LCD(topway lmb402cb) backlight on but no text !!

Hey guy ive been trying to get a simple hello world message on my new LCd the last day and all i can get so far is backlight. I have no idea what im doing wrong . Heres my layout the potentiometer im using is a 10k one but ive also tried a 5k one with no joy.

Starting to annoy me now at this stage should be basic.

// include the library code:
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print("hello, world!");

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
  // print the number of seconds since reset:
  lcd.print(millis() / 1000);

There is my code.

Any ideas on what im doing wrong ? I included the library in the first line is there something else i should download from arduino website though ? im not getting any erros in my code either.

There is no resistor on the backlight in your diagram.

i read on a previous post that the topway lcd dosnt require a series resistor.I have tried putting a 220k resistor as seen on the liquid crystal example on this site ut when i do this the back light dosnt even come on :o :o

OK, check the voltage supplied to the LCD at the LCD power input. Some breadboards have a split in the power rails that needs to be jumped so that both ends of the rail gets power. Could you post a photo of your actual set up?

Does that empty post mean still no text? :frowning:

Heres my setup , exact same as one in first post

Did you check the supply voltage? I don't know what else to try.

Just fiddling around with the 5k pot and managed to get some black lines at the bottom of the screen.
Also connected resistor to backlight and got a flash of black boxes then nothing. this was meant to be basic example lol

Just fiddling around with the 5k pot and managed to get some black lines at the bottom of the screen.

Black lines??

Without using any code, your first milestone is to hook up the power, ground, contrast pot and backlight power and ground. The back light should be running. With adjustment of the pot, you should be able to see black or white boxes on one two rows of the display. The contrast setting should be able to change the appearance of these boxes.

Can you post a photo of the "lines". Can you get to black or white boxes?

Here it is without 220kohm resistor to back light

Here it is without resistor

when i turn potentiometer the black lines go away. :confused:

I would have preferred to see a photo with only 5 wires connected. Did you do that with no code running?

Clearly,the backlight is working, and there must be some power to the display to see the lines. Did you check the supply voltage as suggested in #7.

If this is what you see under those circumstances, I would still have to say that unfortunately, it looks like a defective display. No boxes, and the presence of the lines on only one half of the display is particularly disturbing.

when i turn potentiometer the black lines go away. :confused:

Do they fade, or just disappear?

One more thing to do would be to replace the pot with a simple jumper/resistor from pin3 to ground. Start with a jumper, and then try a few values like 470, 1k and 2.2 K. Can you see any difference in the black lines turning to boxes or turning to white?

Was this display purchased with the header pins soldered? The soldering looks pretty good, but perhaps a photo just focused on the connection quality might show me something.

You could also try change the position of the display in the breadboard and the connecting wires as sometimes they are defective.

Tried using 10khom resitor and still nothing. not even backlight is showing up with this setup.

I done the soldering myself i dont think the problem is with that. also the LCD is new so i dont think it could be faulty im probably doing something wrong but not seeing it.

With the use of the pot the black lines fade away

From looking at the datasheet ( ), it looks like it does not require a resistor. The basic schematic shows 28 diodes and what looks like a resistor. It also lists the forward voltage of the backlight as 5v which sort of implies an embedded resistor. Even if it didn't have a resistor, the 220k resistor he says he tried is WAY to high - something like 220 ohms (or even 22) would have been more appropriate for a backlight that does not have a built in resistor.

I agree with @gpsmikey that the backlight does not require a resistor as one was shown in the data sheet. Can you show a photo of the back of the display? I believed that a resistor in R8 or R9 is typically connected to the backlight. Again, an additiional 220ohm should be enough to slightly dim the backlight if you want.

Tried using 10khom resitor and still nothing

Regarding the connection of pin3 to ground without the pot involved, 10K is too large. Typically, the proper contrast will be seen with 2.2K or less.

Heres back of display.

Ive wired and re-wired the connection at least 30 times now at this stage and still nothing.
Also what do you mean by check power supply ? im powering the lcd via the arduino 5v. The backlight comes on sometimes so i think there is power.

using a 4.7kho pot currently. Can you see from my previous posts that its hooked up correctly ?

using a 4.7kho pot currently. Can you see from my previous posts that its hooked up correctly ?

Like, I have been suggesting, simply a resistor from pin 3 to ground will eliminate any issues with the pot.

You can try using the pot without hooking up the leg to 5v. Just use the wiper and the ground. You should be able to vary the resistance that way. It's interesting that the data sheet actually shows the use of a variable resistor to ground. The use of a powered potentiometer instead of a resitance(variable or not) to ground is common, but not necessary.

The presence of the lines on only half the display indicates a hardware problem to me. Try pressing on the black blobs on the back of the display(they are the encapsulation for the controller chips) and see if that changes where the black lines appear. Also try pressing the display itself as there is a pressure contact made between the screen itself and the controller.