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4966  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Robot: problem with load current on: March 17, 2010, 11:34:00 am
I think it might be a british thing!

 smiley-wink

I've never seen such a battery - looks to be as big as a some SLAs!

For the OP:

Make sure you get the right charger for your battery; LiPo batteries can be dangerous fire-emitting devices otherwise!
4967  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Best place to get breadboards online? on: February 24, 2010, 01:55:35 pm
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Ebay from Hongkong. I have one of these:

The boards on that one look like what TBAr noted earlier about the boards at AllElectronics; you get what you pay for. If you are a poor student, or don't mind replacing your board every now and then, they are probably a pretty good deal.

But, if you are like me and expect your tools to last 20+ years, you will buy quality (Elenco) and spend the extra money. Like I said before, that breadboard I got was an Elenco, and that was in 1991 (almost 20 years ago); other than a little discoloration from use, it still works perfectly. I have no doubt that the large version I got as a gift will last just as long.
4968  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Best place to get breadboards online? on: February 18, 2010, 11:40:30 am
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*mouth waters* Man...I'd love to have one of those.  But $30 seems a bit much to spend on a breadboard


TchnclFl: That's what I thought, too - I had eyed them every time I went into Frys; I remarked this to a friend, a few months later he bought me one for my birthday (thanks again, Jared!). I later purchased a large set of the straight wire jumpers.

I wish I had bought one sooner. It is well worth $30.00...

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That Elanco breadboard is nice. I've used it. But where do you put the Arduino?

RoyK: Good question, and I like your answer; in my case, I hadn't owned my Arduino for very long, and it was slated to be the controller in my UGV (unmanned ground vehicle) plans, but I may have to change some ideas I have about my "future" lab workbench.

I've got some massive cleanup I need to do in my shop (waaaay too much clutter); after that is done, I am going to build my workbench up properly. I have this old (but I think working) digital trainer box thing, that has a small breadboard, a power supply, some leds, a low-frequency waveform generator, and a set of debounced switches - that I want to use to form a part of a prototyping system; I figure that by using parts of it, adding a larger bench power supply, my multimeter and a parallax PC o-scope I have (won it in a Nuts and Volts contest back in 2008) - I could have a pretty good bench. I am thinking about a system where I buy a few more of those Elenco boards, and leave the boards attached to the metal, but instead of mounting them with screws, I might use velcro or magnets (magnets and a piece of grounded steel for the backing might be nice!); if I use magnets I realize that certain circuits would have to be developed off-board, maybe (depending on how well the flux stays in the steel, things like non-GPS compass circuits or hall effect circuits might not work properly).

That way, I could remove the boards and use them individually, or combine them; maybe I might stick with the one I have, then just buy a bunch of the individual ones (although I would definitely want to buy a bunch of the bus strips separately - I know they are sold this way), but still do the attachment with magnets or velcro. My Arduino might become a centerpiece in such a case, kinda like you are saying (hmm, maybe with one of Mowcius' acrylic shields?) - I have already upgraded it to a 328, and my bootloaded 168 could be used as the controller for my system (my code is so far only pushing 5K, but I still have a servo control system to add), and I could keep the Arduino as the dev platform - although at some point I want to build or add a ZIF socket shield, board, or something to it.

Right now, I do most of my development on my Arduino inside my office (which needs its own cleanup!) in the house; I don't really like that arrangement, but it works. I am hoping to begin my shop cleanup this weekend (I am still wondering what to do with the PowerWheels H2 that sits inside; its the base for the beta platform of my UGV - takes up waaay too much room)...

