[am not]

I know that people have used the Arduino and a cellular shield (such as https://www.sparkfun.com/products/9607) to send text messages. Would an Arduino be capable of actually making voice calls over a shield?

I've never had a GSM shield myself, so I don't know how much would be done directly on the cellular module or on the Arduino's CPU. Would making voice calls over an Arduino be a feasible project?

Please note that I am not trying to create a device comparable to a commercial cellphone. I saw that someone else created a similar topic a while back (http://arduino.cc/forum/index.php/topic,55455.15.html) about building a commercial cell phone using an Arduino. My cell phone would not be a commercial product; it would merely be a novelty for my own personal use, and portability would not be a design goal. (If the device was the size of a lunchbox and didn't even have batteries, I wouldn't care)

Could I do this or is it impossible to use an Arduino as a telephone? If possible, could someone point me in the right direction to get started?

I have a book of Arduino projects, and one calls for the LM35DT (http://www.national.com/mpf/LM/LM35.html#Overview) analogue temperature sensor. However, it says you can use any other analogue temperature sensor. Will the LM335A (http://www.sparkfun.com/products/9438) work directly in its place, or does it have different requirements?

I soldered everything again, and it worked!  Thanks for the support. Now I won't waste my money on a new LCD.

It's probably OK.  Did you follow this step?

Next we'll connect up the backlight for the LCD. Connect pin 16 to ground and pin 15 to +5V through a series resistor. To calculate the value of the series resistor, look up the maximum backlight current and the typical backlight voltage drop from the data sheet. Subtract the voltage drop from 5 volts, then divide by the maximum current, then round up to the next standard resistor value. For example, if the backlight voltage drop is 3.5v typical and the rated current is 16mA, then the resistor should be (5 - 3.5)/0.016 = 93.75 ohms, or 100 ohms when rounded up to a standard value. If you can't find the data sheet, then it should be safe to use a 220 ohm resistor, although a value this high may make the backlight rather dim.

Yes, I did follow that step (using a 220 ohm resistor). The backlight has always worked fine, but the screen output is always the same as in the image I had in my original post.

My problem ended up being my poor soldering of the pin headers, and so I redid it and fixed it.

I'll try that today. This was my first time working with pin headers, and my soldering wasn't all that great (although I thought it was good enough).

Did you do this step:

Open up the File→Examples→LiquidCrystal→HelloWorld example sketch

Now we'll need to update the pins. Look for this line:

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
And change it to:

LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
To match the pin table we just made.

Now you can compile and upload the sketch

Yes, I did this already. I followed all the instructions perfectly. I also tried some other similar tutorials previously to no avail.

Unless anyone else has any more ideas, I'm fairly certain now that the display is broken. I'm considering buying this one to replace it: http://www.adafruit.com/products/181. Does anyone know from personal experience if this is a good deal?

So I followed the excellent tutorial at http://www.ladyada.net/learn/lcd/charlcd.html and got the contrast circuit for my 16x2 display working. But after completing the tutorial, no text appeared on my screen. No matter how many times I check my wiring, the display looks like this image from the tutorial: (Please note that unlike the image all of my bus wiring is complete.)

So I'm wondering now if this display is broken. Is there something I missed, or must I buy a new LCD?

I'm modifying a kid's robot toy with the Arduino. There is a photoresistor that, when light touches it or when I connect its two leads together, causes the robot to move backwards. I would like the Arduino to force the robot on occasion to move backwards, by making a temporary connection each time between the two leads of the photoresistor. I could, I suppose, use a relay, but I don't happen to have any and would like a more elegant solution. Any ideas?

So I got this LED dot-matrix display from Sparkfun (http://www.sparkfun.com/products/681) only I'm not sure which pins correspond to which LEDs. Tried the datasheet on Sparkfun's site but it doesn't say which pins are which. I'm too lazy to manually find out which pins do what , so if anyone knows if there is already a diagram for these things somewhere online that would save me some time that would help. If not, I'll just figure it out myself.

Thanks so much for the replies. I'll try the suggesstions as soon as I get some free time.

[setup]

I'm trying to connect a character display I just bought from http://www.gadgettown.com/LCD-Module-White-Characters-Blue-Backlight-HD44780.html to an Arduino Uno, using the instructions from my Beginning Arduino book. Unfortunately, the screen's backlight comes on, but the LCD remains blank. Any idea what's wrong?

