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46  Using Arduino / Microcontrollers / Re: Arduinos original PWM on: October 26, 2012, 09:25:15 am
But i have a second question smiley
I am using a Motor Driver (http://www.pololu.com/catalog/product/757) which is controlled by the PWM at Pin6. While i am driving the DC-motor, i can hear a continous sound like *peeeeeeeeeeep*
I thought this could be the hearable PWM, but 500HZ is far under the limit of 3,5KHz...

Even if it was within the audible frequency range, it won't be the PWM signal itself.  The only way you could directly hear the signal would be if you were feeding the PWM into some sort of sound transducer, like a piezo disk or more traditional speaker.

Instead the sound is probably being produced by the DC motor.  Although much quieter than internal combustion engines, electrical motors often aren't completely silent especially when they are moving a non-trivial load.  From your description it's difficult to determine if the sound is normal for the motor and the conditions it's working under.  However, unless it is loud it likely is nothing to worry about.
47  Using Arduino / Project Guidance / Re: Emergency Vehicle Project on: October 26, 2012, 09:08:19 am
Is there a problem with using a Mega?  I'm using 33 digital outputs and 7 analog inputs (a number I expect to increase), and trying to avoid adding complexity by multiplexing, since I don't understand multiplexing anyway.

No problem at all, especially if you already have a Mega available.  However, the Mega ADK would mean creating a dock with both power and a direct USB connection simpler because you wouldn't need to integrate a USB host shield into the design.  It would also be slightly cheaper if you don't already have both a Mega and USB host shield that could be used for this project.  To be clear though the Mega ADK has exactly the same number and type of I/O pins as a Mega or Mega 2560, it just has an additional IC chip and USB port to provide the USB hosting functionality. 
48  Using Arduino / General Electronics / Re: RF reading for arduino on: October 26, 2012, 08:54:09 am
While most of those RF devices can transmit over long distances, keep in mind that the distance is based on line of sight.  Once you go around a corner, it starts degrading.  Go through a wall and it gets worse.  Same thing with your standard household wireless network router.  Stick it in one room, and walk to a different room and your signal will start to suffer.

Which is exactly why you can get a greater effective range from XBee devices versus Blue Tooth.  XBee modules can easily be setup in a network that allows transmission through intermediate transceivers.  So the initial and final modules don't have to be in line-of-sight of each other, provided they are both within line-of-sight of other modules in the same network.  In this case, three or four modules would probably give very strong and uninterrupted communications link; one on the actor, one some where on the stage, and one or two backstage (or wherever else they need to be to get the signal to where it needs to be).
49  Using Arduino / General Electronics / Re: RF reading for arduino on: October 25, 2012, 05:02:19 pm
im looking into the xbee and I see you can get a shield for it. what exactly does that do for you? is it even necessary. I think I've seen them used for breakout, but in this case it goes right on top of it, so I am not sure what it does.

XBees modules are 3.3 VDC devices, so the serial communication signals going into them need to be at that voltage level and the ones originating from them will be at that voltage level.  The XBee shields I'm familiar with include bidirectional 3.3 to 5 VDC level shifting to make sure a 5 VDC microprocessor (like most Arduinos) can successfully communicate with them.  That is of course in addition to functioning as a breakout board.
50  Using Arduino / Project Guidance / Re: Help for a Noob on: October 25, 2012, 04:05:36 pm
Here's one that a little less expensive from Adafruit.  Adafruit also has a couple of starter kits that are even cheaper, but they include fewer parts (no motors, servos, or ICs).
51  Using Arduino / Project Guidance / Re: Digital Protractor on: October 25, 2012, 03:14:50 pm
I don't know about best, but I've used Proto-Pic a few times.

http://proto-pic.co.uk/triple-axis-accelerometer-breakout-mma7361/

Thanks. Will that breakout board work with the arduino nano?

It should, the Nano has a 3.3 VDC power pin and eight analog input pins (you need one analog input per axis for that accelerometer IC).
52  Using Arduino / Project Guidance / Re: rechargable batteries for uninterruptible power supply on: October 25, 2012, 01:57:52 pm
or a timer that reminds you to change the water in you tropical fish.  Arguably at different ends of a risk spectrum.

