why is my lcd screen not working arduino quotation

This stems from the fact that the LCD controller itself does not inherently support the function and in fact treats the ASCII codes for and as displayable characters instead of control codes.

The fact that the LiquidCrystal library inherits from Print class and thus permits the use of println() essentially makes things worse. Instead of barfing and spitting out an error message it just happily displays two unrelated characters on the screen and the uninitiated have no idea of the cause.

In my opinion the basic LiquidCrystal library should concentrate on implementing all of the capabilities of the LCD controller and no more. If people want a library that more closely emulates a CRT (or LCD) terminal that is fine, but I think it should be done in a different library.

The Adafruit tutorials are generally pretty good so without seeing your code and a picture of what that code produces, along with a picture of your setup we can"t determine what is wrong.

(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.

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.

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.

It"s 16x2, i"ve written some code to print out text but the only thing that appears is the top row filled with boxes and the bottom row showing nothing..

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. this is the product i bought: OSEPP - Multi Colored LED Assortment Set

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.

Unfortunately this is one of the "bodgie" shields for which the warning at the top of this forum applies. It is all right as long as you never make pin 10 an output and write it HIGH - which also means you must not include it in the descriptor.

Unfortunately this is one of the "bodgie" shields for which the warning at the top of this forum applies. It is all right as long as you never make pin 10 an output and write it HIGH - which also means you must not include it in the descriptor.

Posting a monstrously huge picture is not necessary and posting any picture without specifying the code that produced it is usually a waste of time and bandwidth.

Posting a monstrously huge picture is not necessary and posting any picture without specifying the code that produced it is usually a waste of time and bandwidth.

I have an lcd, and I am using it in a reaction timer project. What it is SUPPOSED to do is this: The led is off for a random amount of time. When it tuns on, the two players race to press their button as fast as they can. If a foul occurs, then a low tone is played and the lcd shows who fouled. If it is not a foul, the LCD shows who won and what their time was.

This is a game where there is an led and two buttons. as soon as the led lights up, the first player to push the button wins. If pushed before that, it is a foul.  If won, the lcd shows who

******************************************** These next two pins will only be on an lcd with a backlight. If there is no backlight, ignore these next 2 steps.

However, if you look at the video, you see that the LCD is not showing any characters. I don"t think it is the code, because it worked before. Am I applying too much voltage to it? The Pic shows that I am using 3.3v, but beforehand I was using 5v. Could that have damaged it?

For an I2C LCD display to work, the I2C address and the I2C backpack to LCD pin mapping must be correct. If the library default settings for either or both are not correct the LCD will not work. You can try to figure out the right pin mapping and use an I2C scanner to find the address, but if you install and use the hd44780 library that is done automatically by the library.

Install the hd44780 library. The hd44780 library is the best available for I2C LCDs. The library is available in the Library Manager. Go to Library Manager (in the IDE, Sketch, Include Libraries, Manage Libraries) and in the Topics dropdown choose Display and in the Filter your search box enter hd44780. Select and install the hd44780 library by Bill Perry.

The class that you want to use is the hd44780_I2Cexp class. There are examples to show how to use the library. The nice thing about the hd44780 library is that it will autodetect the I2C address and the I2C backpack to LCD pin mapping.

In the examples, there is a diagnostic sketch that will help us to help you if you still have trouble with the display. Run the diagnostic sketch and post the results.

Also there is the contrast adjustment, usually a small blue trimpot on the I2C expander backpack. If that is not adjusted properly the display will show nothing or just boxes.

SparkFun LCD page you liked to says the LCD you using is a 3V LCD display; HOWEVER, the datasheet shows it works from 2.7v to 5.5 - which means it really isn"t a 3v LCD.

Yes, as I say, that error has been simply copied by one "tutorial" after another, and incorporated into the I²C backpacks since it "sort of" works so people think it is OK. But it makes contrast setting more difficult and wastes half a milliamp. That may not seem much to worry about except that the LCD itself uses less than a milliamp and this would be significant it operating from a battery. The backlight of course draws 20 mA.

Not really. You will note if you tried both ways, that the contrast control is much more flexible connected this way. Instead of working only over a very narrow range at one end, it works over a much wider range - at both ends.

This is the equivalent of turning the potentiometer all the way to the ground end. In general, it will work and is OK to test if you are having problems (as you are), but generally does not provide the clearest display.

And indeed, if that is the display with no code running, the fact that you get only half a line of blocks demonstrates that the display is definitely faulty.

So the verdict is a dead display. I was a bit puzzled with your original picture and thought you had a 2004 display but of course, it is a 1602. On a 2004, the uninitialised display is "blocks" on the first and third line.

Pardon us when we ask for your actual code, but we always want to check what is in your IDE, not what the tutorial said because - it isn"t always the same.

Not sure what you are trying to articulate there, but if you are talking about the resistor in series with pin 15, that is another story. It is unnecessary with AFAIK, all of the currently available 1602 and 2004 modules since "R8" on the back of the module is "101" or 100 Ohms.

