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Topic: Disable USB Power on Mega 2560 R3 (Read 2695 times) previous topic - next topic

cfadamnelson

Hello, I need to disable the USB power on the Mega2560 rev 3.  We have it externally supplied, and when our power switch is off I would like the entire system to be dead.

I tried removing F1, but the computer stopped recognising the 2560 in the device manager; I need to be able to communicate with the computer still.

Does anyone know how to properly disable the USB power?  I know there is an auto-change over that will run it off of our supplies, but some LED's and a fan keep running after the switch is thrown as the USB power takes over.  I tried a search, but found no answers.

thanks in advance,

Adam.

CrossRoads

Time to study the schematic some more. I imagine trace cutting is the next step.
Unfortunately I cannot open the schematic without getting logged out of this response, I may be back in a while ;)
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CrossRoads

Or worse, IE times out and I have to restart IE to recover.  Arrrgh.

Ok, if you replace F1, and remove T1, that will remove the USB-VCC path, while allowing the USB/Serial interface to remain powered.

However, Reset is pulled High to 5V, so you will also need to remove RN5 (resistor pack) and D2 and wire in a resistor/diode to bring Reset2 to USBVCC, and put a 10K resistor across pins 1/8 for the 2560 Reset pullup.  The other 2 resistors in the pack are used for autopower switching, which is disabled with the removal of T1, and don't need replacing.

http://arduino.cc/en/uploads/Main/arduino-mega2560_R3-sch.pdf
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Coding Badly


It may work to put the ATmega16U2 into deep sleep if there is no activity for some time.  That would require modifications to the firmware.

cfadamnelson

Hey guys, I got it figured out.  The FTDI needs to be powered by the PC, and the rest of the board by my power supply.  I removed T1 (the 3 pin mosfet just below F1), and it works.

The microcontroller and led's are powered by the power supply, and the FTDI is powered by the PC.  The PC now detects the board, and it programs, guess I just needed to sleep on it.

Thanks for the response though guys!

cfadamnelson

haha, thanks crossRoads, I just read your post, that's exactly it.

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