Determining contrast on LCD

Question

So I am using this code here and I do get text written on my LCD screen. Problem is that text is almost invisible. I tried with background light on or off and it did not help. LCD is connected to 5v and backlight is connected to 3.3V. Backlight is connected through potentiometer.

How to control text contrast? To have more contrast?

#define PIN_SCE 7
#define PIN_RESET 6
#define PIN_DC 5
#define PIN_SDIN 4
#define PIN_SCLK 3
#define LCD_C LOW
#define LCD_D HIGH
#define LCD_X 84
#define LCD_Y 48
static const byte ASCII[][5] =
{
 {0x00, 0x00, 0x00, 0x00, 0x00} // 20 
,{0x00, 0x00, 0x5f, 0x00, 0x00} // 21 !
,{0x00, 0x07, 0x00, 0x07, 0x00} // 22 "
,{0x14, 0x7f, 0x14, 0x7f, 0x14} // 23 #
,{0x24, 0x2a, 0x7f, 0x2a, 0x12} // 24 $
,{0x23, 0x13, 0x08, 0x64, 0x62} // 25 %
,{0x36, 0x49, 0x55, 0x22, 0x50} // 26 &
,{0x00, 0x05, 0x03, 0x00, 0x00} // 27 '
,{0x00, 0x1c, 0x22, 0x41, 0x00} // 28 (
,{0x00, 0x41, 0x22, 0x1c, 0x00} // 29 )
,{0x14, 0x08, 0x3e, 0x08, 0x14} // 2a *
,{0x08, 0x08, 0x3e, 0x08, 0x08} // 2b +
,{0x00, 0x50, 0x30, 0x00, 0x00} // 2c ,
,{0x08, 0x08, 0x08, 0x08, 0x08} // 2d -
,{0x00, 0x60, 0x60, 0x00, 0x00} // 2e .
,{0x20, 0x10, 0x08, 0x04, 0x02} // 2f /
,{0x3e, 0x51, 0x49, 0x45, 0x3e} // 30 0
,{0x00, 0x42, 0x7f, 0x40, 0x00} // 31 1
,{0x42, 0x61, 0x51, 0x49, 0x46} // 32 2
,{0x21, 0x41, 0x45, 0x4b, 0x31} // 33 3
,{0x18, 0x14, 0x12, 0x7f, 0x10} // 34 4
,{0x27, 0x45, 0x45, 0x45, 0x39} // 35 5
,{0x3c, 0x4a, 0x49, 0x49, 0x30} // 36 6
,{0x01, 0x71, 0x09, 0x05, 0x03} // 37 7
,{0x36, 0x49, 0x49, 0x49, 0x36} // 38 8
,{0x06, 0x49, 0x49, 0x29, 0x1e} // 39 9
,{0x00, 0x36, 0x36, 0x00, 0x00} // 3a :
,{0x00, 0x56, 0x36, 0x00, 0x00} // 3b ;
,{0x08, 0x14, 0x22, 0x41, 0x00} // 3c <
,{0x14, 0x14, 0x14, 0x14, 0x14} // 3d =
,{0x00, 0x41, 0x22, 0x14, 0x08} // 3e >
,{0x02, 0x01, 0x51, 0x09, 0x06} // 3f ?
,{0x32, 0x49, 0x79, 0x41, 0x3e} // 40 @
,{0x7e, 0x11, 0x11, 0x11, 0x7e} // 41 A
,{0x7f, 0x49, 0x49, 0x49, 0x36} // 42 B
,{0x3e, 0x41, 0x41, 0x41, 0x22} // 43 C
,{0x7f, 0x41, 0x41, 0x22, 0x1c} // 44 D
,{0x7f, 0x49, 0x49, 0x49, 0x41} // 45 E
,{0x7f, 0x09, 0x09, 0x09, 0x01} // 46 F
,{0x3e, 0x41, 0x49, 0x49, 0x7a} // 47 G
,{0x7f, 0x08, 0x08, 0x08, 0x7f} // 48 H
,{0x00, 0x41, 0x7f, 0x41, 0x00} // 49 I
,{0x20, 0x40, 0x41, 0x3f, 0x01} // 4a J
,{0x7f, 0x08, 0x14, 0x22, 0x41} // 4b K
,{0x7f, 0x40, 0x40, 0x40, 0x40} // 4c L
,{0x7f, 0x02, 0x0c, 0x02, 0x7f} // 4d M
,{0x7f, 0x04, 0x08, 0x10, 0x7f} // 4e N
,{0x3e, 0x41, 0x41, 0x41, 0x3e} // 4f O
,{0x7f, 0x09, 0x09, 0x09, 0x06} // 50 P
,{0x3e, 0x41, 0x51, 0x21, 0x5e} // 51 Q
,{0x7f, 0x09, 0x19, 0x29, 0x46} // 52 R
,{0x46, 0x49, 0x49, 0x49, 0x31} // 53 S
,{0x01, 0x01, 0x7f, 0x01, 0x01} // 54 T
,{0x3f, 0x40, 0x40, 0x40, 0x3f} // 55 U
,{0x1f, 0x20, 0x40, 0x20, 0x1f} // 56 V
,{0x3f, 0x40, 0x38, 0x40, 0x3f} // 57 W
