I'm using UNO for a project and unfortunately I couldn't connect a power supply to it. So I simply use USB to power it from a laptop. It works fine most of time. However in some cases when I have too many USB devices (10+) connected to the PC via a HUB, I found my Arduino board didn't work well sometimes. I measured its USB port voltage and it's only about 4.68V (and 0.04A). I believe it's way too low from the expected 5V. Does anyone happen to know what Arduino UNO's functional voltage requirement?
I also have a Arduino DUE which has a similar issue. My DUE also doesn't have a dedicated power supply. It gets power via USB cable. Would appreciate if anyone can tell me its voltage requirement as well.
I measured its USB port voltage and it's only about 4.68V (and 0.04A). I believe it's way too low from the expected 5V. Does anyone happen to know what Arduino UNO's functional voltage requirement?
That's not even 10% low and I think you'll be fine. The ATmega chip can go down to 1.8V, but IIRC, it also depends on the clock frequency and of course there are other chips on the board. And it also depends on the requirements of whatever you are interfacing it with.
...Powering 10 things from a USB hub seems kind of "crazy".
I also have a Arduino DUE which has a similar issue. My DUE also doesn't have a dedicated power supply. It gets power via USB cable. Would appreciate if anyone can tell me its voltage requirement as well.
The Due runs from 3.3V so I guess it has a regulator for 5V USB power. The regulator will "drop out" if the voltage gets too low but I'd expect it to work with less than 4V into the USB port. The USB port also expects ~5V signals, so it may fail if the voltage gets too low, even if the processor is still happily running.
Uno will work at 16 MHz and be fully in spec with Vcc down to ~3.8V.
If you're using analogRead, that will also be the upper limit of voltages to read, and any input pins need to be <=4.3V.
Any high outputs will be <=3.8V, and maybe 0.4 to 0.5V below that if heavily loaded.
There is another thing to consider here. Although Doug already mentioned that powering 10 devices from an USB hub is crazy, most computers also have protections in place for their USB ports. The current is limited to 500mA, if your consumption is fluctuating around that point the power will be turned on-off pretty fast, influencing the power your Arduino gets. Better (read more expensive) computers also have a thermal protection on their USB ports, those normally cut the power for a longer time, until their thermal drops below a certain point. I really would advice you to acquire a dedicated power supply for your Arduino's
thanks Doug and Mike! It's kind of interesting that after I moved Uno to connect to the PC directly then it becomes much more stable. According to your folks' reply, voltage shall not be the concern here. Will current be the issue? I heard USB hub is notorious famous for its inconsistent power (voltage/current) supply, particular when PC is at the peak of computing (100% CPU/GPU). I saw clearly voltage/current fluctuating a lot. Does UNO have its own regulator?
Better (read more expensive) computers also have a thermal protection on their USB ports, those normally cut the power for a longer time, until their thermal drops below a certain point.
Interesting. We probably shall check it out.
