Power via USB (simple ambient orb)

Forum 2005-2010 (read only) Hardware Interfacing
1

Hey guys,

I am a complete electronics newbie here so go easy!

After seeing the todbot blog entry about a DIY ambient orb, I went and grabbed myself a Diecimila

Now, I haven't had a chance to play or get my LEDs yet, and just before I do, I wanted to check a few things

What is the maximum power output you can get from the digital or analog outs using just USB power (no external PSU)? I want nice bright LEDs (as bright as possible for a good visible ambient orb), but the maximum output the hardware specs suggest is 40mA per pin which seems a bit low? Any suggestions on what LEDs would be best to use here without causing problems?

Would I be better (get a brighter output) using a composite RGB LED or should I stick to seperate LEDs?

Would the blinkm be a good idea or overkill? Anyone have any experience with this and how bright it is? Would this be powerable via USB alone? It does seem easier to write code for since it's simply a case of passing the "fade" command along with the new hex color via i2c. It certainly seems like a good idea

The main reason I want it to be powered by USB alone is because I want to keep a simple one-wire design for both signal and power

Thanks guys!

2

Standard LED's use about 20mA each. So you could theoretically drive 2 standard LED's from an Arduino pin.

The BlinkM's ae obviuoslly the easy alternative. I don't know their currentconsumption though, but i think people are drivibg them directly from Arduino.

Just remember that you can get 500 mA from the USB port max. And you are not guaranteed that you will get it. And those 500mA are the total for everything connected to the port and Arduino Some of it is used by the Arduino board itself, so you cant use all 500mA to power LED's.

3

I2C requires 4 wires power, gnd, in, out what you're thinking of is One-wire ehich uses 2 wires GND and signal, but for a simple thing such as an RGB led you could just use analogWrite on 3 PWM pins to control the colors

4

I2C requires 4 wires power, gnd, in, out

Sorry to be picky but I2C does not use in and out. But Clock and Data. The Data line is bi-directional.

5

Sorry to be picky but I2C does not use in and out. But Clock and Data. The Data line is bi-directional.

;D Thanks for catching that.

the analogWrite method would take the least amount of memory 0kb extra (already included in default upload), though, the Wiring library is 200 kb extra if i remember correctly.
and RGB leds are pretty bright.
(ascii art diagram for connecting the led )

              GND
                 |
             -------
             /\  /\  /\
            --- --- ---
R            |    |   |
   __/\/\/\__|    |   |___/\/\/\___G 
                  |_______________/\/\/\/\___B

Add appropriate resistors
then you'd go in program

              analogWrite(redPin, redVal);
              analogWrite(greenPin, greenVal);
              analogWrite(bluePin, blueVal);