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4906  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Electrical connections to a rotating part? on: May 24, 2010, 04:52:47 pm
I once saw something similar to Grumpy_Mike's design, but for transferring signals to/from an ROV; the tether was on a winch device, and thus the slip-rings were needed. The guy wrote (this was on a web site that I can't find anymore) that it worked well, with no noise in the video circuit.

I think if I were going to be processing signals, though, from a sensor, I would do it with wireless, and only feed power through the slip-rings; you would probably need to have a capacitor in there somewhere to store a charge for transients and noise reduction on the power-rail, and use some kind of carbon or graphite brush (like is used in certain electric motors).

I am just thinking this because of potential noise issues creeping into the signal from the sensors that may or may not be easy to filter out.
4907  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: 17 endless pots, 17 little lcds on: May 25, 2010, 07:04:44 pm
1) there is no such thing as an "endless pot" - but there are rotary encoders
2) tiny LCDs - not sure what you want, but I've never seen them; maybe you could use multiple multi-line LCD displays instead?
3) you may have more i/o than the Arduino can support - even if you were using pots, you would still need something like a multiplexer chip or something to read them all; but since you want it endless, you need to use rotary encoders - but you can't easily multiplex those, so...?

You may need to buy a Mega - maybe someone here has a better solution...?
4908  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is a motor a generator? on: May 23, 2010, 10:37:11 am
However to be a little bit picky, if I undestand the article right you have to modify a little bit before it works. So my initial statement is not completely wrong?

I suppose if you consider adding running capacitors in parallel across the leads a modification, then perhaps "yes"?

However, some induction motors (with the exception of smaller shaded-pole motors, which work differently than a standard induction motor) already come with a running capacitor, but some don't I suppose (it depends on how and where the motor is mounted, the cap is typically physically large, and may be mounted to a frame or something separate from the motor). You may also have to remove the starting cap (and/or change the switchover mechanism).

The induction motor I have had a small starting/running cap arrangement built into it (somewhere on it), but if I were to use it for power generation, I would likely replace these with something larger, just for safety.

As far as shaded pole motors are concerned, which are induction motors as well - I guess we should probably say that "some induction motors" can be converted to generators. Most of the induction motors in a house will be of the shaded-pole variety (small fans, as well as ceiling fans and the like), but other induction motors which do use starting/running capacitors can be found in places like a refrigerator (but this motor is built into the compressor, so not as easy to pull out for use as a generator) or an air-conditioner (generally 2 or 3 induction motors there).

I'll give you this one, if you give me mine!

4909  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is a motor a generator? on: May 23, 2010, 09:57:46 am
Example of motors that can not be used as generators: induction motors


I've got an old AC induction gearmotor I pulled from a copier out in my shop that works fine as a generator if you spin it; one the only reasons why I kept it - well, that, and it was one powerful gearmotor (and a strange story about how I managed to get the copier home after finding it out in the middle of the desert).

4910  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is a motor a generator? on: May 23, 2010, 01:38:25 am
im not even going to reply, it might excite cr0sh and make him into a generator, man that much hot air could power a small city, does it matter if it's Arduino related?

At least I was able to give a reply that not only helped to answer the question, but perhaps could be used to learn to ask better questions in the future.

4911  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Is a motor a generator? on: May 21, 2010, 11:06:52 am
Actually, while a stepper motor will show "electricity being generated", from a wind-power standpoint, its actually not the best motor-turned-generator you could use.

For one, most steppers have enormous amounts of cogging to be overcome, which translates ultimately into lost energy. Secondly, one has to then figure out how to take the voltages generated from the windings, and turn them from n-phase AC signals (which may or may not look like a good sine wave!) to DC signals; if it were a single phase AC signal (of any shape) it would be easier, but because all steppers have multiple phases, to use one most efficiently as a generator (once again, discounting the cogging issue), one would want to use all phases of the motor to draw power from, and converting such phased AC signal into a DC signal won't be easy (or inexpensive).

