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4981  Forum 2005-2010 (read only) / Development / Re: Picking a ferrite bead for ENC28J60 on: March 24, 2010, 11:22:34 am
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I'm working on an Arduino clone that will have an embedded Ethernet interface. I'm basing it on the ENC28J60 chip
Me too, sort of.  I don't like not having a modifiable TCP/IP stack.  In a sense the Wiznet is the ultimate in "closed source."  But the amount of code inside the Wiznet is probably larger than will even FIT in an Arduino, so the tradeoffs are interesting...

Have you thought about ENC28J60--AVR--AVR (two avrs), with the first running some network code, and the second running the user's sketch?  (essentially, make a user-programmable equiv of the Wiznet using ENC and an extra AVR.)  In theory, an added advantage could be upload-over-ethernet via a 2nd IP address or special port, connected to the Arduino-AVR serial port...
4982  Forum 2005-2010 (read only) / Development / Re: Setting in resin on: March 19, 2010, 06:48:51 pm
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You want to use a resin that's made FOR display.  Resins made as glue or for surfboards, etc will yellow with age
Resins not specifically made to be clear are likely to start off with some color, as well as a surface that is neither hard nor glossy (This is a "feature", since it helps the next layer stick better.)  Many epoxies are rather brownish, for example.

If you have a TAP Plastics store near you, they'll typically have several different resins for sale, and the stores will have SAMPLES of what the cured resins look like.
4983  Forum 2005-2010 (read only) / Development / Re: opto isotators on: February 26, 2010, 08:12:05 pm
I dunno.  You seem to be using "optoisolator"  interchangeably with "solid state relay."  The usual opto-isolator has a relatively low-power transistor on its output side, so connecting it to control arbitrary loads is relatively complex.  Solid state relays have their own sets of issues (many are good only for AC, for example.)
Optoisolators are also slow, large, not bi-directional, not tri-state, and expensive by arduino standards, and frequently not relevant to the sorts of projects people use Arduino for.  I spent a bit of time once looking for a simple circuit or chip to upgrade the current output of an Arduino (or other microcontroller) pin to 200mA or so, without losing the other features of the Arduino pins.  I didn't find anything, and I wasn't even looking for isolation.  Try to make things bulletproof and very general, and you rapidly arrive at your $600 sorts of solution :-(

There was this opto-isolated H-bridge posted recently:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1265418204
4984  Forum 2005-2010 (read only) / Development / Re: opto isotators on: February 26, 2010, 01:50:58 pm
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Great product but it still cant handle the current needed to power the kind of steppers
I thought you were talking about isolation?  Motor drivers are an entirely separate issue (and one with many more variables, as you note)!  If you're asking for a list/matrix of opto-isolated motor drivers that are compatible with arduino, that's yet a third question...
4985  Forum 2005-2010 (read only) / Development / Re: Crystal used in Duemilanove (Datasheet) on: March 09, 2010, 04:48:10 pm
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You can not get a +/- 100ppm crystal to +/- 10ppm by means of selection.
You could replace the crystal with a +/-10ppm one; they seem to be available...  though it's still probably a silly idea to try to synchronize multiple systems by trying to make sure they all run at the same clock rate...
4986  Forum 2005-2010 (read only) / Development / Re: Crystal used in Duemilanove (Datasheet) on: March 05, 2010, 06:49:27 pm
Good question.  I don't have a lot of faith that the caps associated with the arduino are properly sized; there's a sort of "standard" to plunk down a crystal with a couple of 18 or 22 pF caps, but apparently if you want to do it RIGHT, it's a bit more complicated than that (and you'd need the crystal data sheet to start with.)  OTOH, I've never much cared about higher accuracy than needed to make serial com work, so I haven't been overly motivated to track anything down...

In general, if you want to synchronize multiple CPUs, you have to come up with a solution other than giving them all infinitely-accurate oscillators.

