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391  Using Arduino / LEDs and Multiplexing / Re: big multiplexing tri colour led cube - will it refresh fast enough ? on: January 16, 2012, 08:40:54 pm
Resistor value depends on the LED, voltage, and current. You can use this page to calculate:

http://ledz.com/?p=zz.led.resistor.calculator

One thing to note is that if you're absolutely certain your pulses will be fast enough (typically 0.1 MS or faster) you can overdrive many LEDs. For example a bunch of SMD LEDs I used in a recent project normally run at 20 mA but for short pulses can be driven up to 120 mA. The upshot is they're almost (but not quite) as bright when being strobed in a matrix as they would be when run standalone.

Chris
392  Using Arduino / Project Guidance / Re: 4MB of RAM? on: January 16, 2012, 12:21:02 pm
Sure. One option would be to run the 3 IO pins out to a demultiplexer like a 74ahc138, have those outputs control / select 8 different banks of 512K RAM, then use the rest of the author's plans.
393  Using Arduino / Project Guidance / Re: 4MB of RAM? on: January 16, 2012, 12:00:28 pm
Per Grumpy Mike's suggestion, here's an example of somebody doing what you want:

http://www.radiolocman.com/shem/schematics.html?di=109611

Good luck!
394  Using Arduino / LEDs and Multiplexing / Re: big multiplexing tri colour led cube - will it refresh fast enough ? on: January 16, 2012, 11:30:12 am
Even if you go with a mega I think RAM will be a problem. 24x24x24 x 2 LEDs will need 27K of memory at 8 bit resolution; you'll need even more to go to 12 bit.

As Grumpy Mike says I also think you'll have to drive multiple planes at a time. 24 planes x 256 slots of PWM x 50 Hz (so the eye won't see the redraws) is about 300 000 updates per second. That only gives a 16 MHz processor about 52 clock cycles to get ready to update the next row, which I don't think is possible.

Good luck!
395  Using Arduino / Microcontrollers / Re: Arduinos- why 16MHZ instead of 20? on: January 14, 2012, 01:51:38 am
It's for historical compatibility - the first chip the arduino used was 16 MHz and that's where it's stayed.

See

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1218758665

for more details.
396  Using Arduino / Networking, Protocols, and Devices / Re: Wireless control of an Arduino via iphone on: January 13, 2012, 10:54:08 pm
Lots of questions, unfortunately no answers on the wifi shield, the Leonardo, the Due....
397  Using Arduino / Networking, Protocols, and Devices / Re: Wireless control of an Arduino via iphone on: January 13, 2012, 07:51:08 pm
Well that's really disappointing news on Ciao. I'd hoped to use it in a future project...

I think the biggest problem you're going to have with adhoc WiFi and Arduino is it's going to be dependent to the specific chipset / shield you use, since there's no official Arduino WiFi yet. For example the Sparkfun wifly shield (http://www.sparkfun.com/products/9954) seems to be popular, but it doesn't look like it supports ad hoc (the library says it's on the "to do" list).

On the plus side, if you're using WiFi outdoors you should get pretty good coverage because there won't be anything obstructing the signal.

I saw your post in another thread regarding the availability of the official Arduino WiFi shield...I doubt this is much comfort to you but there's a lot of us in that same boat....

Chris
398  Using Arduino / Networking, Protocols, and Devices / Re: Sending E-mails, and calling NTP server on: January 13, 2012, 05:49:50 pm
The Arduino Time library

http://arduino.cc/playground/Code/Time

includes an example on using NTP.

Email is unfortunately a little more complicated, due to the complexity that various security / spam concerns have added over the years which make SMTP not so "S" any more. The easiest method is probably to find a trusted host that will do the actual email relay for you, connect to it on port 25 with one of the telnet client libraries, and do the basic HELO, MAIL-FROM, etc. commands with prints. Here's an example:

http://arduino.cc/forum/index.php/topic,50541.0.html

Good luck!
399  Using Arduino / Networking, Protocols, and Devices / Re: Wireless control of an Arduino via iphone on: January 13, 2012, 05:39:28 pm
Easily.

Option 1 - write your own web server & use the Bonjour library to connect to it:
http://arduino.cc/en/Tutorial/WebServer
http://gkaindl.com/software/arduino-ethernet/bonjour

Option 2 - Use Ciao to do most of the heavy lifting for you:
http://bildr.org/2011/05/ciao/

Good luck!
400  Using Arduino / General Electronics / Light sensors versus photoresistors on: January 10, 2012, 02:51:47 pm
It looks like a lot of the Arduino tutorials etc. like this:

http://www.ladyada.net/learn/sensors/cds.html

use photoresistors like these:

http://www.futurlec.com/Photocells.shtml

but from what I can tell it doesn't looks like "real" products use them very often, instead they use light sensor ICs like this:

http://search.digikey.com/us/en/products/ALS-PDIC243-3B/1080-1018-ND/2675509

even though they're more expensive, and sometimes more complicated to use. Can anyone tell me why? Are the ICs better at evaluating light than the photoresistors? I've found that photoresistors aren't particularly fast, but for many/most applications (like a TV backlight) speed isn't that important. Is it a RoHS compliance thing?

Thanks as always!
401  Using Arduino / Microcontrollers / Re: A cubical microcontroller based toy on: January 10, 2012, 11:31:21 am
Bug Labs?

http://www.buglabs.net/products
402  Using Arduino / Networking, Protocols, and Devices / Re: How to see Arduino in Windows network (network name) and accessing files on SD? on: January 09, 2012, 11:22:49 pm
Hi MrGlasspoole,

I don't think I can offer much help regarding moving the files from the SD card to your PC, but hopefully can at least point you in the right direction on the network name:

I am looking to do something similar with a project I'm working on right now and don't have a concrete answer yet, but you need to install something that does dynamic / multicast DNS advertisements.

So far it looks like the Bonjour library for Arduino is the best candidate:

http://gkaindl.com/software/arduino-ethernet/bonjour

If this works for you, please let me know.

Good luck!
403  Using Arduino / Project Guidance / Re: How fast can Arduino Uno switch ouput pins? on: January 06, 2012, 10:29:52 pm
Short answer: yes, easily.

Slightly longer answer: 125 IOs / second * 20 = 2500 / second. A standard Arduino runs at 16 Mhz, which means it has 6400 clock cycles to do what you need. Even the (relatively) slow digitalWrite() command takes only about 17 clock cycles, leaving you lots of time to do other stuff.

Good luck!
404  Using Arduino / General Electronics / Re: software for electrical diagrams on: January 03, 2012, 06:09:34 pm
If you mean schematics and boards, a lot of people here use the free / light version of Eagle:

http://www.cadsoftusa.com/downloads/freeware/?language=en

Good luck!
405  Using Arduino / Networking, Protocols, and Devices / Re: Is it possible to use a different pin for MISO? on: December 29, 2011, 10:09:17 pm
I agree with retrolefty on replacing your board, but if you want to try it in software here's some code from someone who's done it:

http://little-scale.blogspot.com/2007/07/spi-by-hand.html

Good luck,

Chris
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