Well, it always used to be, but on the one shown in #11, "R7" is now 330 Ohms so the external resistor is even less necessary. I can"t quite see what "R8" is doing here, but it appears to add another 220 Ohms also. An extra resistor will not hurt things, it will just dim the backlight slightly and save some current.

In 4 bit mode, the host and the LCD must remain in nibble sync. If they lose nibble sync with each other, it will never recover so the LCD will start to see garbage commands.

So if the library is in 4 bit mode and you power cycle only the LCD, the host (arduino) and the LCD will not be in the same mode (LCD in 8 bit mode, host in 4 bit mode) and the LCD will see garbage commands.

In 8 bit mode, it is still possible to get glitches on the display, but since things are done byte at a time there is no nibble synchronization issue so any effects of noise should be short lived and future commands to the LCD should continue to work.

The question is then, does it only compile the modules required for a particular situation? Or to what extent does it incorporate code which is not needed?

Only compiling the modules needed isn"t the issue as the gcc compiler & linker have had the ability to be told to eliminate unused functions & data for quite some time and the Arduino IDE enables this.

The amount of dead wood code & data can vary depending on the version of gcc used and if/how virtual functions are used or if the code is assigned to an interrupt vector.

The ability to prune out unused functions does still exist.; however, the more recent versions of gcc have removed the ability to prune out unused virtual functions as the specific compiler & linker flags to deal with virtual functions (which were not enabled by the Arduino IDE), and linker code have now been removed from gcc.

IMO, this makes using virtual functions very expensive unless you really really need runtime binding which is not something needed or typically ever used in an embedded environment.

IMO, it relegates virtual functions to being a convenience capability that helps out from a s/w maintenance perspective, but there are other C++ techniques that can be used to offer the same capabilities that don"t suffer the dead wood code issue.

The ISR issue can be resolved with clever use of weak attributes, but the Arduino core & bundled libraries don"t do that so if an used Arduino supplied library, like say Wire is linked in, it will drag in all the code even if the sketch never references it.

The library manager LiquidCrystal_I2C library is a bare bones library that must have the i2c address configured and is hardcoded to a particular pin mapping between the PCF8574 and the LCD. It doesn"t work with several of the software i2c libraries.

fm"s newLiquidCrystal compiles all the i/o classes and links them in regardless of them being used and do to poor coding in other Arduino library code referenced, there is few k of unused code that can be dragged in that is unused and unrelated to the i/o class being used. This is not related to the virtual function issue. This is mainly an issue when not using an i2c based device as the Wire library code and data is always linked in regardless of whether it is used by the sketch.

hd44780 with the hd44780_I2C i/o class for an application like a PCF8574 based backpack does end up dragging in around 1.5k or so of uneeded code from a combination of the virtual function issue and the auto chip detect code to determine PCF8574 of MCP23008 and then the MCP23008 support code.

I"m fully aware of these issues and do have plans to resolve this by refactoring the code get around the virtual function issue so that only code that is actually used/referenced is linked in.

I think this could make things even easier for users (especially non English speaking users) since there would be, less documentation to read, no confusion over i/o classes and the code could be even smaller than a refactored hd44780_I2Cexp i/o class as there would be no code to detect and handle other chips

Posting a monstrously huge picture is not necessary and posting any picture without specifying the code that produced it is usually a waste of time and bandwidth.

The simplest way to test the display does not involve cursor positioning at all. Just send 80 printable ASCII characters to the display and all of the character positions should be filled.

That actually just indicates an uninitialised display, meaning the HD44780 (clone) has not responded to the initialisation command, and is not generating the strobes for the second line.

The question then becomes, from where do those "noise" characters come, as they clearly do not correspond to the working code? I think the answer is that the LCD is seeing some activity on its inputs, but has not received the proper initialisation sequence.

That actually just indicates an uninitialised display, meaning the HD44780 (clone) has not responded to the initialisation command, and is not generating the strobes for the second line.

That actually just indicates an uninitialised display, meaning the HD44780 (clone) has not responded to the initialisation command, and is not generating the strobes for the second line.

Actually a single row of blocks (or two out of four rows) indicates an improperly initialized display controller. Typically the controller has not been initialized by your code so it retains the default initialization that should occur at power-up. This is for a single line display (a display using a single line of memory, not necessarily a display using a single row of characters). These single line displays use a a different multiplexing scheme with a different duty cycle, hence the dark row of blocks. Also the addressing scheme is different when you get beyond the first 40 characters.

As far as we are concerned there is no difference between an uninitialized and an improperly initialized display but the term improperly initialized is the correct one.

This stems from the fact that the LCD controller itself does not inherently support the function and in fact treats the ASCII codes for and as displayable characters instead of control codes.

The fact that the LiquidCrystal library inherits from Print class and thus permits the use of println() essentially makes things worse. Instead of barfing and spitting out an error message it just happily displays two unrelated characters on the screen and the uninitiated have no idea of the cause.

