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Topic: Can't get the Displaytech 204A-CC-BC-3LP working (Read 3664 times) previous topic - next topic

ttautkus

Good day everyone. I am not a very advanced user and I got a real problem.. I have got the Displaytech
204A-CC-BC-3LP (built on the KS0066U chip). I wired it as a standard 4bit parallel LCD but except the backlight can't get any sight of live from it - it just remains blank. Thought that i have fried it, so bought another one - same problem. Did anyone have managed to get same LCD working? I am just a programmer (so might not understand the high end teckie talk) please go ease on me;))

Thank you in advance!

liudr


dhenry

Quote
it just remains blank.


When those chips are properly powered up / contrast set right, you will see either your text (in the case that the lcd is properly initialized) or a line of black boxes (in the case the lcd is not properly initialized).

So your problem is either power or contrast.

mm8154

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.

floresta

Quote
Since the minimum  operating voltage for the LCD is (VDD - Vo), and VDD = 5V, VO must be less than 0.5V.

But the maximum operating voltage for the LCD could be 5.1 volts which would put VO at a negative value.  Typically a negative value is only needed for the extended temperature LCDs but it is still a possibility for yours.

To check this out all you have to do is disconnect the GND end of the potentiometer and connect it to the negative terminal of a battery.  Connect the positive terminal of the battery to GND and you can now vary VO from +5 to -whatever size battery you used.


Don


floresta

#5
Nov 14, 2012, 02:58 am Last Edit: Nov 14, 2012, 03:01 am by floresta Reason: 1
I just remembered that at least some of the Displaytech displays have their terminals at the lower left of the display.  Many displays with the terminals in that location have a non-standard pinout, typically 14, 13 .... 2, 1, 15, 16 instead of 1, 2, .... 15, 16 (reading left to right).  Perhaps you have one of those in which case you could be using the data pins in place of the power and control pins.

Don

mm8154

Don - thank you very much. Your second post was exactly right - I maybe should have noticed the tiny numbers on the datasheet but it certainly wasn't obvious for me! All sorted now.

Cheers.

mm8154

One more thing...

I am now failing to initialise the LCD. I have included a photo of my setup and have checked all pin connections and as far as I can tell they are all OK. The single line of black boxes at the top of the LCD never change. The datasheet for the LCD can be found here: http://www.displaytech.com.hk/upload/product/attachment/5287-202B.pdf (page 7).

My sketch is as follows:

Code: [Select]
/* LiquidCrystal(rs, enable, d0, d1, d2, d3, d4, d5, d6, d7) */
LiquidCrystal lcd(3,4,5,6,7,8,9,10,11,12);

void setup()
{
  delay(100);
  lcd.begin(20,2);
  lcd.clear();
  lcd.print("Hello world");
}

void loop() {}



Any help would again be very much appreciated.

Thanks.





floresta

My first reply seems to have been eaten by the Arduino server.

Quote
Any help would again be very much appreciated.


It's probably too neat.  You should use wires that are all the same color and then twist them around like spaghetti.  You have a good start there with the +5 and GND leads coming from the Arduino to the breadboard.

Your connections look OK as does the sketch.  You don't need the delay or the clear but they shouldn't keep it from working properly.

I haven't seen anyone use the 8-bit connection in a long time and never since the introduction of v1.0.  Maybe they broke this library along with introducing the other incompatibilities that have shown up.  Why don't you try
LiquidCrystal lcd(3,4,9,10,11,12); and see what happens?

Another long shot would be a bad solder connection or a bad breadboard connection.

Don

mm8154

My obsessive neatness is rarely a good thing, but hopefully it helped you understand the wiring on the breadboard! I have checked the connections from the arduino pins to each pad on the LCD and they all seem to be good. I had already tried using the LCD in 4-bit mode, and unfortunately it didn't work the second time around either. The sketch without the delay() and clear() yields the same response. Maybe it is time to get another LCD and test my current circuit with that... Thank you anyway!

liudr

If you flip your display around to see the bottom of the display, is there an indication of which pin is pin 1? I suspect you hooked up your display the wrong way, pin 1 was mistaken as pin 16. If you did it that way, you will still see the row of blocks, believe it or not.

mm8154

Well, I reversed the LCD pin order, and it didn't respond at all (not even the blocks appeared). I imagine it had to of been the correct orientation originally as otherwise the contrast adjustments wouldn't have been working.

However, believe it or not, after turning the LCD back around to its original position, "Hello world" magically appeared!!! Apart from a few missing dots in the first character (which presumably must be a hardware fault), I have a working LCD!

Thank you again for the help. I don't think I will ever know why it decided to work!

dhenry

Quote
I don't think I will ever know why it decided to work!


Faulty wiring.

mm8154

Thank you for the input, but the wiring is identical to the photo I posted earlier when the LCD wasn't working. Maybe a dodgy breadboard?

floresta

Quote
Maybe a dodgy breadboard?


I wish I had thought of that!

Don

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