I am trying to use this screen (http://www.newhavendisplay.com/specs/NHD-0216SZ-FSW-FBW.pdf) in 4-bit.
Backlight is lit, and I have a good 5V on Pin 2. Pin 3 is changing voltage when I adjust the 10k pot, but absolutely nothing changes on the screen itself. (For troubleshooting, all of the other pins are disconnected)
I’ve read some things about pins on the rear of certain LCDs requiring connection; since I cannot get a row of blocks on this screen, I’m assuming something with either logic or contrast is messed up.
Any advice on how to approach here? I hate thinking that this is a hardware issue, but nothing I do here shows any contrast on the screen at all and I therefore have no clue if logic is working.
I’ve found that SOME LCD displays (Optrex, so far) require a NEGATIVE voltage on the Vee pin (about -3.3 volts). Simply tying Vee to ground will not give you a display (if yours is like the Optrex that needs a negative Vee).
To test if this is the problem, get two AA cells or a lithium coin cell (the 3.6 volt kind). Connect your AA cells in series to make a 3 volt battery (or use the coin cell) and connect the POSITIVE side to the LCD ground and connect the NEGATIVE side, through a 100 ohm resistor (just to be safe) to Vee.
You don’t even need to have the LCD connected to the Arduino… just give it power, ground and -3 volts Vee.
If it works, you will get one line of dark blocks on the display.
Then you can go on and connect it to the Arduino and see if it will display characters.
If it works… now what? Where do you get -3 volts?
Answer: From your Arduino!
(click pic for full size)
Use this circuit to generate about -3.5 volts DC which you can then run to the contrast pot of the LCD.