Need Help LCD 16x2

[chin0609]

the pic16f877a build connection should be no problem i can run other application such as motor ,led ...except LCD

here my LCD JHD162A
http://imageshack.us/photo/my-images/266/20110916114549.jpg/

my connection to pic, does the preset connect correct in the pin vee?
http://imageshack.us/photo/my-images/252/20110916120556.jpg/

[PCM programmer]

I didn't see anything that looked obviously wrong. But the LCD photo is a
double exposure and I can't see fine details on it. On the breadboard
photo, many of the wires go off-screen and I can't really tell where they
are going.

I think you should check all the LCD connections with an ohmmeter. I
noticed one pad on the LCD that appears to be mostly missing. Is there
really a good connection there ? Some of the solder joints on the LCD
pads appear to be very close to each other. Could they be shorted
together ?

I don't understand your trimpot circuit for LCD contrast. It appears to
be a trimpot sitting on the breadboard, with one wire (only) coming off
the center-tap of the trimpot. That won't do anything, by itself. One end
of the trimpot should connect to +5v, and the other end should connect
to Ground. Then it should be adjusted for 0.5v (That's 1/2 a volt),
by putting a voltmeter across the center-tap and the ground pins. The
center-tap should be connected to the contrast pin on the PIC. Maybe
this is your entire problem - no real contrast circuit. Fix that first.

One last thing. You should change the way you make breadboard circuits.
Use red wires for the +5v. Use black (or maybe green) for ground.
Don't use red or black wires for anything else. Then use other colored
wires for normal connections. That way, it's very easy to see if the power
and ground connections are present, and correct. Also, try to keep
connections very short. Your wires are generally too long.

[temtronic]

Do yourself a HUGE favour..buy a roll of 10 conductor, 22ga. solid wire !
That way you'll have 10 different colors to use making it very very easy to troubleshoot breadboard circuits.
In the case of LCD wiring I use brown for pin 11, red for 12, org for 13 and yellow for 14,yellow for 4 and blue for pin 6. It's a logical sequence that allows it easy to follow the wiring.
I've already proved it is not your code so it's probably your wiring of the LCD or a broken LCD.
Like PCM Pgmr says, keep the wiring short, neat and tidy.....

[temtronic]

Also...
I have soldered 'wire wrap' pins onto my LCD, allowing it to use the lower right section of the breadboard. This allows for solid mechanical support of the LCD as well as easy connections to data, control and power pins.
My PIC16F877 is located on the left side, making it easy to remove for programming in my PicstartPlus unit. Wiring is 'neat and tidy' with very little chance of any wires coming out by mistake.
I have a second breadboard attached above this 'processor/lcd' unit, that usually has RS232 drivers, Vinculum, LEDs, temp sensors, etc.
Again it makes for easy to see...easy to check wiring.

[chin0609]

i think is the contrast problem.
can teach me how to connect the 3pin preset? which is connect to ground,5v and output?

[PCM programmer]

I said how to do it in my post. But here is a diagram.
Look at the blue trimpot:
http://arduino.cc/playground/uploads/Code/LCD3wiresSchematic_new.jpg

Disregard the HEF4094.

[chin0609]

ya my trimpot 3 pin (top2 bottom 1) which is them? the diagram you show me is 3pin in a same line.

[Ttelmah]

No, it does not have '3in in a same line'. It has the top pin of the trimpot going to 5v, the bottom pin of the pot going to 0v, and the wiper, connected to the contrast pin on LCD. The contrast pin will normally want a small voltage of about 0.5v, so if the trimpot is set about 1/10th the way from bottom to top, this will be the voltage generated at the contrast pin. Many modern LCD's, will give a reasonable display with anything from about 0v to 0.6v on this pin. However for the best display, it _does_ need to be adjusted. This is why things using these displays often have a software setting to adjust the voltage (using a digital trimpot, instead of the mechanical one).

Best Wishes

[chin0609]

[temtronic]

Using your picture as a reference...

Left terminal of pot goes to +5v volt.

Right terminal goes to ground.

Center terminal goes to LCD Vee (pin 3).

Adjust pot to give best contrast, usually it'll be about .5Volts.

Once you measure the VEE, you can replace the pot with 2 resistors as a voltage divider. For my LCD and contrast that consists of a 20K tied to +5 and Vee pin and a 499R tied to VEE pin and ground.

[chin0609]

[PCM programmer]

Please stop this. This thread has gone on for 2x or 3x longer than
it should have.

Based on your description, the trimpot pins look like this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=3386P-103LF-ND

That means the 3 trimpot pins should be connected like this: