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631  Using Arduino / General Electronics / Re: Can I use this solar powered battery charger to recharge my AA batteries? on: July 13, 2012, 01:50:48 pm
If the device powered by the said batteries draws only 30mA, for example, in a few days, the batteries will become fully charged, but the solar panel will still provide 100mA. Aren't they going to become overcharged and heat up?

It really depends on the type of battery.  In my reply I was assuming NiMH since that type was mentioned earlier in the thread.  You can use trickle charging to maintain a full charge on NiMHs, the usual recommendations are a trickle current between one thirtieth (1/30) to one fortieth (1/40) of a battery's C rating.  Since 2500 mA/30 = 83.333... mA, if you put the load circuit and the battery in parallel you might be able to do it safely (over stressing NiMHs will produce hydrogen gas which is of course flamable and explosive if it builds up in a small space).  Although you might want to consider adding in a current limiting resistor in series with the battery (probably after the diode used to keep the solar cell from discharging it at night) or use a dummy load (i.e. one or more resistors) in parallel with your actual load and battery to siphon-off even more of the current.
632  Using Arduino / Displays / Re: Repurpose Palm LifeDrive TFT on: July 13, 2012, 10:45:23 am
I'm sorry I can't directly help you with your subject question.  However, I do have some advice for your project in general, especially since you're new to DIY electronics.  While I'm all for repurposing components like the LifeDrive screen, the display used will likely be one of the easier parts of this project to modify in code down the road.  Furthermore, during the early stages a standard-sized character of graphical LCD should be sufficent to do your initial development.

Therefore, I hope the information search on how to use that paricular screen isn't stopping you from doing the other, more essential parts like deciding on how to store these preferences, defining the I/O requirements, creating and testing the basic thermostat control algorthim, etc...  Once you get the fundamental parts of your project working, then you can focus on making it "pretty" in whatever sense of the word you want. smiley
633  Using Arduino / Motors, Mechanics, and Power / Re: Can a battery explode on: July 13, 2012, 10:27:20 am
All batteries are a chemically-based energy storage device and under the right, or should I say wrong, circumstances all types have the potential to destructivly release their energy, many in ways like combustion or ignition.  However, the likelihood of this happening depends on many factors, the most important are energy density the chemicals used in the battery.  As noted, LiPo batteries have a relatively high chance of type due to their high energy density and the fact they use lithium (which is a highly reactive element), so even realtively small LiPo batteries (i.e. even "button" type cells can experience ignition) can fail in rather spectacular and potentially dangerous ways.  On the other end of the scale are alkaline batteries, which have very little chance of exploding in the way you probably mean it.  However, they can rupture (sometimes significantly ripping through the battery) and/or leak if abused, which while not fun to watch still releases potassium hydroxide.  A substance which can cause chemical burns in sufficient amounts.
634  Using Arduino / General Electronics / Re: Can I use this solar powered battery charger to recharge my AA batteries? on: July 13, 2012, 09:43:24 am
Its a very inefficient way to charge AA batteries.
By "inefficient" you mean that there energy is lost somewhere, or it's just a slow?

In real-world designs energy is always "lost", even running current through copper wire uses a small amout of energy. smiley-wink

But seriously it would be slow, even though a nominally 15 VDC solar panel could charge 9 (possibly 10 in strong sunlight) AA batteries at a time.  If the AA batteries have a 2500 mAh capacity, and the average current from the solar cell is 100 mA; it would take at least 25 hours to fully charge the batteries (in real-life it would probably be somewhat slower).  Given that most places on Earth have less than 12 hours of sunlight during the majority of the year, that's about three days total...  Unless of course you only plan to use this charger within either the Arctic or Antarctic Circle during their respective summers, then it would be just over a day. smiley-wink  
635  Community / Products and Services / Re: which arduino board is better on: July 13, 2012, 09:18:23 am
The UNO R3 can easily have the processor replaced if you damage it. With the SMD you throw the whole thing away and get a new one.

Another nice thing about the R3 having a socketed, and therefore replacable, main IC is that you can use R3 for initial sketch development, testing, and chip programing; then use the program chip on a custom PCB.  This is especially nice for projects where USB, or even FTDI headers, won't be used in the final project.  Therefore adding external communication just to program the chip would be inconvinient and require more space, time, and (albeit minor increase in) cost for something that's only going to be used once.  Similarly you can also create a "library" of pre-programed chips for back-up or to temporarly change the function of the board without having to connect it to a computer and compile a sketch.

That stated, I have and use both R3 and SMD Uno boards.  If you want to dedicate a stock Uno board to a particular device, the R3 has no advantage over the SMD.  It's all about using the proper tool for the job. 
636  Community / Products and Services / Re: Spray on Batteries on: July 12, 2012, 02:41:04 pm
What? No spray can batteries at WalMart? I feel cheated.
Maybe when they start selling gloveboxes (note: not the type that come with an automobile) as well, but probably not before that.
637  Community / Products and Services / Re: Spray on Batteries on: July 10, 2012, 01:40:14 pm
It's an interesting technology to be sure. However I agree with johnwasser, currently these things are not commerically viable.  Still after several years of development they'd probably be very useful in some applications, especially for inexpensive micro sensory and e-textile projects.  

Furthermore while it might hamper initial R&D, I don't think the electrolyte handling and oxygen-free requirements will be a big issue to eventual large-scale production.  Automated equipment will work just as well in a 100% nitrogen atmosphere (probably the easiest non-oxidizing atmosphere achievable on Earth) as it does in normal air and systems dealing with reactive or sensitive chemicals are nothing new either.  Although unless the production requirements change, this technology will probably not be something most hobbiests will be able to play around with at home.

