When you’re controlling RGB LEDs traditionally using PWM on each channel, you need something like an and-gate to power the power the lights. Otherwise, you’d be powering the leds directly from the ouput pin of the microcontroller.
What do you use to make that work? It has to switch quickly enough to move at the same rate as the PWM.
So this doesn’t apply to the individually addressable strips we mostly discuss around here.
But, that said, lots of people trying to drive high current LEDs or analog LED strips use MOSFETs. Try googling for “arduino mosfet led dimmer” for circuit diagrams and tutorials.
Thanks, I know it doesn’t really apply to FastSPI_LED, but I’m helping a friend with a project. Unfortunately they made some old-school design decisions.
Yep, I get it. Also, sometimes one-color-for-all-pixels is all you need for some things, and given the price difference ($/lumen), there’s still plenty of use for these designs.
I’ve used MOSFETs to do this myself. It’s a pretty easy, “cookbook” sort of circuit.
I’ve also used a BlinkM MaxM to do the same thing, but with I2C control over the RGB color instead of built in Arduino PWM. Don’t ask me why I went this complicated route; I forget, and sort of fear what I’d find if I did someday remember.
Here are a few of the many writeups on driving strips like that:
I have used these schematics for my own Analog RGB strip projects:
http://dl.dropboxusercontent.com/u/10830255/Arduino%20RGB%20on-beat%20leds%20Project/Scematics%20on-beat%20RGB%20strip.pdf
Jon: shouldn’t there be pull-down (or up) connections in there between the Arduino and the power transistors? The 220 ohm resistors look oddly arranged to me, but I’m not an expert in this so please enlighten me if I’m off base.
No pull-anything needed. The series resistor is controlling current to the transistor or mosfet. That’s all you need to turn it on/off. The thing to watch out for is how fast you can flip the transistor/mosfet. They’re not all made for high speed switching …
Ah right, since the output is either high or low, not floating. N/M
Yep, the IRL520 is fast switching, rated at 100v, and 9.2 amp drain. Pretty beefy little guys I’d say