,{0x63, 0x14, 0x08, 0x14, 0x63} // 58 X
,{0x07, 0x08, 0x70, 0x08, 0x07} // 59 Y
,{0x61, 0x51, 0x49, 0x45, 0x43} // 5a Z
,{0x00, 0x7f, 0x41, 0x41, 0x00} // 5b [
,{0x02, 0x04, 0x08, 0x10, 0x20} // 5c \
,{0x00, 0x41, 0x41, 0x7f, 0x00} // 5d ]
,{0x04, 0x02, 0x01, 0x02, 0x04} // 5e ^
,{0x40, 0x40, 0x40, 0x40, 0x40} // 5f _
,{0x00, 0x01, 0x02, 0x04, 0x00} // 60 `
,{0x20, 0x54, 0x54, 0x54, 0x78} // 61 a
,{0x7f, 0x48, 0x44, 0x44, 0x38} // 62 b
,{0x38, 0x44, 0x44, 0x44, 0x20} // 63 c
,{0x38, 0x44, 0x44, 0x48, 0x7f} // 64 d
,{0x38, 0x54, 0x54, 0x54, 0x18} // 65 e
,{0x08, 0x7e, 0x09, 0x01, 0x02} // 66 f
,{0x0c, 0x52, 0x52, 0x52, 0x3e} // 67 g
,{0x7f, 0x08, 0x04, 0x04, 0x78} // 68 h
,{0x00, 0x44, 0x7d, 0x40, 0x00} // 69 i
,{0x20, 0x40, 0x44, 0x3d, 0x00} // 6a j 
,{0x7f, 0x10, 0x28, 0x44, 0x00} // 6b k
,{0x00, 0x41, 0x7f, 0x40, 0x00} // 6c l
,{0x7c, 0x04, 0x18, 0x04, 0x78} // 6d m
,{0x7c, 0x08, 0x04, 0x04, 0x78} // 6e n
,{0x38, 0x44, 0x44, 0x44, 0x38} // 6f o
,{0x7c, 0x14, 0x14, 0x14, 0x08} // 70 p
,{0x08, 0x14, 0x14, 0x18, 0x7c} // 71 q
,{0x7c, 0x08, 0x04, 0x04, 0x08} // 72 r
,{0x48, 0x54, 0x54, 0x54, 0x20} // 73 s
,{0x04, 0x3f, 0x44, 0x40, 0x20} // 74 t
,{0x3c, 0x40, 0x40, 0x20, 0x7c} // 75 u
,{0x1c, 0x20, 0x40, 0x20, 0x1c} // 76 v
,{0x3c, 0x40, 0x30, 0x40, 0x3c} // 77 w
,{0x44, 0x28, 0x10, 0x28, 0x44} // 78 x
,{0x0c, 0x50, 0x50, 0x50, 0x3c} // 79 y
,{0x44, 0x64, 0x54, 0x4c, 0x44} // 7a z
,{0x00, 0x08, 0x36, 0x41, 0x00} // 7b {
,{0x00, 0x00, 0x7f, 0x00, 0x00} // 7c |
,{0x00, 0x41, 0x36, 0x08, 0x00} // 7d }
,{0x10, 0x08, 0x08, 0x10, 0x08} // 7e ←
,{0x78, 0x46, 0x41, 0x46, 0x78} // 7f →
};
void LcdCharacter(char character)
{
 LcdWrite(LCD_D, 0x00);
 for (int index = 0; index < 5; index++)
 {
 LcdWrite(LCD_D, ASCII[character - 0x20][index]);
 }
 LcdWrite(LCD_D, 0x00);
}
void LcdClear(void)
{
 for (int index = 0; index < LCD_X * LCD_Y / 8; index++)
 {
 LcdWrite(LCD_D, 0x00);
 }
}
void LcdInitialise(void)
{
 pinMode(PIN_SCE, OUTPUT);
 pinMode(PIN_RESET, OUTPUT);
 pinMode(PIN_DC, OUTPUT);
 pinMode(PIN_SDIN, OUTPUT);
 pinMode(PIN_SCLK, OUTPUT);
 digitalWrite(PIN_RESET, LOW);
 digitalWrite(PIN_RESET, HIGH);
 LcdWrite(LCD_C, 0x21 ); // LCD Extended Commands.
 LcdWrite(LCD_C, 0xB1 ); // Set LCD Vop (Contrast). 
 LcdWrite(LCD_C, 0x04 ); // Set Temp coefficent. //0x04
 LcdWrite(LCD_C, 0x14 ); // LCD bias mode 1:48. //0x13
 LcdWrite(LCD_C, 0x20 ); // LCD Basic Commands
 LcdWrite(LCD_C, 0x0C ); // LCD in normal mode.
}
void LcdString(char *characters)
{
 while (*characters)
 {
 LcdCharacter(*characters++);
 }
}
void LcdWrite(byte dc, byte data)
{
 digitalWrite(PIN_DC, dc);
 digitalWrite(PIN_SCE, LOW);
 shiftOut(PIN_SDIN, PIN_SCLK, MSBFIRST, data);
 digitalWrite(PIN_SCE, HIGH);
}
void setup(void)
{
 LcdInitialise();
 LcdClear();
 LcdString("Hello World!");
}
void loop(void)
{
}

