This is a theoretical situation - for now!
If I have a LED string of some 30 leds which draws more current than one pin of a ProMini is rated for, but less than the current that the ProMini can supply across multiple pins, what would the result of connecting multiple output pins as per the attached sketch? And yes, I do know that the leds are the wrong way round! Please flip them in your mind!!
All the pins would have to be switched simultaneously of course.
No. Use a MOSFET driver. (You can leave-out the diode since you have a non-inductive load.)
You would destroy the ProMini.
Do you know why?
In theory you can do this. But why? You can easily split the LEDs between the pins (i.e. 6 LEDs per pin). It will be safer (no risk of burned pins in case of a bug) and gives you more options - later you may decide to turn on only one group of the LEDs. OTOH I see no advantage of connecting the pins together as shown - unless you need to drive some ready made module that cannot be modified.
Of course using a simple MOSFET (or BJT if you prefer THT components) seems much simpler.
I'm assuming shorting pins together is a bad idea- even if they're all at the same potential?
I don't yet have the module, and have no information yet as to its construction (its being supplied to me by a third party). I'm just throwing ideas up in the air at the moment. I'm hoping that the led string can be split.
Yes but that's only half of it.
You can connect 100 LEDs to one pin, provided that the total current draw is less than 20mA.
The problem is that they may not be at the same potential. You would need to use direct port control to switch all pins simultaneously, and even with that there is no guarantee that the outputs will switch within fractions of a nanosecond of each other. Using digitalWrite will definitely destroy the outputs.
Why not get that power from the 5V pin and use IO pins and transistors to switch leds ON/OFF?
Oh... wait... Arduino board is limited to 200 mA total.
What you want is power external to the Arduino board.
That is actually a very good and accurate explanation of how the I/Os work.
I bookmarked it.
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