I'm making a 5 volt portable regulated power supply (using LM7805 regulator IC) for Arduino UNO. I'm planning to use a USB connector as its output socket, this way I can just plug it into the Arduino to power it.

My problem is where do I connect the USB sockets's shield? (Not an Arduino shield - I am talking about the USB cable's shield).

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As far as I know it should be connected to the ground if it is a host device - can we consider the power supply as a host device?

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    – SDsolar
    Commented Apr 25, 2017 at 8:21
  • I don't see how it's too technical to be here. (FYI It's also named Electrical Engineering not Electronics Exchange) The question belonging there is also questionable, they usually push questions like these back here.
    – Avamander
    Commented Apr 25, 2017 at 13:27
  • @Code Gorilla Thanks for the edit and advice, I'll try Electronic Exchange too.
    – john smith
    Commented Apr 26, 2017 at 3:55
  • SDsolar, Avamander Thanks for showing interest in my post.
    – john smith
    Commented Apr 26, 2017 at 3:57
  • @CodeGorilla I'm well aware of that. It just won't survive there and if you find it off-topic, use the close flags to indicate that.
    – Avamander
    Commented Apr 27, 2017 at 11:08

2 Answers 2


A similar question has been asked in the Electrical Engineering Stack Exchange: EMI/ESD protection for USB interface?

As for the SHIELD connection, you are correct - it is the metal casing of the connector and the braided shield of the USB cable that connects so it, which is likely referenced to protective Earth somewhere on the PC side of things. For EMI reasons it should not be directly tied to the GND signal connection, but should be connected through some impedance. I've seen both parallel resistor / capacitor (as you've shown) and ferrite bead connections between them. --Adam Lawrence

A good technical explanation was written by Ali Chen in his answer to this question:

Ali Chen's Answer to Structure of a USB 2.0 connector

In the answer, Ali recommends using a 330 ohm resistor in parallel to a 0.1uF capacitor between the digital ground and the protective earth (shield).


simulate this circuit – Schematic created using CircuitLab


If the supply for the Shield is 5V, then you can use one of the 5V lines on the Arduino to power the Shield, plus a common ground of course.

  • This isn't about Arduino shields, please read my question again. But thanks for trying to be helpful.
    – john smith
    Commented Apr 26, 2017 at 3:59
  • No probs, but upon reading your question again, to me it doesn't make sense. I am not clear on what you're asking, John!
    – John
    Commented Apr 26, 2017 at 11:21
  • Thanks for the comment. The shield I'm talking about here is the shield of the USB socket (a metallic cover surrounds the female USB connector) which I'm going to use at the 5v power supply side (as its output socket).
    – john smith
    Commented Apr 27, 2017 at 4:36
  • Aha, I think what caused the confusion is the use of the word 'shield'. You're probably aware that 'shields', in the Arduino sense, are accompanying boards that sometimes fit atop the Arduino and provide additional functionality.
    – John
    Commented Apr 27, 2017 at 7:49
  • Read My First Comment!
    – john smith
    Commented Apr 27, 2017 at 15:07

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