There are better and cheaper options for wind power, anyhow. Probably the easiest and cheapest is to pick up an automobile alternator from the junk yard (preferably an AC-Delco unit without a voltage regulator). Such alternators are designed to charge 12 VDC batteries; bypassing the regulator allows you to insert your own proper charge controller - but even if you can't purchase (or modify) one so it doesn't have a regulator (many current model vehicles use regulators in the alternator that are "built in" and generally difficult to bypass - though it can be done if you have the tools and time), you can still use it as long as you can get it to rotate at the speed an engine during normal driving would spin it (several hundred or more RPM generally).

The next best form of a generator that can be had cheaply are certain single-phase AC motors. Depending on when they were last used, they will have a residual magnetic field left in the rotor, that, when spun, can feed back into the stator (cutting lines of force, etc) and generate electricity. If it doesn't work right away, sometimes you just run it as a motor briefly, then it will work again. Several sites on the internet detail how to turn such a motor into a generator, as well as how to properly turn the signal (which, when properly combined with the right wiring setup and a certain sized capacitor, will give you approximately 50-60 Hz single-phase AC) into a DC voltage for charging a battery bank.

There are tons of methods of converting motors to generators; of course a motor can be a generator, and a generator a motor - Michael Faraday proved this almost 200 years ago; this is EE101 (if that; one should have learned about Faraday by about age 11, IMHO). You can find tons of information on wind power and how to homebrew it on the internet as well as from tons of books (most written in the 1970s, actually, during the "earth day" and "oil embargo" years).

What is the point of this question anyhow, now that I have exhausted it enough? Is there something in this Arduino related (I suppose one could use an Arduino in a charge controller or phase convertor system)?
4912  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Program two 328's at once? on: May 20, 2010, 02:03:09 pm
ISP is far superior.

Would you say it is better to use a dedicated ISP programmer over the Arduino ISP sketch? Or is the sketch "just as good"?

I recently bought parts for a ZIF-based holder/programmer for some bare DIP ATMegas (168/328) that I have (well, they're bare in that they aren't part of an Arduino board; they have bootloaders on them, though) - I was thinking about making a jig to hold them for quick programming for later "embedding". If I could set things up to use the jig both in an ISP programming mode and bootloader programming mode (by tapping off the Arduino properly), that would be interesting and likely useful...

4913  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Program two 328's at once? on: May 20, 2010, 01:48:53 pm
If something goes really wrong you can brick it even without a programmer. Unless you start messing with the fuses there is no higher chance to "brick" it. If you have a HV programmer (or some Arduino around) you can "unbrick" it again.

As long as there is a way to unbrick it - I haven't had a need yet to program an ATMega in this fashion, nor does ISP programming scare me (although I would need to study up on it a bit before I tried); but it is nice to know what could possibly go wrong, and that there is a potential means to reverse the problem. Thanks for the info!

4914  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Program two 328's at once? on: May 20, 2010, 01:02:47 pm
No, you upload through the ISP. No need for a bootloader. It will completely bypass the bootloader.

Ok - this is what I thought; you essentially will end up "overwriting" the bootloader, then, right? But you gain back the extra 2k. Also, isn't there an inherent risk in doing this, in that if something goes wrong (you lose power, a cable is disconnected, etc) - that you can "brick" the chip (not sure if you can get around this in some other manner or not)?
4915  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Program two 328's at once? on: May 20, 2010, 12:10:00 pm
actually it will be not more complicated if he tells the IDE about the new programmer. That is if he modifies boards.txt accordingly.

So you can upload via the bootloader through the ISP (using the upload button) using an ISP programmer (Arduino or otherwise), provided everything is configured properly? I thought the ISP was just for direct hex/binary uploads (like putting a bootloader on)? I haven't researched this much, as you can tell!

4916  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: Program two 328's at once? on: May 20, 2010, 11:59:31 am
I'm not going to be programming it millions of times so I don't mind the host 328 getting reprogrammed along with it, even if it is a waste. It saves me taking any chips out and breaking pins on them which I've already done once.

I don't know if this would work though. I can't see it not working without the duemilanove 328 in the 'host', but with the 2 chips, would that work?

I think your main issue might be current limitations of the FTDI chipset; you might want to look into that. With that said, if there are limitations to doing this, you could possibly set up some kind of buffering system to supply the current needs.

But at that point, it would probably be cheaper to install a header and buy/use an FTDI cable.

