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1  Using Arduino / Project Guidance / Re: Micro elevator with stepper on: November 09, 2012, 03:20:42 pm
You could, but I presume the elevator also goes down.  So there should be similar code for moving the stepper in the opposite direction.

On the other hand I was thinking of still using hall sensor(s) (you could use one sensor on the elevator or one per floor, depending the available IO pins) to detect the elevator actually passing by a floor.  However, you'd have a couple of flag variables; e.g. one set to "true" when the motor turns clockwise and the other set to "true" when it moves counter clockwise.  Then you have an conditional blocks similar to below...
if (sensorTrigged == true)
   if (clockwise == true && counterclockwise == false) floorNumber = floorNumber++;  //check both flags to rule out some potential errors
   if (clockwise == false && counterclockwise == true) floorNumber = floorNumber--;
2  Using Arduino / Project Guidance / Re: Micro elevator with stepper on: November 09, 2012, 01:42:46 pm
Have a counter that increments or decrements based on both the hall sensor(s) and which direction the motor is running at the time the hall sensor(s) trigger.
3  Topics / Education and Teaching / Re: A DFRobot Fritzing parts library! on: November 09, 2012, 09:36:45 am
Really not a fan of Fritzing. I would go with EAGLE any day of the week over Fritzing with circuit designs.

Eagle is a better PCB design tool, not surprising because it focuses on just that, and so it's my primary PCB design tool.  I use Fritzing more to plan-out and document the wiring between modules, PCBs, and other sizable components.
4  Using Arduino / Motors, Mechanics, and Power / Re: Turning a rotary dial on an old phone on: November 07, 2012, 02:47:56 pm
As far as the output of the stepper motor, I don't think a lot of torque will be necessary to move the dial for a couple of reasons.  First, these dials were intended to be turned with a finger and usually one that could be attached to a pre-teen child or elderly person, not just an adult in their prime.  Second, you are planning to use some sort of mechanical drive using cogs/gears and with the proper gear ratio it can provide increased torque in exchange for slower rotation, which shouldn't be a problem since a human operated dial wouldn't be fast to begin with.  Therefore the stepper motor you have is likely to be up to the task.

As far as interfacing controlling the stepper motor... With a well made shield with libraries and online tutorials available, like the one from Adafruit you are planning on using, it shouldn't be any more difficult than controlling a servo.  Although the wiring and commands necessary for the two devices are will be different.  
5  Using Arduino / General Electronics / Re: Beginner-How many and what voltage power supplies i will need for my project ? on: November 07, 2012, 02:19:42 pm
You should also take a look at this tutorial on de-coupling, adding capacitors or low-pass filters to reduce noise in the power loop.  It is a good introduction to the topic and was written by a very experienced and knowledgeable member of this forum, Grumpy_Mike.  His site also has some useful information on various other topics as well.
6  Using Arduino / Project Guidance / Re: Simple emoticon display. on: November 06, 2012, 06:17:13 pm
Looks like adafruit has them in stock:  $19.95
The other information was great johnwasser, but a LoL shield could be a bit bulky for the look this costume is trying to achieve.  A smaller and slightly cheaper alternatives would be Adafruit's 8x8 LED matrix, $11.95.  It's also Arduino compatible.  Here's a link to Adafruit's tutorial for that one.
7  Using Arduino / Project Guidance / Re: Using Arduino to output (via USB) to a nerf gun? on: November 06, 2012, 03:50:37 pm
While you are getting those links that PaulS mentioned... smiley-wink 

Theoretically it would be possible, but you'd have to know the command signals sent over the USB's data line.  If they aren't in the documentation, you'd need an oscilloscope or logic probe and a little work to determine the necessary commands.  Basically you'd take USB (use a 2.0/1.1 cable, I'm sure this type of desktop toy doesn't need a 3.0 USB bus) with at least one USB plug A and cut that plug off along with some spare cable.  Attach the data lines (see here) to either the 'scope or probe so you can read the signals being sent.  Then plug the modified cable into your computer, start up the program used to control the nerf gun, and finally record the data pulses associated with each specific command sent by the program.
8  Using Arduino / Project Guidance / Re: Simple emoticon display. on: November 06, 2012, 02:07:16 pm
Oh, this is not for Halloween, it is for Dragon*Con in August of next year.

