I am having the same problem with the 202B DisplayTech LCD (202B-GC-BC-3LP). I have checked all of the supply voltages and they all seem acceptable according to the data sheet.
Parameter Symbol Condition Min Typ Max Unit
Supply voltage for logic VDD --- 4.5 5.0 5.5 V
Supply current for logic IDD --- --- 0.92 3 mA
Operating voltage for LCD VDD - VO 25°C 4.5 4.8 5.1 V
Supply voltage for LED Backlight VF --- 3.4 3.5 V
The following connections are made from the LCD:
Pin 1 (Vss) -> GND
Pin 2 (Vdd) -> 5V
Pin 3 (Vo) -> Wiper of 10k potentiometer connected between 5V and GND
Pin 4 (RS) -> Arduino pin 11
Pin 5 (R/W) -> GND
Pin 6 (E) -> Arduino pin 12
Pin 15 -> 150 ohm resistor -> 5V (backlight is visible and within tolerances)
Pin 16 -> GND
I am aware that I haven't yet connected the data lines; most tutorials say that by now I should be able to get one line of black boxes on the 20x2 LCD by varying the contrast. Since the minimum operating voltage for the LCD is (VDD - Vo), and VDD = 5V, VO must be less than 0.5V. Varying the voltage between 0V and 5V however does not produce anything on the screen (nor does varying Vo beyond 0.5V).
Have I missed something crucial? Any help would be very much appreciated as I have now spend the whole afternoon trying to get any sign of life from the LCD! (excluding the backlight).
Thanks in advance.