 smiley-grin
4969  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Best place to get breadboards online? on: February 18, 2010, 01:12:45 am
Buy one or two of these; trust me, you'll love it:

http://www.tequipment.net/Elenco9480WK.html

I bought mine at Fry's Electronics:

http://www.frys.com/product/4612378?site=sr:SEARCH:MAIN_RSLT_PG

Cheaper, too - this Elenco model is almost "the cream of the crop" when it comes to breadboards; the individual breadboards used in it are the same as that pointed out by TBAr earlier:

http://pjrc.com/store/breadboard.html

It also has 4 binding posts for power needs, with 4 colors (mine had red, black, green and yellow binding posts). Right now I have breadboarded on it a full 2n3055-based (TO-3 package) h-bridge with opto-coupler (4n26) interfacing, along with power and directional indicator LEDs - its easy to breadboard even with those monsters, they fit perfectly across the valley, and the large size makes it a breeze to lay out a circuit like that comfortably. Denser circuits using more normal sized parts are no problem, either. The extra power bus strips along the top make it even more awesome. Finally, the metal base (with its rubber feet) make for a very comfortable working session.

I can also attest to the longevity of the individual breadboards used; I have and still use one such breadboard that was given to me as part of my enrollment at a local Phoenix electronics school; that was almost 20 years ago, and the thing has held up well over those years.

I am seriously considering buying 8-10 of those boards, getting a nice piece of sheet steel or aluminum, and making one awesome breadboarding lab station; something like that, with built in easy-connect debounced switches, LEDs, maybe an LCD, power supply, waveform generator, etc - the ultimate adult ###-in-one electronics kit.

One of these days...

 ;D
4970  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: USB Device Project - Right for Arduino? on: March 16, 2010, 01:19:35 am
I'm a q&d kind of guy, I guess - just grabbed the first thing I saw; I would hope the builder of the circuit would verify things. I guess I shoulda looked closer; most of the time it seems you can't find 5VDC 4PDT relays, they almost always seem to be 12VDC...
4971  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: USB Device Project - Right for Arduino? on: March 16, 2010, 12:40:28 am
Well, for the most accurate representation (mechanical insertion/removal) of this, you would probably want to use a relay - a 4PDT relay would be perfect, like this one:

http://www.allelectronics.com/make-a-store/item/4PRLY-12/RELAY-4PDT-12VDC-KH-STYLE/-/1.html

Alternatively, you could use two DPDT relays, or four SPDT/SPST relays.

Hook it up according to the numerous examples available, coding is just toggling a digital i/o pin HIGH or LOW.

Hook the usb wires up to the relay (as close to the relay as possible), and the coil thru an NPN transistor (like a 2n2222) with a snubber diode across the relay's coil to prevent kickback voltage from destroying your transistor; the base of the transistor should go to the digital i/o pin with a bias resistor (1k or so) in between.

Hope this helps. Good luck!
4972  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Controlling a motor direction and speed on: March 16, 2010, 01:17:23 am
Not necessarily, retrolefty...

He could stick another NPN between the ground and the connection junction of the NC/NO contacts; the collector going to the contacts, the emitter to ground, bias resistor on the base (then connected to the Arduino), and a flyback/snubber diode across the collector/emitter junction (I think).

 smiley
4973  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduinos IN SPAAAAACEEE! on: March 09, 2010, 10:50:45 pm
StarkRG:

You mentioned Scaled Composites; I've been to their hanger back in the day when Voyager was flying - didn't get to meet anybody important or such (it was a lonely weekend), but I had fun as a kid.

Scaled Composites DID NOT go into orbit with their launch. At best, they had a ballistic trajectory. They -barely- made it to the edge of the atmosphere where "space" begins. In no way did they have the fuel budget or speed needed to achieve orbit.

They ended up spending the equivalent of $2.00 for a 25 cent prize. I realize they were just proving it could be done, and that it was one small step. With that said, we have yet to see anybody else do it. I am not saying it won't be done again (non-orbital launch); Virgin just might do it next, or someone else. But that is still a long way from attaining low-earth orbit.

LEO is a long way away (orders of magnitude) from a moon flight and landing.

Finally - if you don't think you are going to have to answer to some government somewhere on Earth (or deal with politics) when it comes to building the equivalent of a intercontinental ballistic device - you are dreaming. Dreaming big, but still asleep.

