I'd like to be able to programatically control the brightness of a set of 12v leds (not individually, just the brightness of the whole string).
I have a Duemilanove. From what I've read, led brightness is conventionally done with pwm where the output is 5v. How should I go about powering/fading these 12v leds?
I've thought about using a little 12v A23 battery to power the arduino and connecting the leds to VIN and a digital potentiometer. I'm new to the scene so I may be missing something obvious. Let me know what you think!
Sounds like you're looking for a transistor :). The type of transistor will depend on your current consumption.
Transistors typically have three pins, collector (input), base (signal from Arduino), and emitter (output).
You connect the positive external power for the LED strip to the collector, and the strip itself followed by ground to the emitter. Then, you can PWM the base of the Transistor with the Arduino to control how much 12V electricity can get through.
I'm sure there's a transistor tutorial someone can supply.
When choosing a transistor to operate with an arduino, are there any specifications I should pay particular attention to (aside from the current rating)?.
Also look for high voltage ratings, and there's something called "Base-Emitter" or "Base-Collector", and I believe that should be something near 5V, but that could be wrong :P.
When choosing a transistor to operate with an arduino, are there any specifications
Yes, the gain (Ihf).
The gain is the factor by which the base current is multiplied.
If the gain is too low, you won't be able to switch the transistor on with the 40mA that is the maximum current for an AVR pin.
Yes, the gain (Ihf).
The gain is the factor by which the base current is multiplied.
If the gain is too low, you won't be able to switch the transistor on with the 40mA that is the maximum current for an AVR pin.
That's what I was thinking of. Also, you should try to keep under 30mA for continuous use.
i was trying to do the same thing but using RGB strips instead of the single color ones so i needed 3channels so i started playing around with a easy cheap way do do it and i found that for $25 and a simple mod i could use this RGB amp RGB Amplifier 4A/Ch Mini you just pop off the cover and solder a jumper across the 3x diodes on the left side next to the input and then you can connect the RGB inputs to 3 of the PWM ports on the arduino and the + to the 5v pin and it works great and gives you an easy opto-coupled 4A/Ch controller:-) now all i have to do is figure out how to set it up with a 3ch analog input capable of reading 0-12v (maybe with a voltage divider) processing and outputting the signal to the amp so i can use a RGB remote control or let the software control it like a 3 way switch