I'm about to start a multi-LED project. All my parts arrive in a few days, so at this point I'm thinking it through and would love any advice from the experts on this board... gotchas I should be aware of, etc. [I'm have medium-level experience with this stuff but haven't built anything as large as this before.]
The project: drive 48 white PWM'd LEDs via 3 TLC5940's and a battery-powered Arduino.
The LEDs I'm using are LilyPad bright white (http://www.sparkfun.com/commerce/product_info.php?products_id=8735) with inline 100ohm resistors. I'll probably use a LilyPad board although I also have a few other varieties at hand, like the ArduinoUSB and SparkFun Wee. Software's not really an issue; I've already written a test case that animates correctly with 4 LEDs using the native PWM outputs. The various online resources I've found have been incredibly helpful so I'm pretty sure I'm ready to switch to a 5940 library and do serial output instead of directly driving the LEDs on Arduino pins. I've found great docs that show how to set up a single 5940 and I think I can handle the chaining to get 3x16 = 48 separate PWM'd LEDs.
My concerns: * power usage - Can a single Arduino board power 48 LEDs? The data sheet shows them using ~20mA so that's close to an amp if all on, but my application doesn't really need more than a few to be simultaneously lit. If I do turn too many on, can I hurt the Arduino? (I've read that the 5940 has current limiting built in so it seems safe.) * power supply - I'm planning on using a few rechargeable AA's but don't know the best configuration. LilyPad requires 3.3V but the power supply (http://www.sparkfun.com/commerce/product_info.php?products_id=8466) is out of stock now and I don't know of an existing batter-powered 3.3V supply I could sub in. I'm not very familiar with regulator circuits but I suppose I can copy the LilyPad's schematics and build my own to use a few AA's in parallel? And the ArduinoUSB I have can run off of a 9V so I have that as a backup plan - the LilyPad just has a more convenient portable form factor. * pre-wired resistors on my LEDs - they're 100ohm. Is that a problem? I've typically been using 1Ks but that's on the ArduinoUSB with red LEDs. My calculations tell me 100 is perfect for a 3.3V (white) LED from a 5V source, but I don't know enough to reconcile in my head how this can still work on a 3.3V supply (both LilyPad and 5940 are 3V)
Well, those are the only concerns I can think of right now. I'm sure I'll hit some snags along the way, but the excellent tutorials produced by forum members are giving me confidence that this shouldn't be too hard...