How does something like this look?
http://www.reconnsworld.com/ir_ultrasonic_basicirdetectemit.html

Haven't tried it, but seems sane enough to me.

After a round of system updates (including sun-java5-jre 1.5.0-16-2ubuntu2), the fonts in the Arduino IDE (0013) have changed.

Before, the font was monospaced and what you'd expect. Now, the font is proportional, the the cursor misbehaves (not where you think it is) as well. The UI for the IDE is much better looking in general, but the fonts issue is obnoxious.

Anyone else seen this or have a solution?

I feel like this is a silly question, but I'm a bit uneasy about it so I figured I'd ask anyways...

I have some intricate LED devices (eg an RGB LED pen, for long-exposure light drawing) with built in resistors chosen for a 5v source.  I'd like to be able to use these with a 3.3v Arduino clone. Assuming I have a 5v source available, is there any problem with sinking the LEDs into a 3.3v device?

Feeling a bit rusty, thanks for any advice.

Sparkfun is working on something that seems like its exactly what you need, it's a simple 100X op-amp breakout:

http://www.sparkfun.com/commerce/news_archive.php (scroll down to the news for April 16th)

Can't turn down an opportunity to help sexy ladies and sexy things come together...

Have you seen this page?:
http://www.arduino.cc/playground/Main/RotaryEncoders

I don't have the experience with the Max/MSP side of things, but rotary encoders are pretty easy to wire up with the Arduino. That page from the Arduino playground explains them pretty well. There is a basic sketch on that page which will output the absolute numerical counter from the encoder to the serial port on the Arduino.

To convert this number to a rate of speed, you'll want to divide the change in counter by the change in time. However, if you're trying to sync up a movie to the speed of the encoder, this probably won't be fast enough for smooth playback. Personally, I'd consider changing the code to just output a single character per "click" -- 24 per revolution total -- and do the speed computations in Max/MSP. (Or, advance one frame per click...)

Also, I'm not sure if you're committed to the Arduino, but something like this could also work well:
http://forums.bit-tech.net/showthread.php?t=86820

It would let you use a standard USB mouse to detect speed, which would be trivial to patch in.

After messing around with the 741, it seems to be a poor choice due to the complexity in getting it to work with a single-supply design.

Is there a better component to choose for this application? The MOSFET sounds interesting, but I don't have a very good grasp on how to implement it either.

Thanks for the suggestions, I think I'm going to try a 741 opamp, but if I ever need to drive larger currents, I'll keep the MOSFET in mind.

Hi, long-time reader, first time poster.

I'm interfacing some old 0-10V analog gauges to my arduino, and would like to be able to use the full gauge scale, not just 0-5V.

What's the best way to get the 0-5V produced from the PWM outputs scaled to 0-10V? It seems like an op-amp would work, but I'm not sure about the implementation details, or if that's the best way.

Any ideas?