Oh good, you still have plenty of time to work on this.  It's just that since the original post was in October and the thread mentioned costumes, but didn't mention a different time frame... smiley
9  Using Arduino / Project Guidance / Re: motorcycle helmet HUD and auto texting on: November 06, 2012, 11:33:48 am
As rogue_wraith and PeterH have stated, this is potentially dangerous project, especially using any type of commonly available LCD for your HUD.  The only types of display that I can think of that wouldn't have most of the drawbacks they already mentioned would be using some sort of holographic projection or thin film display with completely transparent "whitespace" and could be securely glued to the visor.  However, I don't know if commercially available versions of either technology exist, especially in a form useful and affordable for this type of project.  Even if they did it might not solve all the optical complications, and there still is the potential for obstruction and distraction.

I don't know if you should abandon this project, but if you proceed you'll should do a lot of research into non-standard electronic displays and do a lot of prototyping and safety testing (even potentially destructive physical testing) before you even think using this while on a motorcycle on private property, much less a public road.
10  Using Arduino / Project Guidance / Re: air quality art installation with air compressors PLEASE help!! on: November 06, 2012, 11:07:48 am
Another consideration is how do you plan to get the air quality data the movement is based upon.  If the data is from local sensors (i.e. sensors in or around the "breathing" wall display) you can wire them directly to the control unit.  However, if the data is coming from sensors blocks away or aggregated from all over the city you'll probably need some sort of Internet connection (wired or wireless) or RF transceivers.  In either case you could use an Arduino-based system, but there can be a significant difference between the two in some of the parts you need, how you put them together, and the programming.
11  Using Arduino / Project Guidance / Re: Simple emoticon display. on: November 06, 2012, 10:40:04 am
Is there a particular online site that is best to buy from?
I wouldn't say there is only one.  However, I've had good experiences with products from both Adafruit and Sparkfun, and they both have starter kits (check the links).  There's also the official and still fairly new Arduino Starter Kit, though you'd probably want to buy it from a North American distributor (e.g. Adafruit sells them).

By the way, did you get what you wanted accomplished on the costume in time for Halloween?
12  Using Arduino / General Electronics / Re: About the article "10 Ways to Destroy an Arduino" on: November 06, 2012, 10:26:06 am
There will always be a bit of margin they add and a tolerance from device to device so pushing beyond what the data sheet says is possible, but it dosn't make it any the less a very stupid moronic thing to do.

This is one of the most important things to keep in mind while reading datasheets.  While primarily informative documents; they also serve a role as marketing documents, specifically to designers and engineers.  Both purposes have no room for humility, every aspect of the part the manufacturer believes relevant to its use will be included.  About the only reason a component would capable of reliable performance of some type beyond what is written in the datasheet is that the manufacturer didn't bother to test that particular case.  This last point is why the "name brands" of the electronics industry tend to have longer datasheets with more performance charts and greater information about potential applications, they simply can afford to run more validation testing.  However, no matter who made the component they would not intentionally downplay or neglect any potential positive aspect of its performance.     
13  Using Arduino / Project Guidance / Re: Weather Station and Solar tracker on: November 05, 2012, 02:21:51 pm
I'll start reading about SLA batteries - thanks for the tip.

They are also referred to as VRLAs, the most common type you'd find in hardware/department stores would be as replacement batteries for emergency or outdoor security lights.

On the suggestion of a voltage regulator: I agree that's a good idea and I'm not familiar with how they work.  If I have a solar panel that outputs 9V in daylight, that voltage level will obviously fluctuate depending on time of day and clouds, etc.  The 9V should be good for an arduino to run on, but do arduinos handle the voltage fluctuations?  Would it be better to regulate it back to a constant 6V?  Or perhaps run everything off of the battery and only use the solar panel to recharge batteries during the day?

