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31  Using Arduino / General Electronics / Re: Soldering mistake... on: July 23, 2012, 03:23:12 pm
Desoldering wick is just braided copper with flux in it. It is really cheap and everyone should have some - but if you're stuck somewhere without it, you can approximate it with stranded copper wire.

Fan out the strands a little, let the solder wick into them, and then repeat until the solder is gone. If you have liquid / gel flux, dip the strands in that first to make life easier.
32  Using Arduino / General Electronics / Re: electronics rule broken? on: July 13, 2012, 03:48:42 pm
Just a thought: I have no idea what sonic relays are, but if they're emitting and detecting sound to close a switch (like a ping sensor), maybe they're interfering with each other? That would explain why one works fine, two get a little flaky, and three don't work at all.
33  Using Arduino / General Electronics / Re: Using fuses to limit current (how to select values)? on: July 06, 2012, 11:21:24 am
I'm surprised: the cable I bought was being sold as an "extension cable", and was labelled that way on the box. I'd expect that a cable intended to be cut into two would have twisted the leads so each distinct pin would have the same colour wire going to it.

Interestingly, if I'm wrong, then others are as well:

http://www.alibaba.com/product-gs/516251450/SAE_2_Pin_Extension.html
http://www.amazon.com/Hopkins-47965-2-Pole-Flat-Extension/dp/B0002Q80RW

I'm learning way more in this thread than I though! :-)

As for caravan vs trailer - I understand these kinds of cables are used more for the type of vehicle that tows boats, rather than rooms in which to camp. I'd call that a boat trailer - not sure what others would :-)
34  Using Arduino / Programming Questions / Re: Serial.write a float value on: July 02, 2012, 06:25:01 pm
For a quick and dirty solution, multiply it by 10000 before you send it, cast it to an int, send the characters as ASCII, and then divide by 10000 on the PC side to get back your original float. (Watch for overflows though...)
35  Using Arduino / Programming Questions / Re: First attempts at Arduino OOP on: July 02, 2012, 05:52:19 pm
Is EEPROM.h being included, or is it not being found? I've always found it useful in cases like this to put #error at the top of the header file you're including (temporarily, of course):

(EEPROM.h)
Code:
#error "Yes I just included EEPROM.h"

If you don't get the error, something is wrong with your include path or location of the header file. You could put it right before the line that defines EEPROM if you want to narrow things down.
36  Using Arduino / General Electronics / Re: Using fuses to limit current (how to select values)? on: July 02, 2012, 05:24:36 pm
Thanks very much for the useful information. In my case I think the fuse blew before the diode and/or traces on the SMT circuit board acted in the fuse's place... which is as good a reason as any to have a fuse in circuit!

(And nothing beats dumb luck when you're ignorant. I didn't even realize my cable was fused... now I'm checking that every time.)

As a warning to others: if you cut a trailer wiring extension cable in half, the red wire is hot on one end and ground on the other:



Pay attention when connecting!
37  Using Arduino / General Electronics / Using fuses to limit current (how to select values)? on: July 02, 2012, 04:55:57 pm
Recently, I had occasion to plug a radio in backwards. Luckily, the inline fuse in the power cord saved the radio. This got me thinking, though.

The inline fuse was rated at 4a 250v. Since the fuse was inline with a battery (12v), does this mean it opened at a different amperage than specified, or will all 4a fuses blow when 4a goes through them regardless of voltage? If not, is there an easy way to convert?

I think I've got religion when it comes to fuses now - all my power cables in the future are going to have them. Losing 20 cents worth of fuse is nicer than losing $50 worth of radio.
38  Using Arduino / Programming Questions / Re: help with this code, pretty please !!!! on: May 04, 2012, 06:53:38 pm
It looks as if your library isn't being imported. Is it in the right place? The error message you're getting is what happens when C++ doesn't know about a class:

http://cplusplus.syntaxerrors.info/index.php?title=%E2%80%98Foo%E2%80%99_does_not_name_a_type

39  Using Arduino / Programming Questions / Re: How to read the state of an output pin ? on: April 23, 2012, 04:03:53 pm
I'm not sure you can digitalRead() an output pin. You might have to keep track of the state manually:

Code:
digitalWrite(10, HIGH);
statepin10 = HIGH;


40  Using Arduino / Project Guidance / Re: 8 Character Limit - Taken out of original concept on: April 20, 2012, 05:47:33 pm
I don't know of a limitation - especially since you're not actually doing anything with audiofiles. However:

Code:
char audiofiles[NUMTAGS][14] = {"hello   ",

you're creating an array of 5 strings that are 14 characters long. That should be enough to fit 13 characters + \0.