In my opinion the basic LiquidCrystal library should concentrate on implementing all of the capabilities of the LCD controller and no more. If people want a library that more closely emulates a CRT (or LCD) terminal that is fine, but I think it should be done in a different library.

Dealing with these LCDs is really very interesting. Like so many other things they are really quite straightforward once you understand them but they seem really complex when you don"t. What makes them more challenging is that in some respects they require you to meticulously follow the data sheet and in other respects they are quite tolerant of deviations.

What really messes people up is that the various clones of the original Hitachi design seem to be tolerant of different deviations. So experimenter "A" comes up with some not exactly correct code that works with his LCD and passes on this "working" code. Experimenter "B", with a different brand LCD, tries it and when it doesn"t work for him he comes up with another version of not exactly correct code that works with his LCD and passes that code on....

Sticking to the original Hitachi recommendations is the best bet, but those recommendations are sometimes hard to decipher due to translation and/or editorial errors.

Any advice would be gratefully recieved as i think i am just missing something silly, and if i have missed information you need i am sorry, and please do let me know

We sell tons of lovely character LCDs for use with Arduino, they are extremely common and a fast way to have your project show status messages. This tutorial will show how you can easily connect a character LCD, either 16x2 or 20x4.

i"m sure all my connections are correct, the display works according to the program but it is very unclear even after adjusting the 10k pot..im not sure what the problem is please help me out..some extra info:

The clear blunder is not comprehending what the "Vin" or "RAW" terminal is. The regulator on the Arduino UNO/ Nano/ Pro Mini/ Mega2560/ Leonardo/ Pro Micro has very little heatsink, so will not pass very much current (depending on the input voltage and thus, how much voltage it has to drop) before it overheats and (hopefully reversibly) shuts down. It is essentially little more than a novelty provided in the very beginning of the Arduino project when "9V" power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.

Nowadays, 5 V regulated switchmode packs are arguably the most readily available in the form of "Phone chargers" and switchmode "buck" regulators to regulate down from 12 V or other available voltages are cheap on eBay so these can be fed into the USB connector or (more appropriately) 5 V pin to provide adequate power for most applications. Unfortunately, many tutorials or "instructables" are seriously outdated or misleading and have not been updated to reflect the contemporary situation.

BJHenry has a valid point. On the Mega SDA is pin 20, SCL is pin 21. Or on the header where pins 8-13 are the order is 12, 13, Ground, Aref, SDA, SCL. SCL nearest to the USB connector.

Thanks! This indeed ended the "lag". However, plugging to VO pin directly to GND is way to much backlight, so I must restrict it, which I"ll probably do with a 390R or similar.

You suffer from a couple of very common matters of confusion here. The backlight is the LED powered by the 420 Ohm resistor. You can if you wish, switch it on and off to conserve power by connecting it to an Arduino pin and you could even dim it using PWM, but generally you only need a choice of three brightness levels; fully on, dim for night use, or off, and these can be set using resistors. The LCD board usually contains a 100 Ohm ("101") resistor at R8 to set the LED current which allows it to be directly controlled by an Arduino pin.

"Vo" sets the contrast of the display. This requires a voltage of between 4.5 and 5 V negative to Vcc for the common display materials (significantly greater however, for those designed to work is extreme cold). When the original chip was designed many years ago, one "test" circuit was published with a potentiometer to set the voltage and in a fascinating blunder, engineers ignored the other design information and ever since imagine a potentiometer is necessary. In fact, what is required is a resistor, fixed or variable, from Vo to ground. Since the chain of resistors internal to the display board total 11k, (five times 2k2) a resistor of up to 1k to ground is just about right.

In the Arduino IDE terminology, it is the source code that is called a "sketch". Asking for your "sketch" is asking for you to post your code using the "code" ( icon at the top of the "Post Reply" window) macro.

No, the mystery is why it ever functioned if you drive the contrast chain with PWM. What happens is a complex interference between the PWM waveform and the multiplexing frequency of the LCD driver. Whether it is visible at all is a fluke.

If you do not wish to include a variable resistor, just use a 390 or 470 Ohm resistor between Vo and ground. Try one and the other, and use what looks best. Note however that if your Vcc varies, so will your contrast, no matter how you connect it. Unfortunately, every so often, someone confuses PWM with a variable voltage and if they are really unlucky, it actually works and they write it up on "Instructables" or some similar site to entrap newbies.

I put it to clear a certain part of the lcd where the millisecond counter is. It never cleared. When i replaced the lcd.print(""); with lcd.print("."); it displayed an period where I wanted the nothing.

Newhaven 4x40 character Liquid Crystal Display shows characters with dark pixels on a bright white background when powered on. This transflective LCD Display is visible with ambient light or a backlight while offering a wide operating temperature...

And the bottom 2 lines do not light up at all, top two are mostly readable but cut in and out. Not turn on and off, just cut in and out. PS, this application is with an existing control system that required several pins to be swapped around, when first plugged in the DB pins were swapped, so 1 and 2 were 2 and 1. 3 and 4 were 4 and 3 etc.