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16  Using Arduino / Displays / Re: LCD always gives black boxes.. on: August 16, 2014, 10:08:41 am
You must not use the port pins denoted "0-RX" or "1-TX" on the Arduino ...

As I mentioned in the very first reply it is not a good idea to use those pins but "must not use" is overkill.  If you are out of available pins you can frequently use pins 0 and 1, depending on what you are trying to use them for.  

In this case I am pretty sure the LCD will work (if all the other problems are resolved) if you disconnect it while downloading the code and then reconnect it afterwards.

17  Using Arduino / Displays / Re: new LCD display not properly showing text on: August 16, 2014, 08:31:33 am
I've read another forum talking about setting the LCD baud rate to my serial monitor rate, but i'm not sure how to do any of that.

That information is not applicable in your case since you are not using a serial adapter between your Arduino and your LCD.

18  Using Arduino / Displays / Re: new LCD display not properly showing text on: August 16, 2014, 08:26:17 am
Why do you use the pins: 12, 11, 5, 4, 3, 2 ?
The examples on that website use: 8, 9, 4, 5, 6, 7
Good point.

My normal answer would be that you can use any available Arduino I/O pin for any of the LCD control or signal lines, but that is only true when you are doing the wiring between the two devices.

In this case the original poster did not tell us that he was using a shield.  In that case the wiring between the two devices has already been done and your constructor (LiquidCrystal lcd(...)) must match that wiring.

My original comment about moving the code from loop() to setup() still stands.

19  Using Arduino / Displays / Re: new LCD display not properly showing text on: August 16, 2014, 08:17:48 am
Move the code that you have in loop() into setup() and leave loop blank between the braces (for now).  Also, you don't need the lcd.clear in setup.

20  Using Arduino / Displays / Re: LCD always gives black boxes.. on: August 16, 2014, 08:12:55 am
It's time for a new photograph.

21  Using Arduino / Displays / Re: Clear Disaply but not position on: August 14, 2014, 08:32:26 pm
I didn't read the link, but doesn't it matter what size display (as in number of characters) you're controlling ?

You wouldn't be asking the question if you had read the link !

The LCD controller has 80 bytes of RAM corresponding to the largest display it can handle (20x4 or 40x2).  On the smaller displays not all of the RAM is used unless you do some display shifting (which is called scrolling in Arduinoese) but it is still there.

22  Using Arduino / Displays / Re: LCD always gives black boxes.. on: August 14, 2014, 08:27:37 pm
So is it normal that black boxes appearing on lcd display?

Yes and no.

The presence of the boxes means that you have the power and contrast voltages applied properly.  The fact that the potentiometer adjusted the visibility of the boxes means that it is working properly.

The fact that there are boxes on the display instead of text means that the LCD controller is not properly initialized as I mentioned before.  This could be due to bad wiring or the absence of the proper program code.

Here are several things to try:
- Rework your solder joints.
- Rewire the six lines between the Arduino and the LCD making sure to avoid digital pins 0 and 1.
- Make sure that your constructor data (the six numbers in parentheses) match your wiring.
- Make sure that LCD pin 5 is connected to GND.
- Make sure that loop() is empty for now.

23  Using Arduino / Displays / Re: LCD always gives black boxes.. on: August 14, 2014, 02:16:44 pm
Those are good points but they both can be taken care of after he gets the display functioning.

Many displays work acceptably with pin 3 grounded and his appears to be one of them.  The blocks are darker than optimal but the text should still be usable.  If the other row of blocks were visible I would say that he really needed a potentiometer.

Many displays work acceptably without a backlight and his appears to be one of them.  The blue displays with white letters are the ones that really need a backlight to be usable.

24  Using Arduino / Displays / Re: LCD always gives black boxes.. on: August 14, 2014, 02:04:56 pm
Your display is not being properly initialized.

Your photograph is not quite good enough to let us check your connections.  We need to be able to see both ends of every wire.

It would help if the focus were sharper as well.  Your soldering looks suspicious but I really can't tell.

