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4981  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Cheap, small , project boxes on: March 12, 2010, 11:02:39 pm
If you have them in your area, dollar stores typically sell cheap plastic storage containers in a variety of sizes. Craft stores also sell cardboard, wooden, and plastic containers for storage and crafting. There's also discount retailers (like TJMaxx/Ross) that sell decorative boxes that could be repurposed (some would make awesome boxes for steampunk designs).

 smiley
4982  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Buying parts in small batches (I'm a noob) on: March 12, 2010, 11:24:14 am
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Ebay is suprisingly a fantastic place for components. A lot of chinese vendors on there who sell the components at much lower prices than other vendors, and I haven't had any problems. Also good for hard to get items.

Right now it looks like the only place you can go to in order to get small quantities of ATMega168/328 chips; both Digikey and Mouser are out-of-stock, at least until May-July (?) - but there are tons available in China and Asia (check ic2ic.com - compared to Digikey and Mouser - you'll see what I mean).

So, all the drop-shippers in Asia are selling low quantities of these parts - the only problem is that they don't seem to (?) be combining shipping! So, you may be able to get 5 pieces of a 168 for $2.50 each (cheap), but shipping is $5.00 per piece (!!!), which is really, really STUPID.

Of course, I haven't checked with the seller's to see if they will combine shipping, but nothing on any of the item pages indicates that they will do so (small rant: I hate what Ebay has become - I miss bidding on old electronics and such - does anyone have any suggestions on good auction sites run like Ebay used to be, where I can dicker and bid on old electronics items and other garage sale junk? PM me if you do).

But that's just those parts, mainly - and if you are only looking for one or two, maybe the uncombined shipping isn't that bad (still seems like a ripoff, though - I mean, you could probably order 1000 from some supplier off ic2ic if you wanted to, and you wouldn't likely pay even a dollar per to ship them).

I don't know why there is a preference (or market forces?) keeping those chips in Asia (are they doing nothing but churning out Arduinos and other ATMega-based stuff?) - but you can't get them otherwise. It kinda concerns me (I had a small rant here, but I am leaving it off).

Ugh.
4983  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: 4-Button Sequencial Code using Arduino ? on: March 12, 2010, 11:20:30 pm
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BOTH the programming part and the "which one" to choose.

Programming:

If you haven't ever done it, then look at the examples in the IDE, peruse the online reference, check out code in these forums, and check out the playground; try the examples, try changing them to do different things or make them work differently; try combining the code you think you need. Look online for circuit examples, etc and then try to adapt them. If you have a concern, draw up a schematic as best as you can, write up your code, and post it in the appropriate area on these forums for help.

Ultimately, what most of us don't want is to do your work for you; if you show us you are trying, though, we will help you get the rest of the way and hopefully expand your understanding of the Arduino, programming, and electronics.

As far as "which one" for the project:

You will likely be best served by prototyping your project using a regular ole' Arduino Duemilanove (that's Italian for 2009, I believe); later (after you have things debugged) you might want to get a smaller version, or build an RBBB (Really Bare Bones Board), or roll-your-own (standalone). Don't worry about getting a "Mega" or one of the other "big boards"; they aren't needed for your learning, and the extra features might confuse you.

You'll also want to invest in a breadboard and some jumpers; I recommend Elenco for their breadboards (I've had one of the smaller ones for almost 20 years now and it still works great) - they are more expensive than other brands, but worth it IMHO.

Get a set of good jumpers (either straight or flexible - each person has their preference; I prefer straight for on-board runs, with flexible between separated boards or components); for your initial project you'll also want a relay (5V SPDT is fine), some NPN transistors (2N2222 are perfect), a selection of resistors and some cheap standard red LEDs - you might also want to get some pushbuttons, small toggle switches, maybe an 8-position DIP switch, some rectifier diodes (1N4004 is fine), a 7805 voltage regulator (or two), and a 4-cell AA battery holder (for 6 volt output - you can use a 7805 regulator to drop the voltage down properly). You might also want to pick up a cheap servo or two.

