Is it possible/safe to solder wires to the underside of the USB Jack on Arduino Mega 2560, and connect to a regulated 5v supply?
You can also add it to the 5V pin, if you add a diode between the 5V and VIN with the anode on the 5V.
Otherwise, I believe you can safely solder it to the +5V and GND pins of the USB input. Assuming you do a good job, and strain relieve it somehow (so that pulling on the wires won't tug at the solder joint, I suggest hot glue) you should be fine. However, I would never try plugging in the 5V and USB in at the same time. You could possibly damage your computer that way.
Probably better to cut the USB-A end (the PC end) off of a cable and connect that to your supply - leave the USB-B end alone.
Otherwise, yes you can.
CrossRoads:
Probably better to cut the USB-A end (the PC end) off of a cable and connect that to your supply - leave the USB-B end alone.
Otherwise, yes you can.
I was going to do this, but space requirement are tight, and the enclosure needs to be water tight, so i thought itd be neater to just take wires from the jack underside to my 5v supply rail.
So just to make sure, if i want to connect the 5v rail to the 5v pin on the board, i just have to connect a normal diode between the Vin and 5v ports? This will not cause any drop on the output voltage of digital pins?
Made a little diagram to confirm
Yes. The diode prevents the 5V from reverse driving the 5V regulator and damaging it.
The '328P will be powered from 5V, the IO pins will act normally.
CrossRoads:
Yes. The diode prevents the 5V from reverse driving the 5V regulator and damaging it.
The '328P will be powered from 5V, the IO pins will act normally.
Yep, actually I think it was Crossroads that showed me that trick.
Just reading the regulator data sheet.
If you bring power to the 5V pin, you also bypass the USB 500mA resettable fuse, which has a finite resistance and causes some voltage drop.