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16  Using Arduino / General Electronics / Re: Solder does not stick to iron after cleaning on: August 06, 2013, 02:01:05 pm
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A little off-topic here, but I was wondering why it seems that everyone spends so much time cleaning their soldering irons, when all it does is make them stop working as well?
Got some evidence for that last bit?

Crud on the tip cuts down on the amount of heat transferred to the solder joint, and can also deposit said crud onto/into the solder joint.  Either produces a poorer quality joint.

A clean tip works better.  I didn't notice this as much with my $12 radio shack iron, but with a good iron you can.

-j
17  Using Arduino / General Electronics / Re: Solder does not stick to iron after cleaning on: August 06, 2013, 01:56:30 pm
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Just for the road it's not a Rheostat dimmer they are big and wast power as heat and are not stable for this.

Im using a Thyristor dimmer

Doesn't matter which type dimmer you're using; a rheostat is simply limiting the amount of power going into the iron without regard to tip temperature.  It is a poor replacement for control with feedback that you get with a good quality iron.

-j
18  Using Arduino / General Electronics / Re: Solder does not stick to iron after cleaning on: August 05, 2013, 01:43:18 pm
If the tip isn't designed for lead-free, the tip will be trash quickly.  I've seen it here at work.

Sticking a rheostat (light dimmer) inline just reduces the maximum output power.  While better than nothing, it's still not as good as proper temperature control with a temp sensor in the tip (I've done it both ways).

-j
19  Development / Other Hardware Development / Re: EAGLE- how to create another package based on existing one? on: August 05, 2013, 09:31:03 am
Open the library where you want to create the new package.  Issue the command

copy old.pac@old-library-name

If you want to give it a new name, append it:

copy old.pac@old-library-name new.pac

You must include the library name even if it's the same library you have open for edit.  (note, this is for eagle 5).

-j
20  Using Arduino / General Electronics / Re: Solder does not stick to iron after cleaning on: August 05, 2013, 06:13:14 am
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I wanted to avoid using this stuff solely based on the harmful health effects of inadvertently inhaling it.

You're not geting hot enough to vaporize lead.  Anything you breathe will be flux, and lead-free flux is on average nastier than tin-lead flux.

Lead free requires a lead-free tip and iron (for the fluxes and the hotter temperatures).

Most flux does eventually go bad.

Use lead solder, keep it out of your mouth, and wash your hand when you're done.

-j
21  Community / Website and Forum / Re: Recommend a mail list? on: July 08, 2013, 08:56:34 am
Hello, fellow dinosaur.

There probably is no useful email list.  the cool kids are using forums.

-j
22  Development / Other Software Development / Re: millis() on linux system on: July 08, 2013, 06:36:44 am
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I found system() call pretty useful.

Yeah, but it's dangerous from a security standpoint and it involves a lot of overhead (fork()/exec() )

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When don't know how to delete a file, just system("rm file"); until I figure it out in C library

I think that one's unlink().

-j
23  Community / Bar Sport / Re: Why aren't more communications (cell phone, email) heavily encrypted? on: June 28, 2013, 09:44:20 am
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What am I missing?

People are stupid/lazy/cheap.  Unfortunately the current state of the art means that using encryption requires the user to be knowledgeable, to think, and to act.

Also remember encryption is only part of the story. Even the metadata tells someone a tremendous amount about you - encrypting your phone conversation so that the NSA can't hear you ask mom "how many kilos of C4 was I supposed to pick up?" doesn't help your security all that much if they can use the metadata to know that you placed the call from Achmed's Bomb Shop.

-j
24  Development / Other Software Development / Re: millis() on linux system on: June 28, 2013, 08:02:57 am
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So "resolution depends on system" means if I set say 0us and then 250us and the system may not even do anything if it is not able to set its clock with accuracy of 250us, right?

That's my understanding.  I've never used this to set time, only to instrument code, and every system has reported at least millisecond resolution.

To set time, I've always used the command line (date, rdate, or ntpdate) or an ntp client daemon.

