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16  Using Arduino / Displays / Re: LCD current draw on: July 20, 2014, 04:45:02 pm
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i just said what is thew maximum voltage for the back light to operate according to the data sheet !!!

You still don't understand the difference between a 'rating' and a 'characteristic'.  

Once again, the 4.6 volts is not the maximum voltage that you can or should apply to the LED.  Rather, it is the maximum voltage drop that will appear across any of this type of LED when it is operating within it's ratings.  

If you have a box full of these devices and you measure the voltage across each of their backlight LEDs when they are operating within their ratings you can expect to measure a wide range of voltages, but none of them should be more than 4.6 volts.

What this actually means is that when you are selecting a power source you must make sure that it delivers more than 4.6 volts if you want to be certain that you can get every backlight to function.



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The datasheet doesn't mention any current rating for the back light!!!

Did you look at reply #3 or #5?


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Also , something i didn't say before, i tried twice to turn on the back light ,at 4V, by pins 15-16 and nothing happened!!!!

Because, as explained above, you must use a supply greater than 4.6 volts (with a current limiting resistor) to be sure to be able to get the LED to conduct.


Don
17  Using Arduino / Displays / Re: trying to understand the crystal library library on: July 20, 2014, 02:28:25 pm
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well i understand what the digits on the right of the letter B are for , but not the letter B itself and the zero to its left
The initial zero is there to inform the compiler that this is a number.
The 'B' tells the compiler that this is a 'Binary' number.


Don
18  Using Arduino / Displays / Re: Can't figure out how to use special segments at bottom of LCD 8X1 display on: July 20, 2014, 11:09:40 am
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Code:
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

Is called a C++ constructor.
It is creating a global "object" from the LiquidCrystal class called lcd and the parameters
are being passed to the LiquidCrystal library and are used to fill in other data fields inside
that object.

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The library allows controlling more than a single instance of the hardware. (multiple LCDs)
Each instance would get its own object.

Let me try this without using any C jargon.  (Bill: Correct me if this simplification is incorrect)

The 'lcd' part of the statement is really what we are discussing here.  This is the name that the programmer has arbitrarily given to his display.  He could have just as well called it 'mario' or 'plugh'.

If your application calls for more than one display you can control any or all of them using the same library.  You would differentiate between them by giving each a display different name.


Code:
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
LiquidCrystal mario(12, 10, 5, 4, 3, 2);
LiquidCrystal plugh(12, 9, 5, 4, 3, 2);

For a complete example see this thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1265969050

What Bill is saying is that his code snippet only works with one display and you must use the name lcd for that display.  It's as simple as that.


Don

Edit: If you wind up in a cave it isn't my fault.  If you don't understand this disclaimer then don't worry about it, your hair probably isn't grey either.
19  Using Arduino / Displays / Re: LCD current draw on: July 20, 2014, 10:31:14 am
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However it's not the same for the back light which has a maximum of 4.6V.
You don't really understand the datasheet.  The voltage to which you refer is not a rating, it is a characteristic.   

You do not apply a specific voltage to an LED, instead you apply enough voltage to get it to function and then you limit the current to its rated value, typically with a series resistor.

When the current through the LED has been limited to the proper value you can then measure the voltage across the LED and it should be somewhat near the value in the datasheet.


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LCD 5V, Back light never lighted through pins 15-16, instead it destroyed some pixels.. Back light was ok through A and K on 3.3V and about 4V(external power source)...
You may have damaged the backlight by applying a non current limited voltage directly to the A and K backlight pins but the destruction of any pixels is unrelated - unless you inadvertently applied the voltage elsewhere as well. 

Don
20  Using Arduino / Displays / Re: LCD black boxes problem! on: July 19, 2014, 11:52:55 am
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I have tried all of the above but still no good.
Show us what the set-up and the display look like after step (2).

Don
21  Using Arduino / Displays / Re: 2004 LCD partially doesn't work on: July 19, 2014, 09:16:50 am
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It is possible, during i2c scanning, ...

Where did the original poster mention anything about I2C?

Don
22  Using Arduino / Displays / Re: Displaying date on LCD with DS1307 using button inputs on: July 18, 2014, 04:25:51 pm
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Okay. So what would be the cause of this conflict?
The conflict is that you have chosen to use the same pin for both the push-button and for the LCD.

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Bad = Pins 2,3,4,5,11,12,13
Pins 2,3,4,5,11,and 12 are 'bad' because you are already using them for the LCD.
Pin 13 may be bad because the on-board LED is connected to that pin.


Don
23  Using Arduino / Displays / Re: Lcd missing pixels on: July 18, 2014, 04:20:38 pm
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im gonna buy a new one. it was cheap anyway ... I still can't understand how it happened !!
Try to find one that is inexpensive but not cheap.

