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61  Using Arduino / Displays / Re: LCD current draw on: July 21, 2014, 07:24:19 pm
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...as i posted before, the back light works fine through "A" and "K".
It's probably nice and bright also.  It is most likely the limited capacity of the power source that has prevented your backlight from self destructing.

Look at the circuit diagram on page 19 of the datasheet.


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Should the back light turn on, if i connect pins 15-16 to power and ground , but with nothing else connected on the LCD ?
Yes, but without a current limiting resistor you are again relying on having a power supply with limited capacity to prevent your backlight from being destroyed.
No.  Look at page 6 of the datasheet.  Pin 15 is used to provide a negative voltage to ultimately drive pin 3, and pin 16 is not used.

Look at page 7 to see how to connect your contrast potentiometer.  One end goes to +5v, the other end goes to pin 15 (not GND), and the center goes to pin 3.


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Because i  applied 5V on pin 15 and grounded pin 16, i didn't wire anything else at the LCD, and the back light didn't turn on !!! Should it ?
Same question --> same answer.

Don
62  Using Arduino / Displays / Re: LCD current draw on: July 21, 2014, 07:15:33 pm
So now that we know the real part number of the display (RC1602B-YHY-CSVD) we can look at the datasheet and get information about the backlight (in section 14 on page 19).

The 'note' on that page says this:
Note:  The LED of B/L is drive  by current only,  Drive voltage is for reference  only.  Drive voltage can make driving current under safety area (current between minimum and maximum).

This is entirely consistent with what I posted in reply # 19.  Basically, after you get past the fractured English, it is saying that the important consideration is the current rating.  If you try to drive it with a voltage source you may get too little current (and it won't light) or too much current (and it will light brightly, for a relatively short period of time).

Don
 
63  Using Arduino / Displays / Re: LCD black boxes problem! on: July 21, 2014, 02:02:08 pm
That is what the LCD display should look like after step 2 although your backlight looks quite bright.

Now go ahead with steps 3, 4, and 5.


Don
64  Using Arduino / Displays / Re: My lcd only show squares on: July 21, 2014, 01:57:35 pm
Your display has serious problems most likely due to poor connections between the LCD 'glass' and the pc board. 

These connections are made by 'zebra strips' and there have been numerous threads with information about them.

The search capabilities of this forum software is abysmal, even if you find the camouflaged search box.  Try the following Google search: "LCD zebra site:arduino.cc".


Don
65  Using Arduino / Displays / Re: 16x2 goes blank after few hours. on: July 21, 2014, 08:52:19 am
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On several occasions I had the idea that the LCD went blank right after it turns of a relay which is powering an exhaust fan. Not sure if its related,  I just noticed it.

You should pursue this a bit further.  Temporarily replace your relay (and any other inductive devices you are controlling) with an LED and I think you will find that your problem goes away.

Don
66  Using Arduino / Displays / Re: Something wrong to my lcd to arduino on: July 21, 2014, 08:47:11 am
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Those things have a memory, and can sometimes display the last junk that went to them whilst the wires were being pulled out by a shaky hand.
All of the LCD memory is volatile.  Although the display will remain if the data and/or control lines are disconnected it will not survive having the power removed.  Not even for a few seconds much less a few weeks.

Don
67  Using Arduino / Displays / Re: LCD not displaying eveything on: July 21, 2014, 08:40:44 am
The lcd.println() statement is going to give you problems even if you get everything else sorted out.

Don
68  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
69  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
70  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.
71  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
72  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
73  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
74  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
75  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
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