Not if you are the fish!  smiley-wink

Actually from the point of view of the fish those two situations would still be at different ends of the risk spectrum, it's just the designation of what end is "Low" and "High" would change.  After all, why would the fish care about what goes on in a human hospital... smiley-razz   
53  Topics / Education and Teaching / Re: A DFRobot Fritzing parts library! on: October 25, 2012, 01:45:31 pm
I tried to import this parts library into the latest version of Fritzing (7.10) and it gave me a "could not open sharable" error.
54  Using Arduino / Project Guidance / Re: Emergency Vehicle Project on: October 25, 2012, 11:48:57 am
If you want to use Android with an Arduino and decided to use something like Mega anyway, I would recommend the Arduino Mega ADK.  The main difference between the two is that the ADK has built-in USB host functionality, so no extra USB host shield is necessary to create a dock like you mentioned.

Something like this Android App based on Firmata might help you as well. It's primarily for BlueTooth interface, but USB interface is also available via a USB host shield or an Android ADK and a high enough version of Android.
55  Using Arduino / Motors, Mechanics, and Power / Re: What to use for locking? on: October 25, 2012, 10:22:49 am
I'm thinking some kind of saloon or revolving door. Ideally I need to restrict to single entries to track people in and out: my perfect solution would be an RFID detector doorway that just scans everyone, but it seems that kind of range isn't easily (or inexpensively) achieved.

Instead of locking a door why not rig-up a custom optical turnstile?  

Edit: What I mean is have multiple optical/IR sensors arranged horizontally a half inch or so apart, about midway up your doorway/passage-way, that trigger when something goes past them.  You'd need at least two, but three or four could make it less error prone.  You wouldn't even need a barrier because the sequence of the sensors being triggered indicates if someone is entering or exiting.  For example if you three sensors labeled 1, 2, 3; triggering the sensors in increasing order would happen for movement in one direction, sensors triggering in decreasing order would mean movement in the other.
56  Using Arduino / Project Guidance / Re: Can I make an Arduino control an arduino rc car? on: October 25, 2012, 09:36:01 am
Great Point Peter. The good part is that I'll be close to it controlling it. Distance wise it wont go out of sight...We hope!

If possible, I would have a floating RF antenna connected via cable to the ROV.  Other than a cable directly to the control unit, that would be the simplest way to communicate the the ROV.  There have been a few previous threads dealing with underwater communications and submersible ROVs (like this one ).  The fact of the matter is that wireless communication underwater is significantly harder to do reliably than in air.  Not only are most of the RF bands greatly attenuated, but most optical frequencies as well.  Even ultrasound, which at first glance would be more effective underwater has potential problems, including varying propagation speed potentially causing a signal to interfere with itself and with thermoclines (sharp boundaries between two layers of water with significantly different temperatures. 
57  Using Arduino / Motors, Mechanics, and Power / Re: Questions for speedometer moto with arduino on: October 25, 2012, 09:09:54 am
You're welcome, good luck with your project.
58  Using Arduino / General Electronics / Re: How potential/voltage dividers compare to voltage regulators? on: October 24, 2012, 04:47:16 pm
From what I read, a potential divider set up does exactly the same, but with 2 resistors instead of a regulator.  It also doesn't need a heatsink, as it doesn't generate any heat to clip off the voltage.  Is that right?

As others have noted, current flowing through any non-superconductor will generate at least a little heat due to innate resistance.  In fact, an easy way to make a small  electric heater is to wire-up low value resistors in series and run a few amperes of current through them.

Also there's the fact that a voltage divider has a fixed proportion the input voltage is reduced by, not a fixed value it reduces the input voltage to.  So if for some reason the 9 VDC is increased significantly, e.g. to 12 VDC, the output voltage will be too high to power an Arduino.  By contrast a linear regulator will give you a known output for any voltage within the range of rated input voltages.

Edit: I forgot to mention that the resistors in the heater example would be 0.5 or 1 W resistors.  smiley-red
59  Using Arduino / Project Guidance / Re: boost converter on: October 24, 2012, 04:25:27 pm
Now I know these are "online" but if you don't want to buy parts, you might have to say what parts you have.

If arduinopi is amenable to ordering modules online, then I'd recommend this one from Pololu.  It's small and the input voltage can be as low as 0.7 VDC.
60  Using Arduino / Project Guidance / Re: boost converter on: October 24, 2012, 04:20:45 pm
Even if you are making the entire circuit yourself, I'm not sure you can avoid having to order some parts online (or through a mail-order catalogue, but I assume that the somehow shipping is a problem not ordering).  This is because the circuit involves storing energy in a capacitor, inductor, or a combination of the two (which is generally the more efficient way).  Depending upon what's available locally, you might be able to get suitable capacitors and/or inductors without having to order them (but then again you might not).  While a boost converter can be made with discretr transistors, using a purpose-built IC allows for faster switching speeds in the circuit (which again increases efficiency).

In any case, here's a link that might help you with your design.
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