Don
24  Using Arduino / Displays / Re: LCD black boxes problem! on: July 18, 2014, 04:16:46 pm
Here is my generic step by step approach that should work:

(1) If the module has a backlight then get it working properly.  This involves only pins 15 and 16 on most LCD modules.  Make sure to use a current limiting resistor if there is none on the LCD module.

(2) Get the power and contrast working properly.  This involves only pins 1, 2, and 3 on most LCD modules.  You should be able to just barely see blocks on one row of a two row display and on two rows of a four row display. 

NOTE:  The Arduino has not been used yet, except as a possible source for the power needed for the first two steps.  Do not try to go any further until this is working.  If you don't see the blocks then no amount of program code will help.

(3) Connect the LCD R/W pin (pin 5) to GND.

(4) Connect the six control and data wires between your LCD module and your Arduino.

(5) Upload your sketch and it should work.


Troubleshooting:

If you have a 16x1 display and there are blocks only on the left half of the row in step 2 then use lcd.begin(8, 2); in your sketch.

If you still don't get a display then make sure that your wiring matches the numbers in the descriptor (or vice versa).


Code:
//LiquidCrystal lcd(RS, E, D4, D5, D6, D7);
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);      // put your pin numbers here

If you get a display but it is garbled or has some other problems then try again with a 'static' sketch, one that displays a simple message on the top row of the display and then stops.  All of your code should be in setup() and loop() should be empty between the brackets.

Code:
#include <LiquidCrystal.h>

//LiquidCrystal lcd(RS, E, D4, D5, D6, D7);
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);      // put your pin numbers here

void setup()
  {
  lcd.begin(16, 2);                          // put your LCD parameters here
  lcd.print("hello, world!");
  lcd.setCursor(0,1);
  lcd.print("it works!");
  }

void loop()
  {
  }

If you are still having problems then we need to see a photograph of your setup that clearly and unambiguously shows all of the connections between your Arduino and your LCD module.  We also need a copy/paste version of the code that you are actually using, not a link to the code that you think you are using.

Don


25  Using Arduino / Displays / Re: Displaying date on LCD with DS1307 using button inputs on: July 18, 2014, 10:59:38 am
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Any insight or explanation as why this happened would be great.
Because there is a conflict in the use of pin 11. 

Don
26  Using Arduino / Displays / Re: How to underline (indicate) a character on HD44780 LCD without delay() use? on: July 18, 2014, 10:54:38 am
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I didn't use any libraries for interface handling. LCD is controlled with LiquidCrystal.h.
That's not the way I interpreted your original post.

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Can you be more specific with your advice?
Not really.  I was under the impression that you were controlling your LCD using code that you had written that did not involve using the delay() routine and was confused about why you would then consider using cursor() and noCursor().

Don
27  Using Arduino / Displays / Re: How to underline (indicate) a character on HD44780 LCD without delay() use? on: July 17, 2014, 12:28:52 pm
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I didn't use any libraries because the interface is quite simple and decided to code everything on my own.

Since you have already coded everything else without using a library why do you think you have to use the cursor() and noCursor() functions?

The underline and blink are both handled by the 'Display on/off control' instruction.  All you have to do is issue your own version of this instruction and then deal with the required delay using whatever method you used in your other routines.


Don
28  Using Arduino / Displays / Re: Newline char causes odd character on SainSmart 2004 20x4 I2C LCD on: July 17, 2014, 09:23:09 am
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So i will keep that "fancy" chinese char, not a problem, only esthetic.

You might be able to get rid of it by creating a 'blank' custom characters at the appropriate address.

Don
29  Using Arduino / Displays / Re: LCD current draw on: July 17, 2014, 09:02:20 am
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A thousand apologies, my bad for reading too quickly

I do that frequently as well.

Getting back to your original post:

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It says "LED" but it also says "EL", so I suspect the backlight is really electroluminescent.

If you look at the diagrams at the top of the page it appears that there are several different versions, LED backlight, EL backlight, and no backlight..

Don
30  Using Arduino / Displays / Re: LCD current draw on: July 17, 2014, 08:47:43 am
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Most of these units draw about 20 mA or so, I just went and measured it - about 151 mV across the "101" - 100 ohm resistor R8 on the one next to me which would be 150 mA but the USB supply is loaded down to 4.55V by all the junk I have connected.  Which means you can probably  control it directly from an Arduino pin.

This agrees with my experience as well.

When you do the math with the numbers that I (and Jack) supplied you will find out that the required resistance to give the nomnal current is in the order of 7 ohms.   Since most of us use a much larger resistor, typically at least 100 ohms (as on the board investigated by Paul) the actual LED current is much lower than that mentioned in the datasheet and the backlight is still quite bright.  You should have no trouble powering it directly from the Arduino.


Don

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