Your cheapest method might be to install a header for ISP programming, and use the Arduino you own in this manner (as an ISP programmer - there's a sketch for it on the playground, I think - I think it is also included in the examples folder); of course, that makes things a bit more difficult than simply clicking "upload" in the IDE.
4917  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: What shall I make? on: May 18, 2010, 05:14:51 pm
If you haven't played with the examples, I suggest you start there first...
4918  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: linux on arduino? on: May 20, 2010, 04:53:07 pm
This sounds like a challenge...

Let me know how converting a 32-bit codebase to 8-bits works out (I am not saying it is impossible, just that you aren't appreciating the scale of what you are proposing!).

Is there any way you can increase code memory for the arduino?

AFAIK, no.

There is also the tiny matter of having to deal with the Harvard architechture of the device, which wouldn't be a big deal if SRAM was much, much larger. You could potentially use an SPI serial eeprom device, or serial RAM - to make up for the lacking space, but you would have to write your own drivers (or hack the standard C libraries to support them?) to utilize the extra room for data. This would be just to gain extra area for variables, arrays, and such. You would want to add a filesystem (or something similar) on top of that too.

Your best bet, if you are serious about such a thing, would be to look into how old 8-bit operating systems were created; popular ones of the period were CP/M, OS-9, and Flex. I am sure there are open-source or freeware source for such older systems you could study (unfortunately they are probably all written in assembler, targetting a particular CPU, bus, disk subsystem(s), etc).

One that is fairly "detailed", used by many enthusiasts still today, though, is OS-9 for the Motorola 6809 8-bit cpu (TRS-80 Color Computer); the open-source project NitrOS-9 can be found here:

This is essentially the "modern" version of OS-9 for the Color Computer.

There are probably other resources, too, for "minimalist" 8-bit operating systems. I also know that others here on this forum have created something akin to an OS for the Arduino (some more complex than others) - so this kind of thing is possible to an extent. There are benefits and downsides to using such a system, of course - the biggest one being speed. But you could potentially gain real-time control over the i/o pins and other functionality of the Arduino, plus (if you have a scripting language included - unless there is a way to segment the program flash RAM?) you could have multiple "programs/processes" running at one time (not true multitasking, but something close - more similar to Windows 3.1 than anything).

Ultimately, though, at least on the 168/328 - it would be nothing more than a curiosity and/or learning experience to attempt such an exercise. It reminds me in a great way of when people were hacking QBASIC/QuickBasic to create GUI "operating systems" for DOS, back in the late 1990s. A lot of interesting things came out of that experimentation; maybe the same would be possible for the Arduino.

Perhaps this is one area where a "multi-cpu" Arduino (using SPI or I2C - or even a dedicated parallel bus using the digital i/o lines) could be used as well...?

4919  Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: linux on arduino? on: May 20, 2010, 11:54:22 am
Somehow I doubt it...

IIRC, back in the day (1980s) you could run Microware's OS-9 (multi-tasking, multi-user) on a TRS-80 Color Computer 2 (8-bit 6809), I just don't remember if it required 64k, or if you could get away with 32k...

Of course, this system did require at least one floppy drive (180k, IIRC), and 2 or more drives were recommended (otherwise you were swapping floppies all day long).

Furthermore, this was on a standard (Von Neumann/Princeton) architecture machine, not a Harvard architecture device, like the ATMega is...

4920  Forum 2005-2010 (read only) / Frequently-Asked Questions / Potential -Awesome- Robot Platform? on: May 20, 2010, 12:36:36 pm
I am a little biased on this one; I own one I picked up a Goodwill sans controller...I have yet to do anything with it, but it seems a capable beast!

Check it out - the MGA Tarantula (linking to an ebay auction with them for sale):

I can't vouch for the seller.

Here are a couple of papers detailing interfacing (and a LIDAR system for terrain mapping/planning):

Once again, I am not affiliated with any of these people; I don't stand to make any money off the auction or whatnot - it was just a source (if I had the money and a place to put them - they are HUGE for an RC car - covering about a 24 inch diameter circle - I would buy all six in a heartbeat).

Like I said, I found one of these - and I just happened upon those papers during some googling on "low cost LIDAR"...


[edit]Hmm - I just realized this may have worked better in bar/sport - mods, if you can move it there it would probably be better since this isn't a question, per se.[/edit]
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