hi guys,
I use arduino uno for controlling and monitoring temperature for refrigeration system, and the arduino connected to the 12VDC power supply via VIN pin, and I want to connect the arduino with PLX daq to send temperature data who connect with USB PC. I know that USB supply 5VDC to the arduino. is there anything problem with arduino when I connect the USB and it supplied with 12VDC via VIN pin?
thanks
best regards,
asmoro
You can connect the UNO to USB and apply power to the power jack at the same time.
One would hope , right ? (being as they are both on the same board...)
LarryD:
You can connect the UNO to USB and apply power to the power jack at the same time.
I don't quite understand what the OP is doing, but your comment caught my eye. I've had the AC adapter plugged into my Uno while I'm programming via the USB port before. It seems to run OK. I'm not sure where the Uno is getting it's 5V - from the AC adapter or the USB bus? Am I not suppose to do this? Is the 5V from the USB bus fighting the 5V from the AC adapter?
From the wall wart unless it is unplugged, then the USB will power the Arduino.
see attached schematic
arduino-uno-schematic.pdf (32.7 KB)
perhaps you can help me, if i am right with the scematics?!?
the part of the schematic, wich i have attached, is used for the power-supply. and no matter what is connected (usb, v_in, ...) the lp2985 handles everything and gives constant 3,3V output? just to be sure...
Yes but why would you ask that question ?
i am pretty new with electronics and schematics.
just to be sure...
XD
Do you want to know how that circuit works or are you satisfied with the answer you got ?
...) the lp2985 handles everything and gives constant 3,3V output
+5V comes from USB via the P channel MOS FET OR the 5 volt regulator, U1 ( which is connected to Vin/wall wart).
The 5 volts goes to the 2985 and it outputs 3.3V (and it powers the comparator).
If you have a wall wart pulled in, Vin effectively turns off the FET via the comparator U5, therefore the UNO is powered from the wall wart.
If you unplug the wall wart the comparator turns on the FET and USB powers the UNO.
I can't tell you how the circuit works unless you ask because I have been cautioned not to volunteer technical information unless it is requested to a newbie because their brain might explode..
It's my fault :*
thanks for assistance,, 