Those are the basic parts. Pick up a storage box with compartments to hold the components as well. Eventually, if you really get into this hobby, you will have many rows of those multi-bin storage cabinets; I have several myself, and will probably be shopping for more this weekend (part of my ongoing "clean up my shop" effort)...

 smiley

4984  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Cheapest chip supplier? on: March 12, 2010, 11:26:05 am
I've seen 168s on Ebay for $2.50 US each, approx (drop-shipped from Asia); the problem was the advertisements didn't say the seller combined shipping, and shipping was $5.00 per piece! I have yet to contact any of the sellers.

 smiley
4985  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Few questions about the power of the Arduino on: March 11, 2010, 12:22:28 pm
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Many performance problems are due to poor software design, not the Arduino hardware.

I'd say that more than a few performance problems are caused not just by software design, but system level design included.

Too often an individual or group will come up with an idea, and rush to implement it without fully understanding what the constituent parts do; they don't understand the processes each unit or area manages, nor what those processes entail, or how the inputs and outputs to and from those processes affect the system as a whole.

Instead, they just throw money and hardware down the drain.

The better approach is to design the whole system (to the best of your knowledge and ability), breaking down sub-units of the system into processes, understanding those processes and what resources they require, and how they affect other processes or units, and how others effect them in turn. Those processes may be further broken down into their own sub-processes. Re-iterate, plan, and design as needed.

Once you understand the whole, you can then intelligently, rationally, and logically decide what parts or resources are needed to accomplish the goals of each area; maybe one are needs an entire PC, while another can get by with a microcontroller, and a third only needs a 555 timer, and maybe a fourth an LED or something. Doing this will save you time, effort, and money in the long run. While it can be arduous and mind-numbing to do, if you truely want to be successful you will do it.

This isn't to say you have to go this route; but sooner or later you will find yourself in this position, and it is better to have a handle of some sort on it beforehand, rather than finding out years down the road that all of the processes have grown "organically", and no one understands what is going on or how anything works, then you have to reverse engineer everything already accomplished just to understand how you got to that point - and then you find out where the problem lies because your process maps and flowcharts look like the squiggle from "The Dot and the Line"...

What I wrote above applies equally to processes and problems like a circuit design, a piece of software, a building, a corporation, or a country and its government. Unfortunately, humans in general are all-to-poor at proper planning like this (and it shows).
4986  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: why should I use a H-Bridge on: March 10, 2010, 04:25:08 pm
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The trick is not to have inputs that you can put in that way, so on a simple level this means having only one input and taking the inverse of it to drive the other half of the bridge. Look at a chip like the UC2714, the data sheet has a block diagram of the sort of thing you need.


So basically the two inputs become "direction" and "enable", instead of two logic inputs, right? Guess I have a small amount of redesign to do, then - but no problems...

 smiley
4987  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: why should I use a H-Bridge on: March 09, 2010, 10:39:39 pm
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So half the batteries drive it forward and half of them backwards. It doesn't make for a very even battery usage. You end up changing them all when only half are discharged.

Yeah - this was a problem with it; but it shifted the extra cost to the user, away from Milton Bradley...  ;D

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Can't see why you say that if all LEDs are on there is still a short through the transistors of the bridge.

Ok - so how do you design a "safe" h-bridge such that no matter what the inputs are, there isn't a direct short? That is the question I would like to see answered - that, or how do I ensure that the outputs of the Arduino are always in the "safe" position? Right now, my only answer to the question is to delay the power-up of the h-bridge until I am certain the Arduino has everything set properly (via some kind of "enable" pin or something), coupled with a fuse on the power supply rail feeding the h-bridge.

Seems kinda like a hack.

 smiley
4988  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: why should I use a H-Bridge on: March 08, 2010, 06:30:16 pm
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without an H bridge you can only control the speed of the motor in one direction

Actually, on the Milton Bradley Big Trak, they used a weird "half h-bridge" design with a dual ended power supply; only two transistors used per motor.