Your program code, as simple as it is, is not correct either.  You do not want to write data that does not change in loop().  For now just remove everything between the brackets in loop().

You really should stay away from pin 1 (as well as pin 0) as it is used by the serial connection.  It is possible that your code is not being downloaded properly.


25  Using Arduino / Displays / Re: Clear Disaply but not position on: August 14, 2014, 11:16:46 am
I think you could do it simply by sending 80 'spaces' (0x20) to the display.  When you get done the address pointer should be right where it was when you started.

Follow the LCD Addressing link at if you want the background information on why this should work.

26  Using Arduino / Displays / Re: LCD,PC1602ARS, not displaying on: August 14, 2014, 09:09:07 am
However, there is no words being displayed except black boxes in both of the lines. I am using 5k potentiometer. I am not sure if this is the cause of the problem.

Most likely it is the cause.  Black boxes in both rows is typically caused by voltage on pin 3 that is too low.  This means that your potentiometer is either connected improperly or is defective.

The ends should go to pins 1 and 2 and the wiper should go to pin 3.  With the wiper at one end the display should be blank and at the other end you should see the two rows of boxes.  The correct position is typically near, but not at, the low end.

27  Using Arduino / Displays / Re: Sainsmart 16x2 LCD backlight not working on: August 13, 2014, 05:47:46 pm
82 ohm , 1/2 W gives you the required 4.2V backlight Voltage when connected to +5V

A better way to express this is: "82 ohm , 1/2 W gives you the required 50 mA backlight Current when connected to +5V"

Granted the LCD datasheets frequently list such a 4.2 V parameter but this is probably due to limited skills in 'technical English'  rather than it being an actual rating of the backlight LED.

What is actually happening is that the 82 ohm resistance is giving you the required ~50 mA forward current when connected to a +5 volt supply.  This in turn means that if you were to then measure the voltage across the backlight LED you would find that it is around 4.2 volts.

I bring this up because many people think that if you were to apply a 4.2 volt supply to this particular backlight LED that it would work properly - which isn't the case.

Once again, what is really happening is that when you limit the current (by whatever means) to the required 50 mA you will measure about 4.2 volts across the LED.

28  Using Arduino / Displays / Re: can a 20x4 lcd display using I2C have the backlight faded on: August 13, 2014, 08:18:59 am
A link to the datasheet for the display is necessary.

No.  A link to the datasheet for the I2C serial module is what is needed.

29  Using Arduino / Displays / Re: LCM1602C LCD + Arduino Uno R3 on: August 12, 2014, 08:14:14 pm
You really should have started a new thread since this one is more than two years old.

Typically when you vary the pot so that the VO voltage is higher than ideal the display will be very light (invisible) and when the voltage is lower than ideal the display will be very dark (maybe even just two rows of solid blocks).  

If the display actually requires a negative VO then the display will still be too light with 0 volts applied (with the pin grounded) so I don't think that is your problem.

My guess is that your potentiometer was defective or incorrectly connected.  

30  Using Arduino / Displays / Re: Sainsmart LCD 16x2 I2C alongside LCDSmartie for realtime temperature monitoring on: August 12, 2014, 08:02:26 pm
So what your saying is that LCDSmartie is actually sending those characters to the serial and the LCD is just printing them as its put out?

It certainly looks like that is what is happening.

The only reason I would question this is why.  The LCDsmartie program is designed to send information to LCDs using HD44780 type controllers.  Those controllers do not interpret the <CR> and <LF> control codes the way serial CRT do so, in my opinion, they never should be sent out by LCDsmartie.

So i have have to somehow modify how LCDSmartie outputs the data its sending to the Arduino?

That would be a possibility since the program appears to be open source.  Perhaps someone has already done this, have you checked all of the plug-ins?

Or am i able to rectify this with code on the arduino?

Yes.  I already mentioned one way, by programming two of the 'custom characters'.  I haven't been able to locate the previous thread where this was discussed.

You could also intercept the data between the and the LCD.write and filter out the unwanted codes.

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