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46  General Category / General Discussion / Re: Describing a "Cube" on: June 21, 2014, 11:01:08 pm
afraid people can't grasp the implications of a "27 pixel cube"?

Maybe you are better than math than me, but I would be sitting there for a second thinking "ok, what's the cube root of 27?" or "what's the cube root of 125?"; and as the number became larger...well.

Maybe, rather than "3x3x3" or "5x5x5" - calling it a "3 cube" or a "5 cube" or an "n-cube" - would be the better option? Conveys the size needed per side, and no difficult factorization needed...

smiley-grin
47  Using Arduino / General Electronics / Re: H-Bridge with High Current Transistors on: June 21, 2014, 11:08:55 am
Perhaps the easiest way to build an H-bridge from discrete components is to start with
good MOSFET H-bridge or half-H-bridge driver chips(*), add 4 n-channel MOSFETS
well up to the power and current and voltage ratings, and follow the suggested circuits
in the driver datasheets.  If you have a supply of limited current-sourcing ability
that will help prevent expensive mistakes (lead-acid and lithium batteries are not
forgiving).

I'm going to second this, with the following extra bit: Size the FETs 4 or 5 times larger than your current needs (so you want 10A - pick 50A n-channel FETs). That will give you plenty of breathing room, and it won't be that much extra to spend. You likely won't need heatsinks for a FET h-bridge (with the larger FETs and the smaller current needs), but you might want to leave room for them just in case (or if you want to use it with even larger motors later).

That said - you would still likely to be better off purchasing an h-bridge; since you don't want to go down this route, purchase plenty of spare FETs for the inevitable destruction as you test and play with the h-bridge you do build.
48  Using Arduino / General Electronics / Re: Perf board wiring, solid core or stranded? on: June 21, 2014, 11:01:26 am
Used wire wrap years ago. Thinking of doing it again for a few prototypes. RS used to carry it in the stores, but no longer. Have to buy online. If anyone finds it at a good price, let us know.

The thing I hate about wire-wrapping is the cost of sockets, plus the fact that if you don't do things "just right" (and even sometimes if you do), and you find a bad connection during testing - you may have to unwrap multiple layers to fix the wire you want (then re-wrap, which may introduce further bugs).

Yes, solid wire for perfboard. I use telephone wire as it is cheap. Sometimes I can find it in the dollar store for 25ft. However I have to strip the 4 wires apart first.

My favorite (mainly for breadboarding - but in a pinch can be used for perfboard) is 25 pair telephone cable. I typically look for it at ham fests; sometimes you can get it from older offices during a remodel. 8 feet or so can last you a lifetime (especially if all you need it for are jumper wires).

Another potential option (though not great) is to use solid-core ethernet cable; 8 wires and "colors" - and can be found all over the place (again, office remodels are a great source - or ask the guys in your IT department, if you work in place with one).
49  Using Arduino / Motors, Mechanics, and Power / Re: Powerful DC motor to Servo motor on: June 18, 2014, 08:57:21 pm
A popular setup, but the servo does not necessary need to be physically attached to the wiper arm, just the pot will do.

A couple of more links:

http://www.webcomsknkwrks.com/mowers.htm  (scroll down a bit - part of the article details "monster servos")

http://www.modifiedpowerwheels.com/forum/topic.asp?TOPIC_ID=13458

http://www.instructables.com/id/Build-a-HUGE-RC-MONSTER-TRUCK-Golf-Cart-Wheels-/step6/Heavy-Duty-Steering/

Basically, you take a servo, and remove the motor from the control board - then you solder wires from the control board to the control lines of your (larger, high-power) h-bridge; provided that the control lines on the bridge are 5 volt tolerant, and you supply the servo with 4.8-5 volts - it should all work fine. Then just remove the remaining gear train from the servo, but leave the potentiometer in place. Attach a servo horn and connect that horn to your moving bit. A little tuning and debugging, and it should be good to go.

While zoomkat is right in that you don't need to keep the servo intact - you do need to keep the potentiometer (or one of the same type and size) connected to the servo board for this to work. That said, I would personally keep everything in the servo case, for a number of reasons:

  • The case will protect the electronics and potentiometer (especially if it was a "waterproof" servo)
  • The case will provide the support for the board and potentiometer
  • The case has convenient (and standard) mounting holes (and convenient/standard servo horn)
  • And the biggest one: The potentiometer shaft and such will be supported by some form of bearing to prevent side-loads from the horn being rotated externally from causing additional mechanical wear
50  Using Arduino / Project Guidance / Re: arduino code for L298n (serve as a switch) and peltier device/module on: June 16, 2014, 12:14:38 am
hi I would like to know how do i go about doing the arduino code for my project on peltier module. basically i would need to link up a L298n H-bridge to the arduino

Stop right there.