Code:

// PROJECT 23
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2); // create an lcd object and assign the pins

void setup() {
     lcd.begin(16, 2); // Set the display to 16 columns and 2 rows
}

void loop() {
     // run the 7 demo routines
     basicPrintDemo();
     displayOnOffDemo();
     setCursorDemo();
     scrollLeftDemo();
     scrollRightDemo();
     cursorDemo();
     createGlyphDemo();
}

void basicPrintDemo() {
       lcd.clear(); // Clear the display
       lcd.print("Basic Print"); // print some text
       delay(2000);
}

void displayOnOffDemo() {
     lcd.clear(); // Clear the display 
     lcd.print("Display On/Off"); // print some text
     for(int x=0; x < 3; x++) { // loop 3 times
          lcd.noDisplay(); // turn display off
          delay(1000);
          lcd.display(); // turn it back on again
          delay(1000);
    }
}

void setCursorDemo() {
     lcd.clear(); // Clear the display
     lcd.print("SetCursor Demo"); // print some text
     delay(1000);
     lcd.clear(); // Clear the display
     lcd.setCursor(5,0); // cursor at column 5 row 0
     lcd.print("5,0");
     delay(2000);
     lcd.setCursor(10,1); // cursor at column 10 row 1
     lcd.print("10,1");
     delay(2000);
     lcd.setCursor(3,1); // cursor at column 3 row 1
     lcd.print("3,1");
     delay(2000);
}

void scrollLeftDemo() {
     lcd.clear(); // Clear the display
     lcd.print("Scroll Left Demo");
     delay(1000);
     lcd.clear(); // Clear the display
     lcd.setCursor(7,0);
     lcd.print("Beginning"); 
     lcd.setCursor(9,1);
     lcd.print("Arduino");
     delay(1000);
     for(int x=0; x<16; x++) {
          lcd.scrollDisplayLeft(); // scroll display left 16 times
          delay(250);
     }
}

void scrollRightDemo() {
     lcd.clear(); // Clear the display
     lcd.print("Scroll Right");
     lcd.setCursor(0,1);
     lcd.print("Demo");
     delay(1000);
     lcd.clear(); // Clear the display
     lcd.print("Beginning"); 
     lcd.setCursor(0,1);
     lcd.print("Arduino");
     delay(1000);
     for(int x=0; x<16; x++) {
       lcd.scrollDisplayRight(); // scroll display right 16 times
          delay(250);
     }
}

void cursorDemo() {
     lcd.clear(); // Clear the display
     lcd.cursor(); // Enable cursor visible
     lcd.print("Cursor On");
     delay(3000);
     lcd.clear(); // Clear the display
     lcd.noCursor(); // cursor invisible
     lcd.print("Cursor Off");
     delay(3000);
     lcd.clear(); // Clear the display
   lcd.cursor(); // cursor visible
     lcd.blink(); // cursor blinking
     lcd.print("Cursor Blink On");
   delay(3000);
     lcd.noCursor(); // cursor invisible
     lcd.noBlink(); // blink off
}


void createGlyphDemo() {
     lcd.clear();

     byte happy[8] = { // create byte array with happy face
     B00000,
     B00000,
     B10001,
     B00000,
     B10001,
     B01110,
     B00000,
     B00000};
  
     byte sad[8] = { // create byte array with sad face
     B00000,
     B00000,
     B10001,
     B00000,
     B01110,
     B10001,
     B00000,
     B00000};
     lcd.createChar(0, happy); // create custom character 0
     lcd.createChar(1, sad); // create custom character 1
 
    for(int x=0; x<5; x++) { // loop animation 5 times
         lcd.setCursor(8,0);
          lcd.write(0); // write custom char 0
          delay(1000);
          lcd.setCursor(8,0);
          lcd.write(1); // write custom char 1
          delay(1000);
     }
}

Here's what it should look like when set up:
https://picasaweb.google.com/lh/photo/WzOfEcDjvq2yOXSSItNe9Q?feat=directlink

And this is what I have:
https://picasaweb.google.com/lh/photo/OFMoxPPRcWy1m8TrkahhTQ?feat=directlink

Is the LCD broken or am I doing something wrong?