• Peter Bloomfield: Welcome to Arduino SE. It would be helpful if you tell us the part number of the LCD screen, and also where you got the code for controlling it.
• user3211857: I second that. But be aware that some LCD boards, have a little plastic potentiometer on the back. If you turn the it, you can adjust the contrast.
• BSheep: First, thank you on greeting. I bought part here ebay.to/1ztRhd5 and (I did not know that fact) I checked and could not find any potentiometer on LCD screen. I am new to electronics, I did manage to do some things with LED diods, sound even some small theremin project, but LCD screen I just do not understand still. Code comes from this site playground.arduino.cc/Code/PCD8544

Answer 1

Have you even read your own code? Notably line 141; LcdWrite(LCD_C, 0xB1 ); // Set LCD Vop (Contrast)..

Try sending a different value. Note that the first bit should always be 1 so the value should be between 0x80 and 0xFF

• BSheep: Thank you. As I said I am new to electronics, and still figuring out this code. I did see this but did not know what to do with it. Can you help me with some thread or help where I can find out how to calculate these hex values?
• Gerben: You'll need a higher value I think. Just try a few different values. You can't calculate them, as the differ from display to display (and change due to temperature). In case you're not familiar with hex notation (0xB1), instead you can use a decimal number from 128 to 255. So e.g. LcdWrite(LCD_C, 190)
• BSheep: Actually if I am not mistaken that is contrast for background right? That will not make my letters more visible right?
• Gerben: No and no. here is a video showing different contrast values. It seems like you haven't even tried, so I'm out.

Answer 2

Backlight is connected through potentiometer.

You should try to turn the potentiometer.

If that doesn't work, there might be something wrong with the connection from the potentiometer to the Backlight.

---

Check out this video: https://www.youtube.com/watch?v=XR8ede6V6eA&t=65 Where the led would be replaced with the BL (black-light) pin.

• Chetan Bhargava: Backlight has nothing to do with contrast.

Answer 3

I assume you are using a 16 pin 16x2 display. Try wiring a potentiometer like this with the pot wiper on pin 3. This is what adjusts text contrast: enter image description here

• Chetan Bhargava: By looking at the code OP is not using a character LCD

Answer 4

Same problem, I solved it following this:

The contrast can be adjusted by the potential-meter displayed in the following picture.

enter image description here

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