JHD204A LCD problem

[KP_OZ]

I have bought a JHD204A LCD (20 x 4) display, but cannot get the contrast to work .
I have wired pins 1 and 16 to -ve (ground), and pins 2 and 15 to 5Volts +ve - as specified in the data sheet.
Pin 5 (the Read/Write select) is connected to ground (-ve).
Pin 3 (Vee) is used to adjust the contrast - and is connected to the wiper of a 10K potentiometer (variable resistor - called a pot ). The other wires of the potentiometer are connected to -ve (earth) and 5V +ve.
I have measured the voltage on pin3, and by turning the pot the voltage is varied between 0 and 5v.

When the power is applied to the JHD204A, the backlight turns on, and rows 1 and 3 show bright pink/purple rectangles.
Turning the potentiometer has no effect on the display.
I have 2 different LCD displays that work correctly using this set-up, and the contrast can be adjusted on these LCDs.

As a further check, I connected the data lines of the JHD204A to my Arduino, and used the example code of "Hello World".
The only change I made to the code, was to alter the lcd.begin(16,2) to lcd.begin(20,4) - since the JHD204A is a 20 x 4 display.
No characters show on the JHD204A. The LCD remains the same as before when only power was connected.

I have 2 other models of LCD display that work correctly - using the same setup as above.
Is there some manufacturer change in the specifications or pins of the JHD204A, or a fault with the design of the JHD204A ?
I have searched the internet, and noticed other forum posts with the same problem using the JHD204A (eg contrast does not work).
Without the ability to change contrast, the LCD cannot be used as a display.
Any assistance greatly appreciated......................KP_OZ

[techsupport]

Hi friend;
Turning the pot doesn't affect the contrast, it is supposed to be the fault of the design.But the data displayed is clearly visible.
Do you follow the wiring diagram below?
http://www.geeetech.com/wiki/index.php/1602_LCD

[KP_OZ]

As per my post, all wiring is correct as per the data sheet........KP_OZ

[albdiag]

i have the same problem

[KP_OZ]

Hi Albdiag - it seems to me the manufacturer has made a change to the design, and the JHD204A does not have a contrast function.

Despite days of effort, I could not get contrast to work, however the The LCD will display the data at full brightness.
My JHD204 only showed pink/purple squares until it was initialised by the code on the Arduino.
As you probably know, the code must include 3 things :
The library : #include <LiquidCrystal.h>
The initialise command : LiquidCrystal lcd(7,8,9,11,12,13);
and in void setup() : lcd.begin(20,4); // where the integers are the number of characters and rows.
With the above code in place, this command works - lcd.print("hello, world!");

I wired it as follows :
Pin 1 connected to pin 16 and connected to earth;
Pin 2 connected to pin 15, and connected to 5v +ve.
Pin 5 connected to earth.
Pins 4,6, 11,12,13,14 can be connected to any 6 pins of the Arduino, make certain you use the Arduino pin numbers in the initialise statement.
For example, connect the LCD pins 4,6,11,12,13,14 to the Arduino pins 7,8,9,11,12,13 and initialise with : LiquidCrystal lcd(7,8,9,11,12,13);
Any six pins of the Arduino can be used, but the initialise command must be in the order of RS ( LCD pin4); Enable (LCD pin 6) ; LCD pins D4;D5;D6;D7
IsecSV kindly offered to replace my unit, however the display does work at full brightness, so I declined.
Hope you succeed with your display......................Keith

[techsupport]

Hi Friends,
We upload a new 2004 demo file.zip at: http://www.geeetech.com/lcd2004-white-w ... p-124.html
Please refer to this file, you can solve your problem with this reference,
Thanks,
Regards