Good luck.

 smiley
4974  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Arduinos IN SPAAAAACEEE! on: March 08, 2010, 06:21:33 pm
StarkRG:

So - is this all just some kind of "thought experiment", with some notes that come out at the end to be filed away for later for when it seems that launch prices are coming waaaaay down? Beyond that, I don't see much practical need.

If you were designing something for harsh earth-bound environments, then I could at least see the possibilities. For space-bound (and lunar-bound) devices, even if you managed to gather all of the information, then design and built a device, it would still be a moot point because it is unlikely that, within your lifetime or your children's lifetime, that the political will and technology will be there to enable ordinary people to put stuff into orbit or send it to the moon.

The energy costs alone are that huge. You should know this. Unless there is some breakthrough in energy research (sustainable fusion?), space is simply out of reach for all but large multinational corporations, and governments - and so far, only government entities have managed to put men in orbit, on the moon, and send devices to other planets, orbit the sun, and out of the solar system.

Even if there is an energy breakthrough, you still have the political issues to solve; we could loft large buildings into orbit TODAY, were it not for the lack of political will (and a pesky thing called the above-ground nuclear test ban treaty). The population gets real butt-achey about anything with the word "nuclear" in it, because they are ignorant and selfish, mainly. Too bad that the only thing that will effectively get us off this planet, and out among the stars, will most likely have to be nuclear powered.

The thing is, all of the problems you are asking about are pretty much solved. They were solved a long time ago (and the vast majority of the information regarding them is free for the asking for US citizens, because it was paid for with your parents tax dollars). You can go ahead and attempt to re-engineer them, but as soon as it does become cheap enough to go into orbit and then to the moon, those companies which have solved the problems will simply pull some plans off the shelf, build the vehicle, and launch it. They'll probably be able to do it cheaper than an individual could. Just don't expect this to happen in the next 50 years - or even a hundred.

If you are simply doing a thought experiment, why ask here? Have you researched at your library? At university libraries? Have you travelled to Cal-Tech (JPL) and did some research there? Have you looked online? The answers to your questions are all there; tons of books and papers have been written covering all of them.

Honestly, there isn't much special - for most of it, you do what you can with light-weight materials for shielding, put the rest behind certain kinds of mass/matter (lead is one, there are others), then use redundancy with voting (for the processors), as well as watchdog interrupts and such, and you still have to pray. Getting rid of radiation is mainly done with external heatsinks and a "slow roll" to even out the temperatures involved. You also need to think about dust and such (once on the moon); sealed systems, positive pressurization, etc - can help with that (but eventually, it will fail).

As others have noted, you can learn a lot just by trying to design something to deal with harsh earth-bound issues (for instance, I am constantly amazed at the design and evolution of the iRobot Roomba - the floor is a very harsh environment for a vacumming robot!). If you can get something to survive a month in your backyard without fixes or updates, your next step would be to stick it in the Black Rock desert for a year; if it can survive there, it can probably survive on the moon!
4975  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Does Arduino Mega require a motor shield? on: March 15, 2010, 02:09:07 am
What I would do is look into writing an interface control program on the Serializer to take commands via the serial interface, and control the rest of the platform. Then, interface the Arduino Mega to the Serializer. Set up the control program so that everything about the Serializer is exposed via serial commands, burn the code onto it, and leave it, never to touch it again except for debugging. Offer to those who want to migrate from the Serializer.

If you wanted to "rip" the Serializer out, though, it looks like you would need to add your own h-bridge controllers to replace what was on the Serializer; fortunately, these are well available and documented - there are several companies that make a variety of modules (Pololu, for instance) for h-bridge motor control that can be interfaced to the Arduino, and none of them are expensive.

