Hello everybody!
for a project I'm working on I want to control individually the brightness 12 RGB LED strips, for example turning on one at a time in a given order. When the LEDs are not on they should be actually half brightness, so I think I have to exclude the use of relays and go with transistors.
I also need to control their color, but that needs to be the same for all of them, so it seems more efficent/elegant/clean to me to use 3 transistors/pins on the arduino for the RGB values and 12 for the brightness(es), rather than using 12 + 3 = 36 transistors.
Is it possible to control with just 3 transistors on the RGB lines of the LEDS and then have another transistor on each + line of the LEDS, or that would create problems?
Of course picking transistors with the appropriate power rating.
If it's not clear I'll try to make a schematic.
I have some experience about Arduino programming, but when it comes to electronics I'm always afraid to make a giant mess 
Thank you everyone
andreaefferao:
Hello everybody!
for a project I'm working on I want to control individually the brightness 12 RGB LED strips, for example turning on one at a time in a given order. When the LEDs are not on they should be actually half brightness, so I think I have to exclude the use of relays and go with transistors.
I also need to control their color, but that needs to be the same for all of them, so it seems more efficent/elegant/clean to me to use 3 transistors/pins on the arduino for the RGB values and 12 for the brightness(es), rather than using 12 + 3 = 36 transistors.
Is it possible to control with just 3 transistors on the RGB lines of the LEDS and then have another transistor on each + line of the LEDS, or that would create problems?
Of course picking transistors with the appropriate power rating.
If it's not clear I'll try to make a schematic.
I have some experience about Arduino programming, but when it comes to electronics I'm always afraid to make a giant mess
Thank you everyone
RE: Is it possible to control with just 3 transistors on the RGB lines of the LEDS and then have another transistor on each + line of the LEDS, or that would create problems?
If it's not clear I'll try to make a schematic.
You are correct , you will need to draw a schematic.
Not just for us, but for yourself.
LED Shield
MOSFET
So you'll have say P-channel MOSFET sourcing current to the + pin, and 3 N-channel MOSFET sinking current from the 3 - pins, with PWM going on both ends, + for brightness and - for color mixing?
Could work I suppose, may get odd flickering on something from the 2 PWMs interacting with each other.
I think that would be less likely if you just reduced the N-channel PWM level by 1/3 or 1/2 or whatever appears most pleasing when you want it dimmer.
Easy enough to try - set up 3 strips with 3 transistors and see how it looks.
AOI514 from digikey works well. I have 32 of them on a board for driving LED strips:
http://www.crossroadsfencing.com/BobuinoRev17/
Here's a clip with 8 LED strips fading up & down.
Can use shiftPWM library to control LED colors,
http://www.elcojacobs.com/shiftpwm/
and add PWM to 74HC595 OE/ for overall brightness too.
