Multiple leds on ONE PWM pin

I have arduino nano (because of its size I cant use anything bigger) and I noticed there is a problem when I try to turn on (just once at the begining) more then one LED (with fade in brightness) on the same pin. There are only 6 PWM pins if Iam correct (3, 5, 6, 9, 10 and 11) and I have several LED boards and I would like to turn them on gradually and gradually increase the intensity (fade in) of the LEDS on those boards.

So for example I have 3 boards (each has 8 SMD LEDs) and I would like to turn them on (with the fade in) all at once then wait a second or so and do the same with another 3 boards (each has 5 SMD LEDs) and then again wait a second or so and then turn on next 3 LEDs ....

Iam ablbe to do it when I connect the boards to individual pins (like one board to pin 9, second boapr to pin 6 ....) but because there ale only 6 PWM pins I wouldnt be able to turn on all boards and leds unless I would be able to somehopw connect them to one pin. Is that possible? It seems the pin has limited power supply because when I connect two boards on one pin only 6 LEDs from total 16 are lighted :((

You can run multiple MAX7219s in series off the same pins, but it takes a couple. They will drive the LEDs and allow you to adjust the brightness of each LED group by themselves.
They are powered separately and the Arduino pins are just used for serial coms, not to provide power.

"I have 3 boards (each has 8 SMD LEDs)"
What kind of board?
What kind of LEDs are used on the boards?
How are these LEDs connected, in series or in parallel?
How are you going to connect them to the Arduino?
The atmega328 output pins support a maximum of 20 mA.

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RV mineirin

If you have any LED boards that draw more than 20 mA or which run at a voltage greater than 5V you can use a small NPN transistor to act as a switch between the Negative/Cathode/Ground side of the LED board and the power-supply Negative/Ground terminal. The Arduino PWM pin can then turn the transistor on and off to control the higher current or voltage.

  • Its custom board just for LEDs, nothing special there, the LEDs are just placed on exact spots to match some buildings in a model KIT
  • 5050 LEDs are used, warm white, blue and yellow. The warm white and blue are almost the same values (60 mA and 3,3 or 3,2 V) the yellow is 20 mA and 2,2 V. One board has 3 x warm white LEDs, 3 x yellow LEDs and 2 x blue LEDs = 8 LEDs total
  • LEDS are in paralel
  • I just wanted to connect them to some pin and GND which works, but I have to connect one board to one pin. If i try to connect two of those boards to one same pin (lets say pin 9) only the yellow LEDS on both bords are lighted, the blue are just bearly visible and the warm white LEDs are probably not lighted at all - no visible light.

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