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46  Community / Bar Sport / Re: why do magnets make bigger sparks? on: February 16, 2012, 01:06:54 pm
Do the sparks change if you turn the magnet around? If they do, sounds electromagnetic. If not, maybe the composition of the magnet instead?
47  Community / Exhibition / Gallery / Re: my arduino project on: February 09, 2012, 05:01:39 pm
Nifty stuff! It looks like you've spent a lot of time working on this, and it shows (in a good way!)
48  Using Arduino / Programming Questions / Re: Can you use something like #ifdef to check if a header file is included? on: January 24, 2012, 06:21:34 pm
Yes, if the header file defines something unique. (Most do so in their guard code.)

In other words, most headers will have the form:


So you would put the following in your code:

// Must be using SomeUniqueThing library

If they don't have that, you can look through the header for a #define that is "pretty unique" to that header and test for that. Failing that, I don't know any other easy way. Be wary of different versions of the same libraries, too.
49  Using Arduino / Project Guidance / Re: La Crosse wireless sensors on: January 06, 2012, 06:24:06 pm
The book "Practical Arduino" had a chapter on LaCrosse weather stations... try here:
50  Using Arduino / Programming Questions / Re: newbie altering existing sketch on: December 20, 2011, 07:10:14 pm
This looks suspicious:

  // attach interrupt to reed pin
  attachInterrupt(1, rotation, FALLING);

That says to make use of the interrupt on pin 3. If you don't have pin 3 wired up to the reed switch, you won't be getting the interrupt.

Here's some more detail:
51  Using Arduino / Programming Questions / Re: Reason for missing new() / delete()? on: October 03, 2011, 05:45:19 pm
The sense I get is that if you're writing a library, you should use malloc/free (and in fact, you may have to, since new/delete are gone). If you're writing a sketch for a particular purpose (i.e., the majority of Arduino developers), you should use singleton variables or fixed-size arrays, and not malloc/free/new/delete.

I'm not saying I agree with the decision to remove new/delete - but I can see that at least it makes you pause before going forward.
52  Using Arduino / Installation & Troubleshooting / Re: UNO not saving sketch after power cycle on: October 03, 2011, 05:03:35 pm
Maybe this will help?

53  Using Arduino / Programming Questions / Re: Dallas Temperature Sensor on: September 30, 2011, 06:08:58 pm
In C/C++, you can initialize arrays with a list only when you define the array. So

int insideThermometer[] = { 0x28, 0x1D, 0x39, 0x31, 0x2, 0x0, 0x0, 0xF0 };

is valid, but:

int insideThermometer[8];
insideThermometer = { 0x28, 0x1D, 0x39, 0x31, 0x2, 0x0, 0x0, 0xF0 };

is not.

Initialization from a list is something the compiler does. The compiler actually does the initialization in the first case by reserving the memory and filling in the values at the same time. The compiler can't do anything in the second case - the memory for the array has already been allocated, so a change would have to happen at runtime.
54  Community / Website and Forum / Re: More Sticky? on: September 30, 2011, 05:17:40 pm
While we're nominating good stickies, I'd suggest:,53290.msg380874.html#msg380874

(how put the V1 Uno into DFU mode the "easy way".)
55  Using Arduino / Microcontrollers / Re: Updating the Atmega8U2 -> Invalid HEX file syntax on: September 26, 2011, 03:16:51 pm
I did this a while back. These instructions might help:
56  Using Arduino / General Electronics / Re: Moving from breadboard to perfboard on: September 26, 2011, 03:14:02 pm
Thanks for the advice. I think I'll need to start thinking of Vcc and Gnd as "just one more thing to connect" rather than special lines.

Veroboard looks like a good idea, but I've never seen it available for a reasonable price. If I do I'll give it a try :-)
57  Using Arduino / General Electronics / Moving from breadboard to perfboard on: September 23, 2011, 04:51:53 pm
I've built a few circuits now, and am gradually getting more experience. One area where I run into difficulty is when I move things from a breadboard to perfboard. In particular, what is a good way to transfer +5v and Gnd?

I know there are some perfboards with traces on them equivalent to what you'd find in a breadboard...but they cost more than plain perfboard, and many of them just connect 5 holes together rather than providing busses on the side. For my projects, I've ended up running a +5v rail of bare wire down one side, and a ground rail of bare wire down the other, then soldering wires / component leads to that. It works, but isn't really robust or satisfying.

What do you do when you move from breadboard to perfboard?
58  General Category / General Discussion / Re: Getting Started With Micro controllers on: September 21, 2011, 06:57:49 pm
Start with the tutorials:

The Arduino book is a good resource too ("Getting Started with Arduino").

Here's some doc to explain C programming if you're used to Java:

For hardware, you'll probably want to start with LEDs, resistors and pushbuttons. Motors take a little more interfacing because they draw more current than the Arduino can put out.
59  Using Arduino / Project Guidance / Re: Can I build a connect 4 clone on: September 21, 2011, 05:44:29 pm
I'd recommend you do some research here:;board=6.0

A fair number of people want to control lots of LEDs :-)
60  Using Arduino / Project Guidance / Re: Simple question about the demo projects with the Uno on: September 20, 2011, 05:43:55 pm
The circuit picture appears to be from Fritzing (

Measuring continuity (or resistance) when there's power in a circuit is not going to be accurate. The voltage in the circuit can interfere with the voltage the meter sends down the line to check continuity. It's also a good way to fry your meter. Hope this hasn't happened to you!

If you get continuity between +5 and Ground with no power applied... I can't explain that one.
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