LCD

The LCD keypad shield looks pretty cool. I like the blue LCD. It is extremely easy to mount the shield onto the arduino. The pin assignment has been taken care of in the example code. However, there is a problem. The unused pins will be totally useless as there will be no easy way to connect them. This is unacceptable. Then, I'm forced to use the old school--manually connect the pins. Luckily, the LCD board on the shield has provided separately its input pins.

Arduino's liquidcrystal library can use minimum of 6 pins to control the LCD:

LiquidCrystal(rs, enable, d4, d5, d6, d7) 

Though there are other pin designation methods, I decide to use the one require least pin numbers for obvious reasons.

Rx need to be tied to GND to enable write. However, it seems to work without grounding it.

I found a website describing the functions of the input pins on the LCD
http://www.8052.com/tutlcd

Here is an example code to print the analog input readings:


#include <LiquidCrystal.h>

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

int adc_key_in  = 0;

void setup()
{
 lcd.begin(16, 2);              // start the library this is a 2 line LCD with 16 characters in each line
 lcd.setCursor(0,0);
 lcd.print("Analog Input"); // print a simple message

}

void loop()
{
 lcd.setCursor(0,1); // move cursor to second line "1" and 9 spaces over
 adc_key_in = analogRead(0);
 lcd.print(adc_key_in);
}

There is a bug that the 4th digit of the analog value does not get refreshed. I will figure something out in the future.

The simplest way turns out to be add a lcd.print("                "); line in the loop. There are probably more decent ways like compare the value with old, if it is different then do a refresh and print the new one. Anyway, it's not very important.

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12/9/2012 update

Regarding the shadow problem of the LCD, it turns out to be more complicated. I discovered another 'working' method:


 lcd.print(distance);
 lcd.print("                ");
 lcd.print(distance);

print the thing you want to print twice with a empty string between them. At least it works for my ultrasonic range finder code.