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Topic: leds And resistors (Read 1 time) previous topic - next topic

GreyArea

Referring to groundfungus' Diagram...

Is it okay to take power for the neopixels from the +5v and GND terminals of the Trinket, with the Trinket powered by USB?

If so, the power and GND would enter from the same "end" as the data. I know Adafruit recommend having the resistor as near to the pixels, not the controller...does it matter where the capacitor is sited in the same fashion?

Once again, thanks.

groundFungus

#31
Feb 05, 2018, 08:44 pm Last Edit: Feb 05, 2018, 08:45 pm by groundFungus
You can power the LEDs from the Trinket as long as you are very careful to not draw too much current (< about 500mA total for USB).

Actually the location of the resistor is not that important.  The cap should be as near the strip power input as possible for the least wiring voltage drop.  It doesn't matter which end the power is fed to the strip.  You can feed power to both ends.  If you have long strips you can inject power in the middle and both ends.

GreyArea

Did a bit of reading. A dedicated charging USB port is rated at 1500mA, the power packs I have are I believe 1200mA (I may be confusing mA and mAh though, will check tomorrow).

If the above info is right, would it be better to wire the LEDs and the Arduino directly from the powerpack, rather than take the LEDs from the +5v on the Arduino, i.e. as per your original diagram?

GreyArea

If i do inject power at more intervals, does each connection require the capacitor?

GreyArea

But you should never turn off the power to a string of WS2812s when the data pin is connected up anyway or you will damage them.
Regarding the above...is there a way to turn off the LEDs safely? I'd rather they weren't on all the time...

TomGeorge

Hi,
Regarding the above...is there a way to turn off the LEDs safely? I'd rather they weren't on all the time...
If you need the controller to be still operating, then get it to command all the LEDs to turn OFF.
Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

groundFungus

#36
Feb 06, 2018, 12:23 am Last Edit: Feb 06, 2018, 12:39 am by groundFungus
Where in the diagram did I indicate that the 5V strip supply is from the Arduino 5V?  I certainly did not mean that as the strips that I use are all powered by an external 5V supply.  USB 2.0 ports can supply 500mA, USB 3.0 can supply 900mA, a charging port can supply more.  As to the 5V regulator, it depends on the amplitude of the source of the supply voltage to the regulator how much current the regulator on an  Arduino can supply.  The more voltage that the regulator must drop, the less current the regulator can supply before it overheats.   For instance, on an Uno the regulator can handle about 1W of power dissipation.  With a 12V supply that means that the regulator can not supply more than about 150mA to stay under 1W dissipation.  With 7.5V to the regulator about 400mA.

I would distribute the capacitance between the taps.  Divide the 1000uf by the number of taps and use the closest standard value at each tap, as close to the strip as possible.  But no lower than 100uf on each.

GreyArea

Where in the diagram did I indicate that the 5V strip supply is from the Arduino 5V?
You didn't. I worded my statement poorly. Please see below with added parentheses to try and clarify, sorry.

"If the above info is right, would it be better to wire the LEDs and the Arduino directly from the powerpack, (rather than take the LEDs from the +5v on the Arduino) i.e. as per your original diagram?"

Or to be perfectly clear;


"If the above info is right, would it be better to wire the LEDs and the Arduino directly from the powerpack, (...), i.e. as per your original diagram?"

Hi,If you need the controller to be still operating, then get it to command all the LEDs to turn OFF.
Tom... :)
So, if I have a power switch that kills power to BOTH the Arduino and the LEDs, that's okay? Or if I do power from usb, with +5v and GND from the Trinket to the LEDs, just pulling the USB cable out doesn't risk harm?


groundFungus

Take the power for the LEDs from the power pack, not the Arduino 5V.

GreyArea

#39
Feb 06, 2018, 11:48 am Last Edit: Feb 06, 2018, 11:53 am by GreyArea
Take the power for the LEDs from the power pack, not the Arduino 5V.
+1 Karma for clarity!

Is the attached diagram a correct interpretation of what you've all told me so far?

The power packs I have are rated at 1.0A output and are 1200mAh. Adafruits guidance is to assume 20mA per LED, so absolute maximum would be 50, but in practice my animations run maybe 10 to 20 at a time and only at a maximum brightness of 100 (not 255), so hopefully I am covered.

TomGeorge

Hi,
OPs diagram;


Yup, that looks good.

Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

GreyArea

Bah. bought a pack of capacitors of varying sizes thinking the one I need would be in there...

10pF to 220nF...that would be a "no" then...

Just confirming, 1000nF = 1µF, 1000µF = 1mF, yes? so I'm about a factor of 5,000 low?

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