Regarding h-bridges: on another thread, someone mentioned that using only NPN transistors for such a bridge could be a bad design; it wasn't said, but I got the gist that it was better to use NPN on one half, and PNP on the other. I have designed an h-bridge using 2n3055 NPNs (TO-3 cases), but after hearing that information, I looked into other designs - I found this:

http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-circuit.html

If I used the 2n3055 complement (MJ2955) for the other half, is this really a better design? It seems safer (ie, no possibility for SEDs/FEDs), and would allow me to implement coasting and braking (something I can't do with only NPNs?).

Am I looking at this wrong? Is there a way to use only NPNs and still get the safety from shorts? I am already using opto-couplers, and only drive one half at a time - but if both halves are high, fireworks (I imagine!) could appear...

Is an NPN only h-bridge safe, or -must- you use complementary pairs? If I have to re-design, no big deal - I am just looking for some feedback (PM me if you want).

 smiley
4989  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: store to buy sensors on: March 04, 2010, 01:20:33 am
Thanks for the links and such, digitalman2112; I guess $5k is cheap when you're looking at $75k. It also says I am in the wrong line of work.

The music video was pretty cool. Thanks again - I always like getting introduced to new music...

 smiley
4990  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: store to buy sensors on: March 03, 2010, 12:14:21 pm
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Since $5585 USD is "affordable", I wonder what their idea of "expensive" would be?

That's pretty funny; I knew these sensors were fairly expensive, but I never realized they were multi-thousand dollar devices:

http://www.hokuyo-aut.jp/02sensor/07scanner/utm_30lx.html

It doesn't say whether it uses angular measurement (triangulation with 2D cmos sensor array), or 2D time-of-flight (LIDAR); with that price I would guess the latter (basically working like an ultrasonic distance sensor, just at a much higher speed, timing the flight of the laser pulse for distance measurement), but maybe not?

I'm hoping for my robot project to implement a cheap multi-point-grid webcam-based LIDAR system (using OpenCVS most likely); maybe if somehow I get funding I can afford some of these more fancy toys!

 smiley-grin
4991  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Why does my resistor have no effect? on: March 03, 2010, 02:50:28 pm
If you need more than 1 amp, and all you have are 78XXs laying around (and are cheap and lazy like me!), you can parallel the lines together for higher amperages (I would only 2-3 like this, honestly - it would get absurd after that).

 smiley
4992  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Why does my resistor have no effect? on: March 02, 2010, 10:45:23 pm
If you want to get the full 1 amp rating for the 7805, you -must- mount it to a heat-sink (unless you like having smoke/fire-emitting devices around!)...
4993  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Multimeter on: March 02, 2010, 04:31:04 pm
Personally, I've never had a problem with the el-cheapo meters from Harbor Freight (discount chinese tool vendor); they tend to last for a fairly long time, they handle light abuse, and the batteries are typically standard 9V.

Not sure how you would be able to tell if there were an issue with one, unless you already owned a quality meter (Fluke or such), then you could probably compare readings...

 smiley

/not a professional
4994  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is this right board for connecting sensors to a PC on: March 02, 2010, 04:36:33 pm
Also - keep in mind that depending on the tank, usage, and local/State laws (whatever that means in the context of your geographical location), modifying or even attaching such a device (without being licensed, etc) may violate laws; check into this before attempting any such modification, and if in doubt, ask a professional.
4995  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Batteries on: January 31, 2010, 05:08:29 pm
If you are planning on running on the on-board regulator (say via the external voltage jack), then you are going to need at least 6 volts (you can go all the way up to 12 volts, IIRC); or 5 1.2 volt NiMH cells wired in series (here is where going with a standard R/C car 7.2 volt NiMH pack makes sense; tons of current available, and easily within the spec for the on-board regulator).

 If you are going to bypass the regulator (as noted by koyaanisqatsi) by connecting to the 5V input pin on the Arduino board, then a 3 or 4 cell pack (3.6 or 4.8 volts, respectively) would work fine; just note that without a regulator, once the battery voltage drops below 3.6 volts, "strange things" will occur (everything from wrong readings on analog pins, spontaneous resets, to just turning off). Also if there are other loads connected to the battery, their power needs may cause the voltage to fluctuate to the Arduino, which could cause similar strange issues; the purpose of the regulator is to deliver the exact voltage needs, regardless of the level of the input voltage (within certain parameters, of course).
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