Can't get the Displaytech 204A-CC-BC-3LP working

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.

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

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

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.

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:

/* 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.

Setup 1.JPG

Setup 2.JPG

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

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

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!

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.

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!

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

Faulty wiring.

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?

Maybe a dodgy breadboard?

I wish I had thought of that!

Don

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!

Sometimes an LCD can have a decent contrast when the contrast pin is pulled to GND. So if your pin 3 was connected to a data pin during the pin order reversal, and that pin is pulled to GND, you could see the blocks though. Good thing you found your problem.

I know this is an old post but it's likely the issue was the display was not reset. If you are running in 4 bit mode and get out of whack then your bytes will be reversed.

have a look at this datasheet it got mine going

https://cdn.displaytech-us.com/sites/default/files/display-data-sheet/202B%20series-v21.pdf

Try this datasheet this got my one working

https://cdn.displaytech-us.com/sites/default/files/display-data-sheet/202B%20series-v21.pdf

the supplier posted another datasheet and that got me thinking that i cannot get this done until i saw on the front of the panel the letters 202B googled it and found this datasheet

Very peculiar datasheet indeed!

Gives information about a number of versions of the display, and illustrates a peculiar pin numbering with the sequence 14 to 1, then 15 and 16 which may well be relevant to this whole discussion thread, but does not even illustrate the functions of the pins.

Paul__B:
Very peculiar datasheet indeed!

Gives information about a number of versions of the display, and illustrates a peculiar pin numbering with the sequence 14 to 1, then 15 and 16 which may well be relevant to this whole discussion thread, ...

... as I pointed out nearly six years ago in reply #5!

Don

Paul__B:
Very peculiar datasheet indeed!

Gives information about a number of versions of the display, and illustrates a peculiar pin numbering with the sequence 14 to 1, then 15 and 16 which may well be relevant to this whole discussion thread, but does not even illustrate the functions of the pins.

Peculiar indeed but it works when you read a bit further and maybe look at the pin definitions printed on the pcb another thing the pinouts on this screen is a bit different to the one on the original datasheet and it seems they changed it for some other reason than the actual pin functions but the pin functions remains the same just in another place

only thing that bothers me is that a I2C back pack doesn't work without a bit of cable in there