone manages to apply a reverse voltage on VUSB + GND (making GND more positive than VUSB). Apparently D2 (a much more robust PMEG6020) series diode between VUSB and VIN acts as a rudimentary polarity protection instead.
The way I interpret this is that it's intended to keep as much of the magic smoke from escaping under as wide a range of circumstances, but without going overboard in terms of parts count. It's a compromise, and not the most common one, but I think it makes some sense.
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