# Problem interfacing with an lcd with an arduino

My lcd arrived today and i saw that when i connect the backlight pins (A and K) to GND and +5V, the backlight turns on, but i cannot control it with the potentiometer. The wiring seems fine (ive checked and rechecked). Also, the 'hello world' sketch from the arduino website does not seem to be working at all. Any suggestions?

• The potentiometer probably controls the LCD contrast, not the backlight. If you turn the pot to one extreme, you should get black blocks on the screen, and at the other extreme, the display will be blank. I assume you've connected power and data to the LCD? – Peter Bennett Mar 27 '15 at 19:32
• The lcd is displaying a bright green backlight. No blocks are seen even when i turn the potentiometer to both the extremes – Arjun Monga Mar 27 '15 at 19:36
• Schematic of how you've got it connected? – brhans Mar 27 '15 at 19:59
• The Arduino library probably needs to be configured with correct pins used by the display shield. You'll have to find the datasheet for you specific shield and find the paragraph that lists the pin out. In your code look for a line like Look for a line like LiquidCrystal lcd(8, 9, 4, 5, 6, 7); arduino.cc/en/Reference/LiquidCrystalConstructor – jippie Mar 27 '15 at 20:01

You need to check a few things.

1) What voltage rating is the LCD? Most LCD displays require +5V power supply.

2) What voltage is the processor on your Arduino board running at? These can be either 3.3V or 5V.

If your Arduino board is running at 3.3V and you are trying to run a 5V LDS display from it without using level conversion, it probably won't work.

3) Does the display change at all as you rotate the contrast pot? FWIW - the voltage on the contrast line is usually fairly close to ground.

4) How have you connected the display to the Arduino? You need a minimum of 6 lines: data lines 4-7 plus EN & RS. Just connect the R/W line from the LCD to ground for now.

5) Is your LCD rated for operation at cold temperature? If so, you may need to bring the contrast line below ground (negative). It doesn't need to be much below ground and you should still see something on the display with the contrast voltage set to 0V - but you may need to do this if you can't get enough contrast on the display when you get it working.

6) Is your Arduino sketch known-good working code?

7) Are you actually getting your code into the Arduino? Maybe do a flashing LED from one of the port pins to ensure that your programming environment is working.

• well, the lcd is built to be used for hobbies(the site ssaid so). the display did not change a single bit when i rotated the pot. the lcd's backlight is working perfectly well, only the blocks cannot be seen. tcd is connected to the 5v pin on the arduino, so i dont think the voltage is faulty... – Arjun Monga Mar 27 '15 at 19:40
• Do you have the power and ground for the LCD logic connected - that is usually a separate pair of terminals from the backlight. – Peter Bennett Mar 27 '15 at 21:56
• Probably best to go back to the basics first. Use some code that makes a LED flash at the port pins of the Arduino. When you have that working, we can progress to finding out why the LCD doesn't work. – Dwayne Reid Mar 28 '15 at 5:08
• I mentioned this before but I'll ask again: what voltage does your Arduino run at? 3.3V or 5V? This does matter and we need to know. – Dwayne Reid Mar 28 '15 at 5:09