4987  Forum 2005-2010 (read only) / Development / Re: Seriously what is Atmel's problem??? on: March 11, 2010, 11:46:13 am
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What's the difference between the two? What does the A in PA stand for?
Don't know.  "A" is a frequent "sequence number" sort of thing tacked on to a chip number when minor changes are made due to (for example) a new, smaller, chip geometry and size.  Some of the Microchip pics are up to "C", I think.  Frequently there are supposed to not be any customer-visible changes.  OTOH, sometimes there are.  I haven't looked carefully at what Atmel claims...
4988  Forum 2005-2010 (read only) / Development / Re: Seriously what is Atmel's problem??? on: March 11, 2010, 05:40:07 am
The 168 is apparently being phased out and replaced by the 168PA; I suspect the transition is messing with things.  Mouser has some of those:
 http://www.mouser.com/ProductDetail/Atmel/ATMEGA168PA-MU/?qs=sGAEpiMZZMvu0Nwh4cA1wdLkbYSnKaVLTXuBDUZ03ng%3d
4989  Forum 2005-2010 (read only) / Development / Re: power regulator for Xbee? on: March 10, 2010, 06:11:05 pm
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its max output current is 444mA. Do you think it will be enough
"444mA"?!  that's a lot of significant digits for a power supply!  In any case, it sounds OK.  The Arduino itself is well under 100mA, and the max232 is "small" (~10mA, probably depending on loading of the signal lines.)  So it sounds pretty much "just right."
4990  Forum 2005-2010 (read only) / Development / Re: power regulator for Xbee? on: March 10, 2010, 05:22:30 am
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I have read everywhere that I need a power regulator to supply the Xbee chip with 3.3Volts... But why can´t I simply use the Arduino 3.3V pin?
Unfortunately, typical current consumption of the Xbee modules is over 200mA when transmitting, an the Arduino 3.3V pin only provides about 50mA.

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I have already seen several datasheets and I noticed that I normally need a number of capacitors around the power regulator... I am quite a newbie in electronics and I never liked working with capacitors, can I just assume that the circuit that manufacturers provide will work with my Xbee
Yes.  Your requirements are pretty simple.  It should accept 5V as an input (or 6-20V on Vin?) and output 3.3V at up to 400mA or so (to be safe.)  A lot of people are using (and apparently happy with) the LD1117 type regulators here.
4991  Forum 2005-2010 (read only) / Development / Re: External programmer + ATMEGA8-16PU on: February 27, 2010, 09:27:24 pm
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Locally, I can find this chip: ATMEGA8-16PU

a) Can I use my sketch, and compile it in the ide and then use a programmer to get the .hex file into the chip?
The Arduino environment does support the ATmega8, but there are a couple of differences that you might need to be aware of:
1) The mega8 has less memory than the 168 or 328.  A max of 8k of flash memory and 1k of RAM (same as 168 but 1/2 of the 328.)  Some of the applications that people are writing now simply do not fit in a Mega8.
2) Three less PWM outputs.  You only have PWM on pins 9, 10, 11.  in general, the mega8 has "different" timers than 168 or 328.
3) I don't know whether the people writing libraries are still paying attention to mega8; assorted libraries might not work on it (In particular, the ones that use the timers...)
4992  Forum 2005-2010 (read only) / Development / Re: Stand-in capacitor to work with 16MHz crystal? on: March 10, 2010, 12:46:02 pm
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.22uF is one million times larger then the desired 22pf.
Only 10000 times larger.  0.22E-6/22E-12
:-)
4993  Forum 2005-2010 (read only) / Development / Re: PCB etching setup suggestions on: March 06, 2010, 05:55:43 pm
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I would a moderate sized laser etching system.  Then you put your board in and have the laser take off a thin line of copper around the outside of the traces and contacts.  
It's very difficult to remove copper with a laser, though some people have had success removing RESIST with a laser...  $10k is a large amount compared to most hobbyist setups, and not enough compared to most professional setups.  You might look at the yahoo homebrew-pcb group, and http://www.thinktink.com, both of which include the range of professionalism you seem to be after...

4994  Forum 2005-2010 (read only) / Development / Re: More cost effective than Pro Mini for product run? on: March 01, 2010, 12:58:59 am
Well, an ATmega8 remains arduino compatiblity and costs about $3.  It may not be worthwhile searching too hard for an unfamiliar CPU...

4995  Forum 2005-2010 (read only) / Development / Re: Automotive grade arduino? on: February 20, 2010, 01:52:16 am
Well, the atmega324 is a 40-pin chip, rather than the 28-pin chip used in Arduino...
((oops.  I (now) see that you knew this already)
Other than that, it looks like a smaller-memory (32k flash) version of the ATmega644 chip used in "Sanguino", which means it should be pretty easy to put the arduino code on.

BTW, I posted the following off in another thread; I guess it should be repeated here:

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(I don't know what people are looking at at digikey; I can't see and "eol" notices for any 328 varieties...)

The ATmega328 is not so much end-of-lifed as replaced by the nearly identical ATmega328P.  I think that the current generation of Arduinos has ALWAYS used the ATmega328P variety; it's just that the differences haven't been particularly relevant to the audience.  Certain particularly paranoid microcontroller customers will have to do another round of "qualification" testing of the chip within the context of their product to make sure that it REALLY hasn't changed in any significant way, but Arduino is not likely among these.

The Atmel site says that ATmega8, ATmega168, and ATmega168P, are ALL "not recommended for new designs."  They're replaced by ATmega8A and ATmega168PA respectively...
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