Questions about the Arduino Micro PCB

Question

I'm planning on integrating an Arduino Micro in the circuit of a small project of mine (USB gamepad). The whole thing will use USB for power and data transfer (between the board and the computer). Before I move on with prototyping, I need to clear up some questions I have about the Arduino Micro schematic (picture included for reference):

• Since I'll be powering off of USB, I won't the 5 and 3.3 V regulators or the 5 V Selector (top-right in picture). Am I correct?
• For the USB Micro header, does the schematic refer to any particular header (doesn't seem so to me), or will any generic one work? And what are the six pins on the right side (SH1/S1, SH2/S2, SH3/S3, SH4/S4, SH5/S5, SH6/S6)? What do they do? What are they used for? I found the pins on the left (VBUS, D-, D+, ID, GND) on generic USB Micro headers, but I did not find the pins on the right.
• Out of curiosity, what do the asterisks in the schematic mean? You can see them all over; for example, look at the top-right of the MCU.
• What do the circle and the smaller circle (with an X through it) towards the bottom-right mean?

Answer 1

The 5V regulator is only used when you are powering from external power (>5V). The 3.3V regulator is only used by things that you power from the 3.3V pin on the Micro.

So if you aren't using external power you don't need the 5V regulator. If you aren't using any 3.3V devices then you don't need the 3.3V regulator.

You can use any micro USB or even mini USB connector you like. If you ignore the "ID" pin you can even use an old-fashioned chunky USB B connector like on the Uno.

The circles are fiducial markers and are special patterns on the board used for aligning a pick-and-place machine when manufacturing.

Answer 2

• “... powering off of USB, I won't [need] the 5 and 3.3 V regulators or the 5 V Selector ...”

True, except that some of those parts maintain circuit continuity. For example, when USB power is used, its current passes through the T1 P-mosfet. For explanation of the power selector circuit, see for example usage of bidirectional mosfet in electronics.stackexchange, or arduino power supply selector at engineeredentropy.com.

In brief, you can leave those parts in place on Micros that you purchase, or could leave them out (while connecting VUSB and +5V) if you replicate the rest of the circuit.

• “For the USB Micro header, does the schematic refer to any particular header (doesn't seem so to me), or will any generic one work? And what are the six pins on the right side (SH1/S1, SH2/S2, SH3/S3, SH4/S4, SH5/S5, SH6/S6)?”

Various generics should work ok, even if they don't have all the SHx shell ground pins shown.

• “... what do the asterisks in the schematic mean?”

The asterisks next to PB7, PB6, etc., designate pins with timer-driven PWM capability.

• “What do the circle and the smaller circle (with an X through it) towards the bottom-right mean?”

That's not clear to me. While they look like fiducial markers, such markers typically are not needed on a schematic diagram. Fiducial markers may be needed on PCBs or PCB layouts, but serve no obvious purpose on the schematic. These may be a designer's idiosyncracy or left-overs.

Answer 3

Let's keep it simple. If you are using USB to power it all, connect the power supply to 5V. The 5V regulator is used to regulate the VIN voltage. The 3.3V regulator is only used to power the 3.3V pin.

USB micro is a type of header. Any common USB micro that you get from a local supplier of EBAY/AMAZON will work.

The asterix and the circle with and without the X are problably markers used by Arduino in there schematic. Don't worry about them.