Can someone please explain why/if there is a legitimate requirement to connect the arduino/teensy to the same power supply as WS2812B LEDs?
Why is the following not a possibility?
End result should be something close to this. I realise i am connecting the voltage at the far end. This is for a reason and i don't see any issue with this unless the strips have some extra diodes in them to prevent reverse voltage...
Also i have left the capacitor on the LED voltage lines out in these diagrams buy i know there should be one there.
One is that if at any time the Arduino is powered and the strip not, you are driving the strip with data which will attempt to "phantom power" it by the protection diode in the first LED. This is one of the reasons why you have that 330 Ohm resistor, to limit the current in that diode.
The other is that if the strip is more than half a metre long, the foils in the strip cannot adequately carry the full current when most or all LEDs are activated and you need to tap power into the strip at both ends and every metre along its length.
Of course, it is fundamental to comprehension of electrical circuits, that a "circuit" is complete with two wires between the parts so you need the ground connection between the strip and the Arduino and you need the ground as well as the 5 V supply to feed power into the strip at each of the points mentioned above.
Finally, the ground and power, or ground and data wires must not be separate. They must always travel together as a pair - or as a triple - from one part to another and the power wires distributing power to the strip, beside it.
One is that if at any time the Arduino is powered and the strip not, you are driving the strip with data which will attempt to "phantom power" it by the protection diode in the first LED. This is one of the reasons why you have that 330 Ohm resistor, to limit the current in that diode.
The other is that if the strip is more than half a metre long, the foils in the strip cannot adequately carry the full current when most or all LEDs are activated and you need to tap power into the strip at both ends and every metre along its length.
Of course, it is fundamental to comprehension of electrical circuits, that a "circuit" is complete with two wires between the parts so you need the ground connection between the strip and the Arduino and you need the ground as well as the 5 V supply to feed power into the strip at each of the points mentioned above.
Finally, the ground and power, or ground and data wires must not be separate. They must always travel together as a pair - or as a triple - from one part to another and the power wires distributing power to the strip, beside it.
good that i read this, I'm currently powering just a few leds from the usb power of the arduino.
I want to connect a lot of leds and use my psu to give the 5v to power it all.
but wen powering down the pc the usb power will stay's on but the psu power for the leds go of.
in ass you say will damage the adruino true phantom power.
so thinking I can try to connect the 5v from the ardiuno also to the 5v of the leds,
but then the leds will stay on and never turn of and draw all the current via usb.
I don't like disabling USB Power Saving Mode because i still like to charge my headset and such wen turning of my pv
Now of course the NeoPixels always retain the last data sent while ever powered, so turning off the Arduino while the LEDs are powered will not turn them off. And they draw 2 mA per LED even when dark.
Powering the Arduino with the same power supply as the LEDs makes eminent sense. The only concern is "back-powering" the USB port of the PC; I doubt this is a major problem as most "powered" USB hubs do exactly that, but you could cut the 5 V line in a USB cable for this purpose.
Paul__B:
Now of course the NeoPixels always retain the last data sent while ever powered, so turning off the Arduino while the LEDs are powered will not turn them off. And they draw 2 mA per LED even when dark.
Powering the Arduino with the same power supply as the LEDs makes eminent sense. The only concern is "back-powering" the USB port of the PC; I doubt this is a major problem as most "powered" USB hubs do exactly that, but you could cut the 5 V line in a USB cable for this purpose.
That is a easy and simple solution I love it thx.
I've got a eclectic degree en was thinking solutions ass adding a MOSFET to cut of the power line of the usb, wen it get no power from the lpower.
I was also thinking about back powering and what will happen.
the power of the usb would go back thru the 5v power line of the psu powering every thing that might be on that line.
It might even flow back into the psu come out of a other connector on the 5v line that is for instance a HDD or something,
powering that up,
or even damaging it because the hdd is missing on the moment the 12v,
But that might be something that can be different by each power connector of the psu because not all 5v's are parallel and have there own line.
This is something interesting that I going to do some research on, or even try out on a old psu and measure if it can back power 5v on other connectors.
The problem of "back-powering" has nothing to do with any form of overloading the PSU of the PC or laptop, that will not happen (as below).
It is purely to do with the USB port controller device which itself is intended to limit the current provided out of the USB port and has been suggested - in some cases, mostly laptops - to be irreversibly damaged by current fed in the other direction. As I say, this would be an extremely unusual situation, but is routinely noted as a point of concern.
The UNO contains a "polyswitch" which will shut down in time depending on the degree of overload with a current over 500 mA. This is intended to limit current passing from the USB port to the "5V" pin but will certainly act in the other direction just as effectively. The Nano has a diode which unfortunately introduces a voltage drop (depending on what type of diode is actually fitted) but completely prevents "back-feeding" of the USB port.
I don't think or say, that a psu will damage from 5volt going back into it from the USB wen the psu is of.
I do get get that into a USB it can be bad.
It's just wen 5volt is going into the psu it can come back out on a other connector.
But since you say that can at most only be 500mA then I think not much can happen.
Thx for the info this is very interesting to know.
