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4606  Using Arduino / General Electronics / Re: One resistor instead of multiple in parallel (For parallel LEDs) ? on: October 04, 2011, 08:33:30 am
Here is the website I used to calculate the 1 ohm.
You put in 3V for the forward bias didn't you?  Instead of something >3.2 which is what your datasheet shows.

The calculator got tripped up because the forward biases of your ideal LEDs was exactly the same as your ideal voltage source.  In the real world, nothing is so ideal.
4607  Using Arduino / Project Guidance / Re: interface with floppy and use to play music with MIDI on: October 03, 2011, 09:40:29 pm
it is a floppy drive being interfaced with an arduino + playing "music" from midi sent over serial.

Just a minor point... Mike Kohn isn't using an Arduino.  He is using a ATmega168, but it is stand alone (and doesn't appear to be using an Arduino boot loader.)
4608  Using Arduino / Installation & Troubleshooting / Re: hex file on: October 03, 2011, 02:45:26 pm
Have you any idea why they did that?
It would seem to be much more convenient to have a fixed directory.
Fixed directory might be okay, if you only targeted one host platform.  The Arduino IDE is based on Java and cross platform environments like Java try to respect each of the host operating systems they run on.

Windows (and each of its variants), OSX, and Linux all handle temporary directories slightly different.  The Java environment asks the OS for a temporary directory which the Arduino IDE uses.  The host operating system creates this random directory (in most cases), not the IDE.
4609  Using Arduino / Sensors / Re: AnalogRead on Seeeduino Film? on: October 03, 2011, 02:15:25 pm
What if you tie A1 directly to ground?  Does the A/D read 0?  If you leave it floating do you get random values?

Have you tried using the other analog inputs? 
4610  Using Arduino / General Electronics / Re: One resistor instead of multiple in parallel (For parallel LEDs) ? on: October 03, 2011, 01:48:47 pm
If you want control of individual LEDs, rows, or columns that this matters.  It matters because then the amount of current being drawn changes.  When current through a resistor changes so does the voltage it drops.

1 ohm?
I'd like to see your math. That doesn't sound likely.

If I want to array like that about 100 LEDs.. will a 9V battery be enough to keep the light on for a couple of hours?
9V batteries have about 500mAh of capacity.  So if your leds draw 20mA each, that means you are drawing 2A.  So your battery (assuming it can actually supply 2Amps continuously) will last less than 15 minutes.
4611  Using Arduino / Programming Questions / Re: Question about pin13 (when not using it) on: October 03, 2011, 12:48:50 pm
Is there some way to see if the serial port is open/close? (because of the reset)

Don't power the board from your computer.  Do you have a USB "charger" that plugs into the wall and provides a USB port?  If so, check that its output is 5V and use that to power the Arduino.

Otherwise, you'll have to look through all of the processes running on your computer and determine if any of them might be checking the serial ports.
4612  Using Arduino / Programming Questions / Re: Storing Keyboard input on: October 03, 2011, 12:46:13 pm
The answer will depend on what other kinds of input you want to handle.

You need to determine a way to store numbers as they are entered or process the strings afterward.  If you are thinking along the lines of taking a line of input like your example:  "2.2/2<enter>" and then showing a result of "1.1", there isn't a simple method for that.  Not impossible, but not 1-2 lines of magic code either.

When dealing with numbers, it is helpful to remember that powers of 10 move an integer to different orders. 
2 * 1.0 = 2.0
2 * 0.1 = 0.2
2.0 + 0.2 = 2.2

You'll need to flush out your idea and give more details on what you are trying to accept as input to get more detailed help.
4613  Using Arduino / Programming Questions / Re: Question about pin13 (when not using it) on: October 03, 2011, 11:29:22 am
Resets also occur anytime the Arduino's serial port is opened or closed.

There could be software on your PC that is "scanning" for Serial Ports.  This behavior will cause the Arduino to reset.  Often, software associated with cellular-broadband adapters do this type of scanning.
4614  Using Arduino / Programming Questions / Re: Why are there so many global variables in the examples? on: October 03, 2011, 11:24:48 am
This is probably the start of a flame war (which I doubt was your intent.)

The Arduino platform appeals to a large audience.  Some people just want to make some kind of flashy blinky project, some people want to build robots, and others are do things nobody ever thought possible.

The examples tend to be simplified to make them more readable than to teach programming concepts.  Not everyone who uses an Arduino is (or wants to be) a programmer...
4615  Using Arduino / Programming Questions / Re: trouble using millis() for timing less than 0.5sec on: October 03, 2011, 11:16:49 am
1.  Please use the code tags when posting code (or press the '#' in the editor.)
2.  Integer contants will result in integer math.

Is not the same as:
4616  Using Arduino / Project Guidance / Re: Powering an Arduino on: October 03, 2011, 10:58:52 am
But why do others say that using a 9V will fry my Arduino?

Nobody said that.  We were making the point that 9Vs are very lousy choices for most projects because of their low current capacity.  After using one your next question was sure to be "why doesn't this work for very long?"
4617  Using Arduino / Programming Questions / Re: PORTA,PORTB, PORTC on: October 03, 2011, 10:41:10 am
How can you sample all of the pins, using PORTF ect, does the register some how return the A-D value?

The register ADMUX determines which pin is muxed to the A/D.  The result of the conversion would be in ADCL and ADCH.

PORTF,etc (assuming that is the right PORT) would only be used when the A/D pins are used as digital I/O.
4618  Using Arduino / Project Guidance / Re: Powering an Arduino on: October 03, 2011, 09:25:39 am
I hope you have deep pockets.
The next one-line out of context question will be, "Why does Arduino stop working after a few minutes?"
4619  Using Arduino / Project Guidance / Re: Passionate about trash on: October 02, 2011, 10:07:00 pm
I figure if there was a bunch of intelligent folk anywhere able to do this, it's here
There is no shortage of good ideas in the world.  There is, however, a shortage of people to execute those ideas.
4620  Using Arduino / Installation & Troubleshooting / Re: Shorted out Uno while successfully running soleniod actuation sketch on: October 02, 2011, 09:53:42 pm
Initially, the chip on the arduino is very hot to the touch.
Which chip?  The ATmega?

If your ATmega is removable, remove it.  If the PC recognizes a Uno is attached, then the board and 8u2 (serial to usb) is working.

If anything on the board is hot (or even warm) to the touch, when connected to usb and no other hardware is connected, then that chip is likely dead.
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