problem with Sparkfun serial backlit 16x2 LCD

Other Hardware Displays
1

I have been trying to read the voltage value of the analog pin and print it to my lcd but it just prints a bunch of weird characters. any help would be great. here is my sketch. I am new to programming so I wouldn't be surprised if I was dead wrong on what I have already done. BTW the lcd works when I tell it to write regular phrases.

#include <SoftwareSerial.h>


SoftwareSerial mySerial(3,2); 
String string=String(analogRead(0), DEC);
void setup()
{
  mySerial.begin(9600); // set up serial port for 9600 baud
  delay(500); // wait for display to boot up
}

void loop()
{
  mySerial.write(254); // move cursor to beginning of first line
  mySerial.write(128);
  mySerial.println(string);//prints the value of the initialized String (I hope)
  delay(2000);

  mySerial.write("                             "); // clear display
  mySerial.write("                             ");

  mySerial.write(254); // move cursor to beginning of first line
  mySerial.write(128);

  delay(2000);
}
2

I think one problem is that you're using "println" instead of "print". println sends a carriage return and a line feed that might be the last two strange characters you see. That doesn't explain why you don't see the results of the analog read.

I don't see why you position the cursor both before and after the printing of the data.

On the other hand, if you position the cursor before you print your spaces, that will erase the old data but you still need to look into the LCD addressing. From your code I'm guessing that you think you're erasing both lines on the LCD by sending out two lines of spaces. The LCD addresses for the two lines aren't consecutive.

3

ok thanks for replying. I changed the println command into a print command and it got rid of the strange characters but it prints nothing but zero no matter how much (safe) voltage I send through it. Am I forgetting to initialize something? any help would be awesome. I kept the spaces in just for the heck of it.
my revised code

#include <SoftwareSerial.h>

SoftwareSerial mySerial(3,2); 
String string=String(analogRead(A0));
void setup()
{
  mySerial.begin(9600); // set up serial port for 9600 baud
  delay(500); // wait for display to boot up
}

void loop()
{
  mySerial.write(254); // move cursor to beginning of first line
  mySerial.write(128);
  mySerial.print(string);
  delay(1000);

  mySerial.write("                             "); // clear display
  delay(1000);//also lowered the timing for quicker refresh times
}
4

I'm not sure what you're trying to accomplish. If it's periodic readings of the analog pin, you should be reading it in the loop() and not in setup().

I think you need to reposition the cursor before executing
mySerial.write(" "); // clear display

I don't understand why you've got the delay after you print the spaces. Do you want to have the screen blanked for 1 second after each reading?

5

you've been a great help. I put the read into the loop and now the voltage changes! and it prints it to the LCD but is there any way to convert that number which is from 300 to 1000 into a real voltage? and also the voltage changes erratically. is there a way to get an accurate reading of the voltage i am inputting? btw i'm trying to build an arduino ohm meter

#include <SoftwareSerial.h>

SoftwareSerial mySerial(3,2); 
void setup()
{
  mySerial.begin(9600); // set up serial port for 9600 baud
  delay(500); // wait for display to boot up
}

void loop()
{
  String string=String(analogRead(A0));
  mySerial.write(254); // move cursor to beginning of first line
  mySerial.write(128);
  mySerial.print(string);
  mySerial.print(" Volts");//I added this as a label
  delay(1000);
  mySerial.write(254); // move cursor to beginning of first line
  mySerial.write(128);
  mySerial.write("                             "); // clear display
}
6

There are several ways to convert from the analog read values to another set of units. Read about the map function, it's pretty slick.

If your goal is an ohmmeter, why to you want to read "real voltage"?

For the erratic readings, this tutorial on smoothing should be interesting to you.

7

Iam going to use a resistor and hook it up to an analog pin then have probes going to the unknown resistance which goes into another analog pin. then I will split the voltage through the resistor and the unknown resistance. then its a simple equation to derive the resistance of the unknown resistance. the constantly fluctuating voltage will throw off my reading.

8

arloG:
map() - Arduino Reference
...
http://arduino.cc/en/Tutorial/Smoothing#.UxQDW_iP5XQ

It is neater to remove the tracking garbage from the end of your quoted URLs.

It is even neater :smiley: to just insert the hyperlinks into your description using the "Insert Hyperlink" button with the little world icon. You put an equals sign after the "url" before the "]" and paste the actual URL after that.

kklee97:
The constantly fluctuating voltage will throw off my reading.

You might want to use a capacitor on the Vref pin. Just how much does the voltage/ reading fluctuate?

9

It is neater to remove the tracking garbage from the end of your quoted URLs.

It is even neater smiley-grin to just insert the hyperlinks into your description using the "Insert Hyperlink" button with the little world icon. You put an equals sign after the "url" before the "]" and paste the actual URL after that.

Thanks for pointing this out. I was oblivious.