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1  Community / Products and Services / Re: Power LED Shield V2 on: August 14, 2011, 03:18:42 am
I'm planning a project to modify my floor lamp to use RGB LEDs. I'm using this lamp:
http://www.ikea.com/us/en/catalog/products/80028552

For this project, I'm considering using the Power LED Shield to power one, preferably two of these RGB LED plates:
http://www.dealextreme.com/p/30w-1500-lumen-rgb-led-emitter-metal-plate-39960

The green and blue channel require at least 32V, so it seems I need to find a 32V power supply. Unfortunately, I only need three channels, one for each color, so I'm not sure what to do with the four channel. Maybe I'll use it to power a white LED assembly.

Will I be able to power two of these RGB plates with one shield? If not, can two stacked shield share the same power supply?

For 32V, I think I can't use a laptop DC adapter as those supply only 24V. Any recommendations for those?
2  Using Arduino / Displays / Re: 1602 LiquidCrystal mystery on: August 12, 2011, 09:41:28 pm
Thanks for all the answers. The problem went away after I connected a series resistor to the LED. However, I'm curious to know an explanation of what actually happened, electrically speaking. Does having a high current on one digital pin affect the logical output of another digital pin? Perhaps this is due to too much current going through that pin so that there is not enough left for the other pins for accurate signalling?

Today is my second day experimenting with an Arduino, and I've learned that you actually need to limit the current to an LED as the pins don't have built-in resistors, not only to avoid damaging the components, but also to avoid weird behavior.
3  Using Arduino / Displays / 1602 LiquidCrystal mystery on: August 11, 2011, 11:42:31 pm
Hi guys,

I connected my Uno to a 1602 16x2 LCD. I seem to be able to control it fine using the LiquidCrystal library. However, I decided that I wanted to leave the PWM digital pins free and switched to using a different signal pin assignment instead. I used the wiring in here with some modifications:
http://arduino.cc/en/Tutorial/LiquidCrystal

Modifications:
No pot -- Pin 3 is connected to ground instead of a pot
Pin 15 to +5V and Pin 16 to ground
Pins 2, 4, 7, 8, 12, 13 instead of Pins 2, 3, 4, 5, 11, 12, respectively

I also connect (Digital Pin 3, Ground) to an LED. With the LED connected, the following code produces garbled output on the LCD. If I disconnect the LED, comment out the lines outputting to Digital Pin 3, or output 0 or 255 instead of 127, the output is fine. I would like to understand why this is happening. It seems that outputting to Pin 3 is somehow affecting the other pins that control the LCD. In this case, 'garbled' means the screen is filled with 'S' and '5' characters and constantly flickers on both the top and bottom lines as if being updated.


Code:
#include <LiquidCrystal.h>

LiquidCrystal lcd(13, 12, 8, 7, 4, 2);

#define LED 3

void setup() {
  pinMode(LED, OUTPUT);
  lcd.begin(16, 2);
  lcd.print("Hello, world!");
}

void loop() {
  analogWrite(LED, 127);
  lcd.setCursor(0, 1);
  lcd.print(555);
}
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