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Topic: Arduino Mega 2560 R3 Power readings (Read 5527 times) previous topic - next topic

Paul__B

it will draw a small current because there is a resistive divider across the output pin
And not only that resistive divider, but also the current mirror to the left of it.

theace

And not only that resistive divider, but also the current mirror to the left of it.

In that case, I can remove the 5V regulator. It's easy.

dwightthinker

You might also remove the power LED. It might be
more than you think.
Dwight

theace

That also, no problem.

The USB chip is my problem.

dwightthinker

If it has the 8U2 chip, I suspect it has a power down
mode.
It would require rewriting its firmware and reprogramming.
Sounds like an interesting project.
Dwight
 

theace

I want to be able to still use it ONLY when the usb cable is plugged.

dwightthinker

I don't think putting the USB chip in powered down would stop
power to the rest of the board?
Dwight

CrossRoads

If the Rx/Tx LEDs are powered, then current can flow thru them into the USB chip via the IO clamp diodes, and the USB chip could act like it was "phantom powered". Same with the Rx/Tx pins connecting to Tx/Rx on the uC.  And the Reset pin.

The USB chip in powerdown sleep mode should not impact the rest of the board, as long as the Rx/Tx pins are set to INPUT before going into sleep mode.
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

Quote
I want to be able to still use it ONLY when the usb cable is plugged.
So remove the 5V regulator? Then power can't get in via the barrel jack even if a power cable is plugged in.
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.

theace

#24
Sep 24, 2015, 11:17 pm Last Edit: Sep 25, 2015, 01:18 pm by theace
I don't need the barrel jack or VIN. I will only provide power through the 5V pin.
As for the USB chip, I don't want to change its firmware because I need it for programming. I only need it to not be powered when an USB cable is not plugged. This is why I asked if interrupting the VCC line (pin 4 on ATMega16U) as described in the previous picture would suffice.

Edit: I have looked again through the schematics and realized that a good way to disable ATMega16U2 when the USB cable is not inserted is to cut the current connections of pins 4 (VCC) and 32 (AVCC) of ATMega16U2 and rewire them to the USBVCC. This way, the USB chip is only powered when the cable is inserted and will function normally.

Is this a good and better approach?

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