# LCD only turns backlight on - No Text

I just bought the LCD from sparkfun below: http://www.sparkfun.com/products/709

I am just trying to the hello world from the examples but I can only get the LED backlight to come on. What do you think is wrong? I have the D4-D7 connects to digital pins 5-2. Pin 2 to 5V, Pin 1 & 5 & 16 to GND, pin 3 to pot, pin 4 to digital 12, pin 6 to digital 11, and pin 15 connected to the pot for 4.2V (I haven't turn the pot because I wasn't sure how else to get 4.2V.

What should I look at?

What should I look at?

Everything you have said, it sounds like some connections are not being made.

spin the pot, the contrast may to too low or too high to see anything. Also try the reset button once the LCD has had a chnace to initialise, it took about a minute on mine.

The potentiometer is used to adjust the contrast by varying the voltage at pin 3. The typical voltage required for a legible display is almost always less than 1 volt, frequently much less. One typically uses a series resistor to get the required backlight current. You do not want to apply 4.2 volts to the backlight as this voltage is dependent on the current. You want to use a series resistor that will limit the current to the desired value (120 mA) and then the LED voltage will turn out to be about 4.2 volts. If you divide the desired voltage across this resistor (5 - 4.2 = 0.8V) by the desired current through it (0.120A) you get 6.67 ohms. I would start with a 10 ohm resistor.

Don

Will need pics showing how connections are made on both the LCD side and your arduino side. Just try this one, when you pull out connection to lcd pin 1, does the back light go out? And also this, when you turn your potentiometer, do you see black squares/text?

Looks like I have the contrast voltage too high. I used another pot for the contrast and its working now. It looks best on 1-1.3V. Also, can't I use the analog in pins and set them as outputs so I can set this voltage in the code? What would that look like?

rpmccly: Looks like I have the contrast voltage too high. I used another pot for the contrast and its working now. It looks best on 1-1.3V. Also, can't I use the analog in pins and set them as outputs so I can set this voltage in the code? What would that look like?

Most often you see flicker results if you do this without some low-pass filtering. I wouldn't recommend controlling contrast with a pin at all. Once set, the contrast should be left alone!

So what should I use for contrast resistor then since we don't have a current rating?

You don't use a fixed resistor here you use a potentiometer, typically 10K but not at all critical. There's a diagram at the bottom of page 2 of the extended datasheet. Have you seen the tutorial at http://www.ladyada.net/learn/lcd/charlcd.html?

Don

Also, can't I use the analog in pins and set them as outputs so I can set this voltage in the code?

No when you turn an analogue input into an output it turns into a digital output, not an analogue one. The only analogueish outputs are the PWM outputs. http://www.thebox.myzen.co.uk/Tutorial/PWM.html