I've successfully fixed the DFR-007 backlight cct error using a 1N5819 Schottky diode (a 1N5817 or 1N5818 even better) inserted between the base of Q1 and the pin 10 post (diode cathode to pin 10). The trick was to note the PCB track between these two points is situated on the top surface of the board running out from under the LCD board, through the gap between the J1 and J2 connector strips (referenced to the DFR-007 cct http://www.robotshop.com/content/PDF/dfrobot-lcd-keypad-shield-schematic.pdf and towards the outside edge around to the pin 10 post.
See the attached photos for further guidance.
Code to test with:
//Sample using LiquidCrystal library
#include <LiquidCrystal.h>
/*******************************************************
This program will test the LCD panel and the buttons of
the DFRobot LCD Keypad Shield for Arduino
Product code : RB-Dfr-07
http://www.robotshop.com/dfrobot-lcd-keypad-shield-arduino-1.html
Note cct error identified by Arduino forum discussion at:
http://arduino.cc/forum/index.php/topic,96747.0.html
which advises insertion of a Germanium 1n34a or a Schotky 1N5819
diode between pin 10 and the base of Q1 (K to pin 10).
sample code originally by Mark Bramwell, July 2010
modifications by Dion Weston, March 2012
********************************************************/
// select the pins used on the LCD panel
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
// define some values used by the panel and buttons
int backLight = 10; // LCD Panel Backlight LED connected to digital pin 10
int lightLevel = 255; // Initialise light full on
int lcd_key = 0;
int adc_key_in = 0;
#define btnRIGHT 0
#define btnUP 1
#define btnDOWN 2
#define btnLEFT 3
#define btnSELECT 4
#define btnNONE 5
// read the buttons
int read_LCD_buttons()
{
adc_key_in = analogRead(0); // read the value from the sensor
// my [Mark Bramwell's] buttons when read are centered at these valies: 0, 144, 329, 504, 741
// we add approx 50 to those values and check to see if we are close
if (adc_key_in > 1000) return btnNONE; // We make this the 1st option for speed reasons since it will be the most likely result
if (adc_key_in < 50) return btnRIGHT;
if (adc_key_in < 195) return btnUP;
if (adc_key_in < 380) return btnDOWN;
if (adc_key_in < 555) return btnLEFT;
if (adc_key_in < 790) return btnSELECT;
return btnNONE; // when all others fail, return this...
}
void setup()
{
lcd.begin(16, 2); // start the LCD library
lcd.setCursor(0,0); // move cursor to beginning of line "0"
lcd.print("Backlight adjust"); // print a simple message
}
void loop()
{
analogWrite(backLight, lightLevel);
lcd.setCursor(13,1); // move to position 13 on the second line
lcd.print(lightLevel);
lcd.setCursor(0,1); // move to the begining of the second line
lcd_key = read_LCD_buttons(); // read the buttons
switch (lcd_key) // depending on which button was pushed, we perform an action
{
case btnRIGHT:
{
lcd.print("LED On ");
lightLevel = 255;
break;
}
case btnLEFT:
{
lcd.print("LED Off ");
lightLevel = 1;
break;
}
case btnUP:
{
lcd.print("LED Fade Up ");
if (lightLevel < 255) lightLevel += 1;
break;
}
case btnDOWN:
{
lcd.print("LED Fade Down ");
if (lightLevel > 1) lightLevel -= 1;
break;
}
case btnSELECT:
{
lcd.print("Select ");
break;
}
case btnNONE:
{
lcd.print(" ");
break;
}
}
}
