Sorry, I know it's a frequent kind of question here, but I'm trying to get clear:
I know the 5V pin on the Nano Every is current limited... I hear it's about 800mA, and that it would maybe be foolish to expect even that much.
I will be using a "2A" 5V supply via the mini-USB port. I only need to power 10 LEDs on an addressable LED RGB strip (this one) which states ~60mA per LED.
600mA + some for the arduino seems well under 800mA and well under the 2A power supply... could I get away with powering them from the 5V pin? I know it adds up on paper but I'm not sure what the cold reality is like.
I would like to do this if it's reasonable because it will help me avoid complication in assembly (we're going to be scaling this up to a lot of units, so that matters...)
Thank you -- so I should be fine as long as I'm <= 1A... Some things I had read elsewhere in the forum made it sound like that current wasn't necessarily all available, but maybe they were only talking about the case when the incoming power was via computer-supplied USB (which I understand). Sounds like I'm good to go.
Side question: say I needed more than 1A. I'm using a 2A 5V power supply (like this)... The temptation would be to splice into the line, tap the >1A off of it, and plug the mini USB into the arduino as normal. My understanding from the schematic is that the Nano Vusb just goes right to the 5V rail... is there a substantial risk that this wall wart 5V would sag or otherwise be of poor quality in a way that might hurt the board? I know that sometimes the regulation on such supplies is shaky... I guess the better alternative would be to use a higher voltage PSU and go into Vin, but I'd love to stick with a 5V supply if I can (to match the LEDs).
Feed the 5 on the plus 5 line and ignore Vin. the Arduino should SUPPLY no power, It should be FED power on the +5. Don't use the onboard regulator at all.
Thanks @madmark2150 -- which scenario are you referring to? The one where I need more than 1A? You're saying to not use the USB input, but to split the PSU 5V to both the LEDs and the "5V" pin? (I thought that pin was supposed to be used for output and that input via that pin was "not recommended"?)
What is the advantage to doing it that way, as opposed to feeding 5V via the USB input, and supplying power from the PSU to the LEDs? Both ways would avoid the on-board regulator, no?
Feed +5 in on the +5 pin. The +5 PS can also run your IO devices.
I run +5 in and have a switch to break the RED wire in the USB cable. This prevents back feed.
The USB has circuitry between it and the actual +5 that supposedly blocks back feeding. These components reduce the USB voltage somewhat. +5 as an input runs everything at full PS voltage no matter what. Peak current from the PS can be higher too.
A GPIO pin has a max. current limitation:
A GPIO pin driving high (providing the current) or a GPIO pulling low (draining the current) has
always a limitation - see the chip specification/datasheet for the values.
I would assume: 2 mA is OK, max. might be 16 or 32 mA, but for sure not higher!
You have to imagine this:
a) when driving high (a current comes out of pin) - the max. current is limited by the tiny wires
inside the chip: a stronger current will burn your structures (wires) in chip.
And the internal "wires" have a resistance: so, they might limit anyway the current (and create heat). The current has to go from external power supply through the chip to the pin: could you imagine the current can be large? (without ton burn this tiny guy)
b) when level is low and pin draws the current through the chip from outside - it is the same
problem: thin wires with high current, a lot of heat generated in chip, the current has to flow now out via GND - the same tiny wires.
So, almost all MCU chips have two limiting parameters:
how much current can be provided (high) or taken (low) by a single pin, before the internal
components (transistors) are blown up by heat?
the total heat generation: imagine, you would draw 10 mA on 100 pins: this this 1 A for the entire chip: the chip will potentially not be able to have 1 A on the power feeds.]
It will create so much heat that entire chip gets burned.
==> so, often chips have a specification: how much total current for all GPIO pins can be handled (before it dies due to thermal issues).
And: CMOS logic, used in chips, limits the current anyway. Often you have settings for "Drive Strength" which modifies the internal logic a bit, e.g. lower resistor values, higher voltages.
So, the current a GPIO can drive (or take) depends also on the "Drive Strength" config for this pin. A higher current (often needed for higher frequencies) need a stronger Drive Strength.
GPIO pins and their current have an effect on the power supply (able to provide more current). But potentially it is the chip itself which limits how much current per pin and how many pins per chip can have a high current. Before the Power Supply is overloaded - the chip might be for sure (thermal wise).
CMOS logic actually do not need really a current. Problems happens just with external circuits, e.g. driving LEDs or pulling low on a low resistance external loads (e.g. inductivities, relays, motors).
MCU pins are not designed as "drivers": they might just cover the spec. for TTL signals. When it comes to high current - an external driver is needed. MCU GPIOP pins should not drive or drain so much current (to avoid overheating of the chip).
No, there is still a limit on the 5V DC/DC converter no matter what voltage you feed into it.
Remember that we are talking about a Nano Every here, I think you might have confused this with discussions of a Uno or Nano which is the name most people use, where as a recent name change means they should actually call it as a Nano Classic.
There are always lots of different ways to do what you want.
If you need less than 1A then there is no issue powering via USB and using the 5v output from the Every. The main advantage is that you already have a power supply with a suitable connector.
If you need more than 1A, then you are better off just supplying power to the 5v pin, and to whatever other devices you have directly.
1A out of the reg is optimistic. If you're running at 12V Vin the limit isn't current, but HEAT. With a 12V supply you have 7V being dissipated as heat. 7V x 1A = 7W, that SMD 7805 is going to get HOT and I mean FAST. while the 1A is theoretically possible at 7V, at 12V it ain't going to happen. Those linear 7805's like to fail SHORTED when overheated, placing the full PS into the logic, letting the magic smoke out.
Do yourself and the card a favor and supply clean, solid +5V on the +5 line and share it (separately) with the IO devices. Put a switch in the RED USB wire to isolate when both the +5 AND USB are connected.
We are not talking about Nano ( classic ) but Nano Every. The Every contains a completely different voltage regulator (MPM3610), which is an integrated buck converter.
One part that is still confusing is the powering via the 5V pin. E.g. these docs say that powering via 5V pin without any other power source can damage the regulator: "Since 3V3 and 5V pins are directly connected to the onboard's 3V3 and 5V voltage regulators outputs, these pins have no reverse polarity protection. ... it is not recommended if no power supply is connected through the USB port, the barrel jack connector, or the VIN pin. ... Suppose the voltage in the voltage regulator output pin becomes higher than the input voltage of the voltage regulator. In that case, a large current may flow into the voltage regulator from its output pin to its input pin. That large current can permanently damage your board's voltage regulator."
Doesn't that contradict the idea that I could safely supply via the 5V pin? That paragraph makes it sound like the inline switch @madmark2150 mentioned above would actually be a bad idea?
I'm also curious to know how safe/reliable your average cheap wall wart PSU is. I was going to get this, and if I supply the 5V pin directly with what is supposed to be a "regulated" supply, I wonder about voltage sag and so forth if there are other loads on the PSU. In other words, does your standard cheapo PSU really qualify as a "regulated" supply input, and could damage happen if the voltage drops?
Yeah I will do that if I need more than 1A. For less than 1A, the reason is just simplicity in assembly for when we scale this up to 40+ units.
