Show Posts
Pages: 1 ... 331 332 [333] 334 335 ... 452
4981  Forum 2005-2010 (read only) / Development / Re: Freeduino Suppliers? on: April 22, 2009, 09:28:40 pm
I think that most of the distributors of the Boards labeled "Freeduino" ARE the manufacturers of the boards as well.  This is certainly true of NKC,  MDC, and SeeedStudio for example (although those are three different "sorts" of Freeduino.  "Freeduino" as name is not controlled at all, so anyone can call anything a freeduino.)

This is part of the motivation for "Freeduino" - by knocking out a level of distribution, you (theoretically, anyway) increase profit margins (or decrease costs) by a significant amount.  I would expect that most of the Freeduino distributors might be open to discussions about buying bare board if you're talking about buying lots at one time.  (some already sell bare boards.)  Or you can take the design files and send them out to a PCB shop and get boards made on your own.  (so far, it looks like contract manufacturing to get complete board rather than bare boards or kits, has not been cost effective.)
4982  Forum 2005-2010 (read only) / Development / Re: Mega 1280 Daughterboard? on: April 28, 2009, 03:44:31 pm
- should be fairly cheap, the chip seems to be $10 or less
The problem is that by the time start with the $10 chip, design a PCB board, add pins to plug into the existing socket, and have the whole thing assembled, figure in the markups  at least one level of distribution, you're looking at a pretty expensive proposition...

The 328 is a painless upgrade.  I don't think the mega1280 would be (and ... how do you wire the conflicting pins like SPI?  Arduino compatible?  Or MEGA subset compatible?   Issues, issues...)
4983  Forum 2005-2010 (read only) / Development / Re: Whats wrong with my device? on: April 15, 2009, 03:56:05 pm
I checked the current, and with the dial at 200m it read 108.5.
That should be fine overall.  Let us know if the bad connection fix doesn't seem to fix it afterall...
4984  Forum 2005-2010 (read only) / Development / Re: Whats wrong with my device? on: April 14, 2009, 03:37:20 pm
The current and voltage are intimately related (V=I*R), and the current everywhere in a series circuit is the same, so it sounds like you have it wired right, even if your understanding is slightly off (the voltage across the LED will be approximately constant regardless of current, and if the voltage of the supply is greater than the voltage of the LED, in theory LOTS of current will flow, which is why you need the resistor.)  What value of resistor are you using?

While putting an LED directly across a 5V supply will probably burn out the LED, the AVR in the arduino has some internal resistance , and will USUALLY not do so.  But you can get yourself into trouble expecting that to scale to lots of LEDs, or in other circumstances.  You should have resistors, but just because your LEDs haven't burnt out doesn't mean you have the RIGHT resistors.
4985  Forum 2005-2010 (read only) / Development / Re: Whats wrong with my device? on: April 14, 2009, 01:03:21 am
My math says 20ma * 12 = 240ma per hour for the leds.. add a little for the arduino running at 16mhz.  On three AA batteries that should get a few weeks of use right?
Well, no.  A set of AA batteries is probably good for about 2500mAH of power, so they'd run out of juice in a 240mA circuit in about 10 hours.  On the other hand, it still shouldn't flake out after less than one hour.

OTOH, even 240mA is above the limit that is supposed to be allowed for the whole chip (200mA)

You DO have current limiting resistors of some sort in there, don't you?  An LED will happily consume more than it's rated current without a resistor, and doing THAT 12x over could be a problem in several ways.  I would be inclined to use ~100 ohm resistors for each TWO leds (in the side to the power rail), which would preserve your ability to do patterns and such and give you "full brightness" if you happened to only light one of each pair, and reduced overall current if you have both LEDs in a pair turned on.
4986  Forum 2005-2010 (read only) / Development / Re: Capacitor values for external crystal oscilator? on: April 16, 2009, 03:43:15 pm
I suspect that one of the reasons that it is so common to have a crystal circuit where someone has just "thrown on" the "typical value" 18 or 22pF caps, rather than carefully analyzed the PCB with respect to the particular crystal they are using is that initial designs tend to be built based on crystals from "hobbyist" sources where there IS no detailed datasheet for the crystal.

The two 22pF caps from the arduino basic schematic will almost certainly work with any crystal you are likely to find from suppliers similar to the one mentioned in this thread.  If you need "as much accuracy as you can get", you might want to buy a crystal from a supplier that does have a data sheet, and then carefully tune the cap value while watching a highly-calibrated scope and/or frequency counter.   If you have a particularly "weird" capacitor (ultra mini smt, for instance), you might worry about it more...
4987  Forum 2005-2010 (read only) / Development / Re: Capacitor values for external crystal oscilator? on: April 13, 2009, 12:12:05 am
Don's equations are correct, but the 30pF capacitance that you (the OP) quoted is pretty far outside the normal range of such crystals; digikey doesn't list any 16MHz crystals with a load capacitance above 20pF, for instance, and assorted Atmel data sheets and Microchip App notes say that 17pF is "typical."
Almost everyone throws a couple of 18-22pf caps in there and has it work right, despite the fact that you SHOULD take a bit more care...

