Arduino Nano USB connection with external power

I've decided to use 12V power supply in my project, however, Arduino needs to be connected to PC aswell. What is the procedure for this? It is a MIDI controller so the board needs to talk with PC. I am planning on connecting +12V into Vin pin and ground into one of GND pins. I guess the USB connection needs only TX/RX then?

kustom: I've decided to use 12V power supply in my project, however, Arduino needs to be connected to PC aswell. What is the procedure for this? It is a MIDI controller so the board needs to talk with PC. I am planning on connecting +12V into Vin pin and ground into one of GND pins. I guess the USB connection needs only TX/RX then?

If you plug them both in, the auto-selector will choose Vin for power. USB communication will work fine. See Below.

[quote author=James C4S link=topic=146538.msg1101058#msg1101058 date=1359827500]

kustom: I've decided to use 12V power supply in my project, however, Arduino needs to be connected to PC aswell. What is the procedure for this? It is a MIDI controller so the board needs to talk with PC. I am planning on connecting +12V into Vin pin and ground into one of GND pins. I guess the USB connection needs only TX/RX then?

If you plug them both in, the auto-selector will choose Vin for power. USB communication will work fine. [/quote]

On a Nano board? I believe a Nano uses simply two diodes for voltage selection, so the higher voltage either from the on-board voltage regulator or the USB +5vdc will be the one supplying the current. No?

Lefty

retrolefty: On a Nano board? I believe a Nano uses simply two diodes for voltage selection, so the higher voltage either from the on-board voltage regulator or the USB +5vdc will be the one supplying the current. No?

You're right, I missed that it was a Nano.

kustom: I've decided to use 12V power supply in my project, however, Arduino needs to be connected to PC aswell.

Will the PC always be connected when in use? If so, there's no reason to run the 12V through the Arduino in the first place.

[quote author=James C4S link=topic=146538.msg1101076#msg1101076 date=1359828074] If so, there's no reason to run the 12V through the Arduino in the first place. [/quote]

It's because I use lot of stuff - 6 4021 registers with 48 button inputs, 4 74HC595 registers with 27 leds, 5 4051 multiplexers with 31 potentiometer and one LM324 comparator to read the data from 2 rotary encoders.

kustom: It's because I use lot of stuff - 6 4021 registers with 48 button inputs, 4 74HC595 registers with 27 leds, 5 4051 multiplexers with 31 potentiometer and one LM324 comparator to read the data from 2 rotary encoders.

Yes again, you don't need to run the 12V through the Arduino. Use a separate voltage regulator to power all of that hardware with 12V. Then let the Arduino be powered by USB. Just make sure to connect your grounds.

How much current are the LEDs going to draw? Even at 20mA each, that's over 500mA. You're going to have a hard time using the on-board regulator to provide that much current, especially with 12V in.

[quote author=James C4S link=topic=146538.msg1101113#msg1101113 date=1359829084]

kustom: It's because I use lot of stuff - 6 4021 registers with 48 button inputs, 4 74HC595 registers with 27 leds, 5 4051 multiplexers with 31 potentiometer and one LM324 comparator to read the data from 2 rotary encoders.

Yes again, you don't need to run the 12V through the Arduino. Use a separate voltage regulator to power all of that hardware with 12V. Then let the Arduino be powered by USB. Just make sure to connect your grounds.[/quote]

Do you mean that I should use lm7805 regulator connected to those 12V?

[quote author=James C4S link=topic=146538.msg1101113#msg1101113 date=1359829084]How much current are the LEDs going to draw? Even at 20mA each, that's over 500mA. You're going to have a hard time using the on-board regulator to provide that much current, especially with 12V in. [/quote]

LEDs need to be very dim so there is 1kOhm resistor on each.