Cytron Technical Forum

Can we connect the USB cable and and External 12V supply to the main board together? It seems shorting my USB when I connect it in such a way.

I don have Mega, but I have UNO, get it during crazy sales

Anyway I never experience shorting the USB even with or without the power from adapter. Try putting the adapter only, and try with USB only.

What is the condition when you say it is shorted?

Alen.ATLow WROTE:Can we connect the USB cable and and External 12V supply to the main board together? It seems shorting my USB when I connect it in such a way.

So far, if you put external power supply of < 6.6V then you have some problem. Take a look here:

http://arduino.cc/forum/index.php/topic,82046.0.html

My laptop output device blink when my USB cable touching my USB port. this is weird.
Any way, it work fine with either external power supply or USB port.
Notice that USBVCC from the circuits connected to UVCC of ATMEGA 16U2 IC. may be this is the cause of this problem.

I wonder can we improve this by applying forward bias diode to prevent the voltage flow from higher potential to lower potential source of both USB and External Power supply.

Bricking up Mega is not a big pain compare to having out USB port burn up. haha

So, I guess its safer to go with either external or internal supply

]

Alen.ATLow WROTE:I wonder can we improve this by applying forward bias diode to prevent the voltage flow from higher potential to lower potential source of both USB and External Power supply.

Bricking up Mega is not a big pain compare to having out USB port burn up. haha

Its there already If you see the section after the DC Jack in the sch . There is a diode ^^

[attachment=0]ScreenHunter_11 Nov. 15 15.55.png[/attachment

what about USB VCC ?

I guess putting a diode will lower the voltage from USB by 0.3V, though is not much but for ADC application might affect a lot.

I don have the Mega, so can only study schematic