4988  Forum 2005-2010 (read only) / Development / Re: Good Wire to PCB Option? on: March 25, 2009, 08:18:20 pm
See also: which includes some part numbers...

The big decision is how small your want the connectors.  getting them on 0.1 inch centers is possible, but seems to be pricier than the "normal" size of about twice that.
4989  Forum 2005-2010 (read only) / Development / Re: Shield-Duino on: March 25, 2009, 08:21:06 pm
One problem is that the Arduino form-factor is pretty limited on the amount of space you have at the edges for putting connectors, especially if you're trying not to interfere with the "tall" components on the main Arduino board...
4990  Forum 2005-2010 (read only) / Development / Re: Shield-Duino on: March 24, 2009, 03:59:40 pm
I see no value in all these shields that "bring up" the ICSP headers from the original board
The original (and followon) Zigbee shields use the ICSP header for power (grr.)  Several shields (mostly proto shields?) that pre-date diecimila  use it to extend "RESET" of the arduino to the shield (button, or for bootload-via-shield capability.)  I don't like it either :-(
4991  Forum 2005-2010 (read only) / Development / Re: Shield-Duino on: March 24, 2009, 10:29:24 am
this could be "multi" core, if designed correctly, right?
Yes, assuming SPI or some multi-drop serial protocol.  But mostly it probably equates to an easy way to make a stock arduino into a "dual core" arduino.  

What about having two set of headers?
So that one could stack an additional shield on top of shielduino.
Yes, that's the plan.  The original arduino shield connectors would stack, and the equivalent connections form the "coprocessor" would go somewhere else.  (next to the proto area in the pcb pictured.)  That lets you add additional shields to the original arduino, but doesn't let you add shields to coprocessor.
4992  Forum 2005-2010 (read only) / Development / Re: Shield-Duino on: March 24, 2009, 02:41:37 am
Works fine if your logged into picasaweb as me :-)
Fixed?  maybe?  It's just a rough draft picture anyway...
4993  Forum 2005-2010 (read only) / Development / Shield-Duino on: March 24, 2009, 12:08:17 am
There are a lot of things that the ATmega CPU on an arduino could be programmed to do, relatively easily, that are a bit ... exclusive ... of having the arduino do other (normal) things.  They might have tight timing requirements, use up large amounts of the available CPU time, use timers in ways that conflict with analogWrite(), and so on.  Multiple servo motors, multiple serial ports, and large display (video or LED) refresh are typical examples.  Yet the Arduino environment is known and understood, and it would seem a shame to require a special purpose shield to do the same thing that an arduino could do.

So... What do you think about putting the basic Arduino core (16MHz Atmega168/etc) ON A SHIELD.  Essentially a "slave" arduino, or an arduino "co-processor" based on Arduino...

It would communicate with the main arduino by serial or SPI.  It could be programmed by running a special "relay" sketch on the main arduino, or by ICSP, or by unplugging the 168 and plugging it into a real arduino.  It would tap power from the main board, as per most shields, and replace the power and usb areas of the normal arduino with a prototyping area for additional circuitry.  The PCB could double as a "reduced" arduino "runtime board." Ardunio shield connectors would stack, and new connectors would show up "elsewhere."   Even mere pin expansion would be reasonable; a shield board with an ATmega8 wouldn't be THAT much more expensive to build than a shield board with a couple if 74hc595s, and it would be a LOT more flexible.

What do you think ?

4994  Forum 2005-2010 (read only) / Development / Re: How much RAM is used? on: April 04, 2009, 12:07:29 am
many tiny platforms have a non-enforced sliding barrier between heap and stack
Now that you mention that, I'm not sure.
So since this is coming up more and more frequently, I went and took a look at the initialization code in a compiled sketch.  It does in fact simply initialize the stack pointer to the top of the RAM area, and it is permitted to grow downward (toward the space occupied by malloc'ed data, uninitialized data, and initialized data) with no checking.  Also, malloc() does compare things against the current value of the stack pointer.   So it DOES have exactly the sort of sliding window between heap and stack that Halley describes....
4995  Forum 2005-2010 (read only) / Development / Re: How much RAM is used? on: January 13, 2009, 08:34:25 am
many tiny platforms have a non-enforced sliding barrier between heap and stack

Now that you mention that, I'm not sure.
Pages: 1 ... 331 332 [333] 334 335 ... 452