As far as the batteries are concerned, it depends on how they are hooked up; if they are in parallel (for double current capability at 9.6 volts), then you can hook it up to the external input to go through the regulator; if they are separate (one powers the Serializer, one to the motor voltage inputs on the Serializer), then you can do the same with the Arduino Mega and whatever h-bridge driver you use. Only if they are wired in series to provide 19.2 volts will you need to do something different (lots of options are available; the easiest would be to separate the packs, unless the motors require such higher voltage; then you might want to add a split in the pack to give a 9.6 volt leg for the Arduino's external voltage input).

As far as the encoder wire is concerned, it will depend on the h-bridge; you might find one with an encoder input, but likely you would just run that to a digital input on the Arduino, and monitor that in code (it isn't what you would call a "native" support; but you might be able to find an encoder library out there somewhere - or, if it doesn't exist, you could be the first to code one!).

Hope this helps...

 smiley
4976  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: newbie, dumb question - have read - tried to find on: March 13, 2010, 02:10:00 am
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It's just going to take me awhile to review what you said, but yahoo! so now we can do embedded ourselves, what a great state the technology is at.

It's always been possible for a long time for hobbyists to do embedded CPUs in their projects; it hasn't always been cheap, but it has been possible. For instance, a 6809 CPU board (or a Z-80 board, for that matter) is fairly easy to design and connect up, only a few support chips are required (typically the cpu, some memory, and some control logic for the bus; plus clock, eproms, etc).

What has always been difficult was programming the beast; early (mid/late 1970's thru early 1980s) embedded designs, like you saw on early hobbyist robotic designs (as presented in old TAB books), typically used toggle switches to hand-assemble hex codes for the assembly instructions into each memory location (basically this was the design of the Altair and other early S-100 bus computers of the 1970s).

There were other ways of getting code into these systems; typically involving EPROMs that only held a few K of code, and using a special programmer (which tended to be relatively expensive) to dump the code into the chips, then they were read by the CPU at boot time. Serial monitor software and BASIC interpretors were common.

When the 8051 came out, it was like a sea-change; there was finally a system cheap enough and could use standard C compilers to create code with; it opened up a lot of new ground. Then the PIC came along, which revolutionized the whole electronics scene (shifting it from using discrete components to blink an LED to using a small microcontroller to do the same thing, and more).

Mainly it was a cost vs ease-of-use thing; today we have very cheap microcontrollers that are more powerful (in some ways) than early personal computers, and cheap (free) tools to create code and easily upload to the chip (so no need for special programmers or such).

It really is a very interesting time to be alive and experiment with this technology! We've come a long way just in the past 15 years; the next 15 years may just prove to be amazing...

 smiley
4977  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: newbie, dumb question - have read - tried to find on: March 13, 2010, 01:56:27 am
Here's the thing, though - inserting and removing the ATMega chip from the Arduino can be difficult (like all socketed DIPs); use a  small flat-blade screwdriver (not the jeweler kind; you want one that looks like a regular flat flared-blade screwdriver, only tiny), slip it under one end, and twist it a little side to side, put it in a little more, twist a little, and keep doing this until is it fully loose, then you can pull it free fairly easily.

Putting in a new ATMega will require you to slightly bend the pins inward on a flat surface (they also make a tool for this) - this is because fresh from the factory the pins are spread out a bit, and are very difficult to insert into the DIP socket without potentially bending one or more pins.

If you plan on doing this kind of task more than a few times, you might want to consider building a ZIF socket shield for programming bootloaded ATMega's; examples of such a board can be found on the arduino.cc site (I think in the playground?); SparkFun also has an example of such a board.

Basically, it is a shield (a protoboard shield PCB should work perfectly; in many cases you also have a reset button and LEDs on the shield as well, which are both very useful to have) in which the pins brought up by the headers are connected to the appropriate pins on a 28-pin ZIF socket to match the ATMega8/168/328 pinout. You have to then supply your own 16 MHz resonator/crystal, plus the loading capacitors (18-22pf), because the crystal connector pins on-board the Arduino aren't brought up via the headers. Remove the ATMega from the Arduino board, install the custom ZIF shield, then install the ATMega into the ZIF socket; the board at that point should work as it normally did, but it will be much easier to swap out bootloaded ATMega ICs for programming at-will.