What makes you think there's a limitation on string length? What behaviour are you seeing?
41  General Category / General Discussion / Re: If a program could program itself?.... (AI) on: April 12, 2012, 06:00:57 pm
I also looked into genetic algorithms / genetic programming back in the late 90's / early 2000s. It's not hard to come up with a language where every statement is syntactically valid (i.e. it does something, which may or not be what you want) and a fitness function (a way to evaluate a program to determine if it's closer or further away from a desired solution than other instances of a program).

LISP is good because a list can also be a program. Create a million lists at random, execute them all with your dataset, pick the best 50% or so, making sure that the fitness function also has a component that selects smaller programs over larger programs. Then cross-breed the programs (exchange parts of successful lists with parts of other successful lists). That's one iteration. Do a few million iterations and eventually you've got a program that does something like what you want.

The problems: it takes a LONG time to evaluate all the programs, and you might have to have some sort of timeout criterion to prevent endless loops. It takes a LONG time to do all the iterations you need to satisfy your fitness function. Once you've satisfied your fitness function enough, you have something that works for your test dataset - that might not handle all the data you throw at it. The more complicated a thing you want, the longer it will take. Not all problems can be solved with GP: you need a problem that lets you know when you're getting closer to a solution.

See it in action here:

http://alphard.ethz.ch/gerber/approx/default.html

(needs Java)

42  Using Arduino / Microcontrollers / Re: Uno voltage minimum on: April 12, 2012, 05:31:39 pm
Looks like you can run the 328 / 328p at anywhere from 1.8 to 5.5v. Not sure about the speeds you can run at various voltages, but if I had to guess I'd say you'd be safe using the internal oscillator. (Edit: looks like someone answered this question: http://arduino.cc/forum/index.php/topic,101084.0/topicseen.html )

http://www.atmel.com/devices/ATMEGA328.aspx

Also, I believe the analog reference voltage can't exceed Vcc.

The Uno itself has a voltage regulator that needs 6-12v in order to output 5v.
43  Using Arduino / Programming Questions / Re: Ardweeny programing on: April 09, 2012, 12:41:27 pm
Depending on your USB to serial adapter, you might not have auto-reset hooked up to the Ardweeny. In that case, you have to reset it manually with the push button at the right time. Here are some instructions:

http://andrewmemory.wordpress.com/2011/01/30/using-an-arduino-serial-usb-board-with-an-ardweeny/
44  Using Arduino / Project Guidance / Re: Long road to a Thermal Cycler - trying to make a relay work on: March 21, 2012, 03:22:51 pm
If you're doing this for the end result (rather than to get experience with electronics), you might want to take a look at this:
http://powerswitchtail.com/PSTIIU.aspx

Basically, what you want but in kit form, which might be easier :-) They also have assembled units, which is nice because you don't have to touch mains voltage.

The relay won't plug into the breadboard as-is. You'll need to plug it into a socket, and take wires from the socket to the breadboard. Alternately, you can just solder wires to the relay and run those to the breadboard. (Don't put 120v on the breadboard, though!)

You can use a double pole double throw relay as a single pole single throw relay - just ignore one "pole" (leave it disconnected). The "double throw" means the relay will switch two things at once independently, not that it cycles back and forth between them. Think of it like a knife switch:
http://ocw.mit.edu/ans7870/SP/SP.764/imagegallery/lab3/images/1.jpg
where the thing that does the switching is not your hand, but a coil.

I don't think it matters if you have the grounds connected or not - assuming you have a separate power supply for the LEDs and the Arduino, the relay effectively isolates one circuit from the other.
45  Using Arduino / Project Guidance / Re: Newbie with a Radio Scanner idea on: March 20, 2012, 04:11:19 pm
You might want to consider replacing volume and squelch potentiometers with equivalent value digital potentiometers rather than coming up with a mechanical linkage. Reading the screen should be possible, but you'll have to reverse engineer what causes things to appear - there are a number of possibilities. If you know what the values are (for instance because your kepad just typed them), you can send those to the PC without having to read them.

This is probably not the first project you want to tackle. On the other hand, getting a keyboard matrix working and a couple of digital potentiometers changing values might not be too hard to start out with. Good luck!
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