-j
25  Development / Other Software Development / Re: millis() on linux system on: June 22, 2013, 06:42:56 am
Try gettimeofday() :

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Standard C Library Functions                     gettimeofday(3C)

NAME
     gettimeofday, settimeofday - get or set the date and time

SYNOPSIS
     #include <sys/time.h>

     int gettimeofday(struct timeval *tp, void *);

     int settimeofday(struct timeval *tp, void *);

DESCRIPTION
     The gettimeofday()  function  gets  and  the  settimeofday()
     function  sets  the system's notion of the current time. The
     current  time  is   expressed   in   elapsed   seconds   and
     microseconds since 00:00 Universal Coordinated Time, January
     1, 1970. The resolution of  the  system  clock  is  hardware
     dependent;  the time may be updated continuously or in clock
     ticks.

Here are some macros that I copied from a benchmar program:

Code:
/* copied from mpbench */
#define TIMER_CLEAR     (tv1.tv_sec = tv1.tv_usec = tv2.tv_sec = tv2.tv_usec = 0)
#define TIMER_START     gettimeofday(&tv1, (struct timezone*)0)
#define TIMER_ELAPSED   ((tv2.tv_usec-tv1.tv_usec)+((tv2.tv_sec-tv1.tv_sec)*1000000))
#define TIMER_STOP      gettimeofday(&tv2, (struct timezone*)0)
struct timeval tv1,tv2;

....
main()
...
  TIMER_CLEAR;
  TIMER_START;

/* code to instrument goes here */
...

          TIMER_STOP;
          printf("# threads, calls, seconds, calls/s\n");
          printf("%d,%d,%f,%f\n", omp_get_num_threads(), counter, TIMER_ELAPSED/1000000.0, counter / (TIMER_ELAPSED/1000000.0));


I've used this on Solaris and various flavors of linux (although not Debian).

-j
26  Community / Bar Sport / Re: Be DIFFERENT! make good posts! on: April 27, 2013, 08:45:35 am
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There is something missing on this forum (or at least I can't find it) that can be used on some other forums: the function 'ignore posts from this user'

Oh, for the days of usenet news; the crudest newsreader I ever used was more sophisticated than the best forum software.

*plonk*
27  Using Arduino / Project Guidance / Re: XBee Antenna on: March 18, 2013, 08:46:02 am
A note/caveat to Jack's advice:  you can add coax, but not too much.

If you're using the 2.4GHz xbee (which is most of them), coax attenuates the signal quite badly.  I wouldn't use more than a few inches of coax, 10 or 12 max at 24.GHz.

The U.FL connector xbees can also use an antenna with coax (I think all the U.FL antennas have a feedline, but I could be wrong).

Don't forget that the xbee is a serial device, so it may be feasible to move the whole xbee to a different location.

More information would be helpful.  Like Jack says, what problem are we trying to solve?

-j
28  Community / Bar Sport / Re: Why people don't read error messages, and Clang on: March 16, 2013, 10:38:00 am
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I find it interesting that new programmers often don't read/understand error messages.

No kidding.  I worked helpdesk in the computer center while an undergrad, and you wouldn't believe how many times I had these conversations:

#1:
User: My program keeps giving me a divide by zero error.  What does that mean?
me: you're dividing by zero.
User: Oh.

#2:

User: My program keeps giving me a divide by zero error.  Why?
me: you're dividing by zero.
User: no I'm not, I'm dividing by N.
me: Well, the value of N is zero.
User: Oh.
29  Using Arduino / Project Guidance / Re: XBee Antenna on: March 16, 2013, 10:29:32 am
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it appears to just be a single wire no complete circuit

You're half right.  It probably is a single piece of wire, but it has some specific characteristics - most importantly, its length is equal to 1/4 of the wavelength of the signal being radiated (as measured in the conductor, which is slightly different than the free space wavelength).  This geometry allows the signal to radiate.

If it was an inefficient design (incorrect length, etc), at least some of that power would be reflected back into the power amplifier (special transistor) output, which could damage the amplifier.  At best, the signal isn't getting out of the radio as intended.

-j
30  Using Arduino / Project Guidance / Re: XBee Antenna on: March 15, 2013, 06:07:26 am
It's an antenna, not a random piece of wire.  The length of the antenna element is a function of the frequency.

Depending on the power of your transmitter and how bad the mismatch is, it can cause behavior anywhere from "it doesn't work" to "you just let the magic smoke out of the power amplifier".

There are xbees with coax connectors so you can use an antenna with a short feedline.

Another solution is to move the whole xbee, but there are limits to how far you can run the TTL level serial connection between the xbee and whatever it's plugged in to.  Those limits depend on noise, and a robot can be a noisy environment.

-j
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