So far, I haven't found a vendor of such a shield anywhere, so it is currently still very much a DIY project...

 smiley
4978  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: newbie, dumb question - have read - tried to find on: March 13, 2010, 01:34:16 am
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Is it possible to program a chip with the arduino, then disconnect the arduino and just have the chip run by itself?

I am going to make an assumption here, and assume by "chip" you meant the ATMega168/328 that is on the Arduino board, correct?

So, you are asking "is it possible to use the IDE to program the ATMega168/328 (with bootloader) on the Arduino board, then power down the board, remove the chip, then put it in something else, and have it run?".

The answer to that question is "yes" - there are a few extra parts needed if you want it to continue to run at 16 MHz (otherwise, you just need to supply 5V and ground, and the internal clock running at 1 MHz will be used - some timing related code will be affected, I believe); these parts are mainly the 16 MHz resonator/crystal and 18-22pf parallel loading capacitors (all of which are very cheap). If you want to continue to be able to program it (in-field programming), you can supply a set of header pins for rx/tx and use an FTDI cable, or you can supply an ISP header and use an ISP programmer to upload the .hex file of the compiled sketch.

Is this what you were asking?

 smiley
4979  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Servos vs DC Motors? on: March 13, 2010, 10:16:53 pm
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Well, from some of the replies, I'm baffled because if you go to Adafruit you can get a continuos rotation servo.

These are standard servos which have been modified in some manner to allow continuous rotation; using the term "servo" with these is kind of a misnomer, as they are no longer servomechanisms, but rather gear motors with a built in controller for direction of rotation dependent on a specific PWM signal for command input.

It used to be that you had to modify a servo to get it to continuously rotate, but now some manufacturers sell them pre-modified (they can be useful in certain R/C contexts), or vendors modify them and then re-sell them as modified.

I have never ordered from them, but they seem to offer very cheap servos (not as cheap as direct-from-china ebay sellers, but almost as good), plus a lot of other hobby R/C parts:

http://www.hobbycity.com/hobbyking/store/uh_index.asp

These guys are expensive, but they offer some interesting higher-power servo solutions:

http://servocity.com/index.html

 smiley
4980  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Cheap, small , project boxes on: March 13, 2010, 08:51:33 pm
I just bought a small clear plastic box today at Staples (an office supply store); it was an impulse buy - I was walking around the store when I spotted a display filled with small plastic boxes. I remembered this thread, and...

I found one that was a little larger than an Arduino - it can easily hold the Arduino and my prototyping shield together; I've only done a test fit, but it looks like you would have to put the Arduino in a far corner of the box in order to be able to drill/cut holes for the external power supply input and the USB port; I might play with it some tonight if I have the time after I work on cleaning my shop.

It cost $1.79 US.

They had one that was smaller, but I wasn't sure the smaller one would be able to fit an Arduino inside. They had another with the same footprint as the one I bought, but about twice as tall (you could probably stack a couple more shields on and it would still fit - I think it was the .3 or .7 litre version). Several other sizes were also available. They were all fairly low priced.

They were made by this company:

http://www.reallyusefulproducts.co.uk/

Mine is the "0.2 Liter - Small business card size box"; it looks like these:

http://direct.hobbycraft.co.uk/Prodimg/294764_1_zoom.jpg

...but it is clear with blue snaps. It feels pretty sturdy, and has reinforced corners (its kinda molded like a small milkcrate). With the lid and snaps closed, it is a surprisingly sturdy box. I also just noticed another thing: if you look at that photo above, notice the holes on the snaps? There are corresponding holes on the box lid; you could easily use four small machine screws to secure the lid down! Pretty neat, huh? Its almost like they designed it to be used as a project box! In fact, it seems like all of their boxes are designed in this manner...
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