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8 years ago.
Can I use external power supply and USB at the same time?
Hi, I'm using an STM32 Nucleo F446RE. I have to read many times per day some value from an analog input. I want to use an external power supply and than use a USB cable to read this vale (that I put into an array in ram) on the pc using the USART (I use the serial comunication to send all the value when I press the button). My question is, if I use a 9V battery on the pin Vin (JP5 on the external pin) and at some point I connect the PC to the board, there is some probroblem whit power supply? With JP5 switched, teorically, there are no problem with 5V of the usb and 9V of the battery, but GND? they will be shorted? (I've not test it, because I'm afraid of this)
PS: Otherwise, someone know how to save the array in the flash memory, so I can even unplug the power and than use the sub cable with the PC?
Thank's.
1 Answer
8 years ago.
There is no problem with what you propose, TP5 in E5V position, external power to the 446. Yes the grounds will be connected together when you plug in your PC to the ST-Link part, but that is normal.
There are 20 x 32bit RTC backup registers & 4KB of backup SRAM on the 446, but you will need to add a coin-cell battery to Vbat and remove a zero Ohm resistor at SB45 to make use of those. Like this: https://developer.mbed.org/users/gregeric/notebook/battery-backup-for-rtc-clock--registers-on-stm32-n/