Couldn't find an existing thread that answers my question, so here goes.
I'm working on a project where I'm powering an Arduino UNO through the USB-B port. I also have some surrounding electronics which I power from the Arduino's 5V pin. I've understood that I can safely draw around 450 mA from the 5V pin in this scenario (500 mA according to USB standard - a few mA for the Arduino itself).
However, at this moment the Arduino is built into a PC, and powered through a spliced USB cable connected to the ATX PSU's regulated 5V standby rail.(Yes, I have confirmed the voltage to be stable) The standby rail can supply more than the 500 mA of a normal USB port. Am I still limited by the ~450 mA limit on the 5V pin or could I draw a bit more in this case? At what point is the current limited by the components and traces on the Arduino instead of the capability of an USB port?
Bonus question: Anything I need to consider if I intend to run the Arduino 24/7 concerning longevity? (lower levels of power draw from 5V line about half of the time, with occasional peaks)
An Arduino hardly can consume 500mA without releasing the magic smoke. If you have more power hungry modules around it (motors...), you need driver modules which can connect directly to the PC power supply.
If you are indeed using a UNO, then it has a 500 mA polyfuse in series with the USB power.
Bonus answer - the Arduino has the same durability as your PC - arguably better (fewer components).
(It worries me that people use UNOs for serious projects - Nanos are more compact, easier to connect to and cheaper for virtually the same functionality! And for the same question, the Nano may be limited by a diode between the USB connector and the 5 V pin.)
Thanks for the answer Paul__B! Guess I'll make a separate power circuit if I need more current.
Also, good tip regarding the Nano, might rebuild it out of one of those later when the project is finished to make it a bit neater! (Although noone sees it inside the PC :D)
I went with the UNO mostly because I'm using an USB host shield and wasn't sure if the libraries support Nano pinouts directly. Also most of the documentation/forumposts about this stuff is about UNOs which is a plus since this is my first real project.
Tuners22:
I went with the UNO mostly because I'm using a USB host shield
What for?
Apart from the USB interface chip and the identity of the bootloader, the Nano is programmatically identical to the UNO, so it is only a matter of connections.
Apart from the USB interface chip and the identity of the bootloader, the Nano is programmatically identical to the UNO, so it is only a matter of connections.
It's easier to mount USB Host shield on Arduino UNO, if you have to connect it with Nano then you will need to do a little soldering, it will be difficult task. I think you should keep using Arduino UNO with USB Host Shield.
Paul__B:
I was looking for an answer to my question as asked - for what did he need a USB host shield?
I'm reading an USB receiver for a 2.4GHz RF remote control (originally intended for some smart TV box I think, so normal multimedia buttons), so I can use it to turn on/off the PC. I also got some IR blasters connected to the Arduino so I can control a TV and a stereo which are connected to the PC with the same remote.
Next step is to integrate some of the living room mood light on the same remote After that I will be out of buttons, sadly.
I realize there's universal remotes to buy, but where's the fun in that!
And for the same question, the Nano may be limited by a diode between the USB connector and the 5 V pin.)
After that I will be out of buttons, sadly.