You didn't mention -which- peltier you were trying to control; this is an important piece of information for you to be successful. For instance, let's take a look at this peltier/heatsink combo from a well-known Arduino supplier:

http://www.adafruit.com/products/1335

Note the specs - it requires 12 volts at 5 amps.

An L298 - if you are lucky and have one helluva heatsink on it (with forced-air cooling) - is rated to provide up to 4 amps of current to a single load (provided you have wired it to operate in "parallel mode"); in practice you'll be lucky to get anywhere close to that.

Your peltier may draw more amps, but I doubt it would draw fewer - peltiers tend to be high-current loads, and many pull 8-10 amps or more.

In short, you likely have the wrong driver for your load - but until we know which peltier you have and what it's voltage/current requirements are, recommending a driver will be difficult at best.
51  General Category / General Discussion / Re: Question about posting creating a certain topic. on: June 08, 2014, 12:53:11 pm
Is there no other place where people share code, programs etc..? And for example tutorials?

The problem I am seeing here (correct me if I am wrong, though) - is no mention or connection with the Arduino. If it doesn't have at least some kind of use with the Arduino, it won't fit into any topic here, besides this one (General Discussion) and/or maybe "Bar Sport".

If it is, as you mention, only an "Xbee API compatible (with) Java" - actually, I am not even sure what that means...

Do you actually mean it's an API to communicate with an Xbee, written in Java? If so - then it certainly is more general than the Arduino, I would think.

Unless you have an Arduino project (connected to an XBee), and it acts as a part of the whole system; in that case, it would go into the Exhibition topic - but even there, it would seem that the Arduino portion is only incidental.
52  Topics / Robotics / Re: Using invisible dog fence as boundary for lawn mower robot on: June 08, 2014, 12:46:36 pm
Good thinking
May be a add-on for my mowrobot later.

I've been thinking about this (border/non-grass detection) for a while, ever since acquiring a Friendly Robotics RL-500 mower for $50.00 USD off a local guy on craigslist; I swear that one day I am going to get it running again...

My thing is that I am a very lazy person - and I don't want to dig and bury a powered "border fence" - so I have been contemplating a ton of alternatives.

One involves magnets and hall-effect sensors. Basically I would mold small rare-earth magnets into plastic golf-ball tees, and spike them along the edges and other no-go areas. Mount hall-effect sensors on the mower platform, and let it detect them. Passive, cheap, easy to replace.

Another option was to detect the presence of grass in some manner. I've thought about the idea of a humidity sensor, maybe coupled with a color sensor (or something) - to detect mowed vs. unmowed (vs non-grass) areas. Such could also improve a "random-walk" algorithm to be a bit more efficient.

A third option (by far the most ambitious) was to add some kind of custom LIDAR unit (for SLAM - so the robot knows where it is and where its been), plus a form of machine-learning via OpenCV to detect vegetation vs non-vegetation. I've seen some papers on how this is done (vegetation detection, that is) - replicating it would be very difficult, but in theory possible at a hobbyist level. Provided I spent the time. Again, laziness. Lol.

Likely, a combination of all of the above methods would be needed to make it work somewhat well. It likely would still need to be baby-sat as it worked (better than doing the work yourself, but still not fun here in Phoenix in the summer!). And, it still wouldn't trim the bushes or trees for you.

I currently pay a maintenance outfit to do my front and back yard every couple of weeks for $60.00; honestly, it's a bargain.
53  Using Arduino / Motors, Mechanics, and Power / Re: half stepping l298 on: June 08, 2014, 12:33:11 pm
The L298 is not designed to control steppers.

I take it you haven't read the datasheet?

Unless you are meaning "driving" is different from "control", then I can give you that; the L297 (companion part to the 298 for stepper "control") is the part needed...
54  Community / Bar Sport / Re: Linux instructions on: June 07, 2014, 01:14:08 pm
Have you noticed that a lot of instructions on how to do things in Linux are a bit like this picture:-

What I have found in my years of linux (been playing with it since 1995 or so) has been either instructions/tutorials to solve an issue tend to be extremely dense (verbiage, or just a lot of steps, or both) - or that they feels like a LISP program (at every turn, there is something different to do, nested lower - and in many cases a lot of dependencies to fight over until it comes back together at "the top").

Yes - sometimes I have run into the "draw an owl" scenario, but more often than not, the above two scenarios seem far more common to me.