Edit:Fixed typos...
638  Using Arduino / Motors, Mechanics, and Power / Re: Servos Aren't Supposed To Smoke - Are They? on: July 09, 2012, 01:57:20 pm
It's very possibile to replace servo control boards and their are some available to hobbiests.  A good place to start looking would be
639  Development / Suggestions for the Arduino Project / Re: Is Arduino Due coming? on: July 09, 2012, 01:25:52 pm
I wouldn't give up on the Due just yet, as there are a small number of "beta boards" currently in existence.  However, I wouldn't hold my breath either...  The best answer to your question is probably: "Yes, but we just don't know how long it will take."   
640  Topics / Device Hacking / Re: Arduino Bluesmirf and Android on: June 29, 2012, 04:30:42 pm
I know I'm a little late on the scene, but to go along with what cyclegadget posted, do you know about either the Arduino ADK or IOIO?  The Arduino ADK is an modified Arduino Mega designed to interface with Accessory Development Kit (ADK). 

IOIO a purpose-built microcontroller board, somewhat similar to Arduino Uno, but purpose built and program to interface with Android devices (1.5 and higher).  Of the two the IOIO is cheaper (~50 USD) and would probably be much easier to interface with multiple individual Android devices, but it's designed to act as primarily an accessory to the Android device(s) (i.e. you don't program the IOIO directly, instead code is run through an app on your smartphone/etc... and instructions are sent to the IOIO) and not setup to do much without an Android device controling it. 

On the otherhand, the Arduino ADK is a fully functional Arduino Mega that's been changed to interface more easily with Android devices so it can also run as a stand alone microcontroller.  However, you likely still need to program a custom sketch for your project and its more expensive (~80 USD) than either the Arduino Uno or the IOIO.  Although it has more I/O and its processing power and storage space are significantly better than either of those boards.
641  Development / Suggestions for the Arduino Project / Re: the future of arduino on: June 29, 2012, 10:51:28 am
I think that is just a different market. Your water tank monitor, beer manufacturing device, or fishtank feeding system, doesn't need sound, video, ethernet etc.
Do not agree with that. Your water tank monitor, beer manufacturing device, or fishtank feeding system, DOES need ethernet or wifi, for remote control.

And there are shields and other methods that currently allow the atmega328-based Arduino boards to use either ethernet or wifi (and sound, video, etc... for that matter), if that is deemed necessary for a project.  Yes, it would be more convenient for some with a chip that had more of those features built-in. However, the main purpose of a microcontroller is to control and communicate with other electrical and electromechanical devices.  The Uno can do that with enough speed and processing capabilities for a huge number of potential applications (remember that the first generation of true personal computers (circa 1975 to 1984) had less than half the processing speed of an 16MHz Uno, and many only a quarter or less).  IMHO, the Uno and it's derivatives will continue to be viable as long as the atmega328 is available in quantities large enough to be affordable by hobbyists, and that will be several years at least.
642  Using Arduino / Sensors / Re: SHT1X DIGITAL temperature & humidity sensor Arduino 1.0 error on: June 21, 2012, 03:42:52 pm
This problem is also happen to me. How to fix this?
I'm not really understand with MarkT's answer, i have changed "WProgram.h" to "Arduino.h" but it still doesn't work
Please help me because I'm just newbie
Thank you so much

Btw, i get the example program from here:

In what file did you change the "WProgram.h" to "Arduino.h"?  If it was your sketch file and you are using a library that's not enough.  You have to go into the library folder (in this case it should be something like ".../libraries/SHT1X/") and open the ".cpp" and ".h" files (any basic word processor will be able to open them, they are just plain text files) and make sure to change any reference to "WProgram.h" to "Arduino.h" in those files as well.  The good news is you only have to do this once per specific library and that's generally all there is to get most pre-1.0 libraries to work without a problem.
643  Using Arduino / Sensors / Re: Ping))) and Midi on: June 21, 2012, 03:15:32 pm
First off, it might help if you posted your code for converting the sensor data into the MIDI format.  I don't have much experience in MIDI specifically, but I'm sure there are posters who are and if they actually have the code they might spot a bug you missed in the conversion process. 

Also, according to Parallax the maximum sensing distance is ~3m so if you need absolutely need appreciably more than 2.0m for your project it could be worth it to get a different type of distance sensor, since your getting somewhat close to the maximum range specifications already.  However, I have a suspicion the real problem is your software and not the sensors.
644  Using Arduino / Sensors / Re: Carbon Dioxide Wiring Help! on: June 21, 2012, 10:07:16 am
Yes that's the same sensor.

also, I do not have the money to buy the pre-made board as it costs $50. I don't know what to do :[

I have the Parallax CO2 board with MG811 for use at my workplace, we were characterizing it for possible use in a project.  From my own investigations with it, depending on what you want to do with the sensor the board isn't necessary and might not be worth the extra money.  The main purpose of the Parallax board is the an alarm function, the output is an alarm signal goes high if a manually set CO2 threshold is exceeded (the threshold is set using the board's potentiometer and a voltmeter).  In order to achieve this the board also raises the original sensor signal's voltage from a 250mV to 330mV range to one around 1.8V to 2.4V; but this is only available on test pin vias, not through the premounted headers.  In both cases the lower end of the voltage range means higher levels of CO2.  

As stated earlier, if you don't want the alarm feature and would like a different voltage range (e.g. changed so it's range is closer to 3.3V or 5V and inverted so the higher voltage readings correspond to higher CO2 levels) the Parallax board is probably a waste of money.  In any event, if you want to use this sensor with an Arduino you will need to change the signal's voltage level.  Even using 1.1V as a reference it's difficult to get useful readings from the sensor's direct output and lower voltages are innately more prone to EMI issues.

I hope this helps!
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