There are two main types of voltage regulator you'd use on small to mid-sized electronics projects, linear regulators and switching regulators.  Both can usually handle a varying input voltage, provided it stays within the operational input voltage range for the specific regulator. 

The official Arduinos, and most of the derivatives, use linear voltage regulators to provide the proper voltage for the micro-controller and pins to power off-board devices (i.e. the ones marked 3V3 and 5V).  These are effective, but inefficient because the decrease in voltage from the input to the output + the voltage dropout (basically the voltage drop necessary for the regulator to function) has a proportional relationship to the heat generated by the linear regulator.  The amount of waste heat generated, therefore how inefficient the regulator's performance is, depends on the excess power it has to dissipate and that's determined by the decrease in voltage at a given current level.  So for your application this heat is going to be wasted energy, which will decrease the effective battery life for your project, and will increase the temperature within whatever encloses the electronics. 

For example, if you had 9 VDC coming into an Arduino's barrel jack while the board is drawing 250 mAs, the power needed to be dissipated would be ~3 VDC (for the sake of argument I'm just using a voltage dropout of ~1 VDC the exact value will vary with the current) * .250 A = 0.75 Watts.  If you had 12 VDC as the input the power to be dissipated would be about twice as much.

In contrast, switching regulators use components like capacitors and conductors to store energy and release it at specific intervals to either raise or lower the effective output voltage.  They are very efficient (over 90% efficiency is very achievable) and generate relatively little heat, but can cause some ripple on the output voltage and other electromagnetic interference issues.  Many pre-built modules have capacitors or filters to reduce or eliminate these unwanted by-products.  Although if you get one without these, or they aren't sufficient, you should add them to your design.  Here's an example of a step-down regulator module on a small PCB, and here's an even more compact one in a potted package.

Finally, one slightly different alternative I didn't mention is to just have a step-up or step-down (whichever is appropriate) transformer.  A transformer can convert between two voltage levels, but it doesn't have a fixed output level.  Instead, the shift is proportional to ratios between the primary and secondary windings.  So you would still need to use a voltage regulator for the Arduino (but the built-in one would be fine).  If the battery would need one to charge would depend on the type, for a LiPo I would want some voltage regulation but a SLA would work provided the voltage highest voltage is a volt or two above the battery's nominal voltage.  Also, a the power on each side of the transformer will be equal (minus some internal losses because we are dealing with real world devices) so for a given voltage increase or decrease on the output side, the current will change inversely as well.   
14  Using Arduino / Project Guidance / Re: Several usb cables supplying power? on: November 05, 2012, 12:55:17 pm
I agree with retrolefty.  Theoretically the USB ports could be made to handle the proposed situation.  However, you really don't have a way to know if that's true, and trying it could mean seriously damaging your laptop.  Furthermore, given the desire to reduce volume, mass, and production costs; I doubt most laptop manufacturers would make the USB ports that robust in a consumer model (a ruggedized model intended specifically for industrial/military/remote field work could be another matter though).

An alternative would be to use a commercially available back-up power pack made to recharge multiple portable devices simultaneously, like this one (I haven't used this specific model, it's just an example).  Or wire plugs for each of the Arduinos' barrel jacks to a separate battery (perhaps a spare laptop battery so you don't have to worry about a separate charger) and, depending on the battery's nominal voltage, some step-up/step-down circuitry. 
15  Using Arduino / Project Guidance / Re: Information for a rover on: November 02, 2012, 03:19:29 pm
I was thinking along the lines of the possibility of Raspberry Pi running the object avoidance and communicating commands with the arduino.

Well in that it could be feasible, but all the actual obstacle avoidance logic (AKA "the hard stuff") would be done on Pi.  So for questions about that you'd probably want to go to their official forums.  An Arduino would still be useful for controlling the motors, but that's relatively simple compared to visual object detection and ranging.
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