Not that I mind - in fact, I enjoy it to an extent. I look upon it as a puzzle to solve - and most of the times I manage to get it figured out (often forgetting why I was there in the first place!). Part of it stems from my personality (and/or lack thereof), but part of it had to do with my masochism of one of my first linux installs a long time ago:

Turbo Linux 2.0 on a 486 laptop with 8 meg of RAM; I had to learn not only how to install it, but also how to re-compile the kernel in order to get the sound card, PCMCIA slots, and other peripheral devices all working properly. Ultimately, I got it done, but not without a lot of reference to man pages, the internet (over a modem back then), and more than a few books.

If that didn't scare me away, nothing will (actually, I had a small amount of prior Unix experience under my belt, so I wasn't all that unfamiliar with the "density" of *nix)...
55  Community / Bar Sport / Re: Linux instructions on: June 07, 2014, 01:05:39 pm
For the love of... I just want to know how to synchronize the system clock to my time server on boot-up...  smiley-cry  This has got to be a common scenario!  I could've written my own driver by now!

Also, honestly - this doesn't look that difficult (mind you, I've never tried):

http://www.akadia.com/services/ntp_synchronize.html
56  Community / Bar Sport / Re: Linux instructions on: June 07, 2014, 01:02:20 pm
I've found man pages come in two lengths

If you want a real fun one to read, check out the man page for "sudoers" (ie - the list of sudo users, more or less).

That file has a particular "grammar" behind it, described in something called "Extended Backus-Naur Form (EBNF)"; because I imagine most people have no idea what that means, the author of the sudoers man page decided to stick a "Quick guide to EBNF" in the middle of the man page.

It's not that it is long, it's just that it is weird and dense - a strange little bit in the overall landscape of *nix...

smiley
57  Topics / Robotics / Re: Using invisible dog fence as boundary for lawn mower robot on: June 07, 2014, 12:50:42 pm
Have you tried using the receiver portion of a cheap "wire-tracer" tool - example:

http://www.harborfreight.com/cable-tracker-94181.html

Such a device might be able to pick up the signal that your virtual fence transmitter is outputting, and you could then use the presence of that signal (and/or the strength) to determine where your robot is in relation to the boundary wire.

Might be worth purchasing and trying it out - worst case is that you are left with a wireless signal tracing tool (which are pretty useful on their own for tracking problems with wiring you can't see easily).
58  Using Arduino / Motors, Mechanics, and Power / Re: L298N driver problem on: June 07, 2014, 12:44:44 pm
I already tested the driver without arduino and voltages on both branches are approximately equal.
If proximity sensors are disconnected (or even connected, but do not write anything about them in code) on each branch have the same voltage (measured with measuring device). If I connect them (or write something in code related to them) appears the difference in voltage between branches

I wrote up a longer reply about the batteries, voltages, hookup, etc - but I think I see your problem now (maybe):

STOP USING PIN 1 as an output!

If you plan on using pins 0 and/or 1 on the Arduino, these serve the serial I/O for the USB serial interface. You can use them, as long as you don't plan on using the USB. Otherwise, you can't use them.

I think what is happening to you is that in your code, you have pin 1 (transmit) set as an output for the motor driver (for one of the motors). Everything else is hooked up to higher number pins, so they are ok. But that particular pin is being used to set (partially) the direction of the motor control for one of the motors (or something like that).

Now - at the same time, you have the sensors hooked up and sensing. In your code, when they do that, you also do some serial printing, which outputs (aka - transmits) from the Arduino to the PC - and guess which pin that toggles?

Yep - Pin 1 is then toggled - which is likely causing that motor to run strangely as the sensors work. I would bet that if you removed the serial printing from that code (or better - move the function of pin 1 to another higher pin) - everything would start to work better.

That's just my best guess, though. Good luck - hope it works!

smiley-grin
59  Using Arduino / Project Guidance / Re: Is there an easy way to create a better waveform then always on or always off? on: June 07, 2014, 12:18:06 pm
Crude PWM+filter won't make that waveform tho.

What about an R2R ladder DAC? Just throwing it out there; I'm not knowledgeable enough in this are to really know...

smiley-grin
60  General Category / General Discussion / Re: Arduino's box textures on: June 01, 2014, 05:33:35 pm
I don't know if it would be legal to use it - but it seems simple enough that you could just create your own. Seriously, I could probably spin out this pattern (well, something similar) given a few hours in inkscape...and I am anything -but- a graphics artist. Give it a try; you might be surprised by what you create...
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