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Topic: New LiquidCrystal library - LCD library (Read 68693 times) previous topic - next topic


Apr 04, 2012, 07:16 pm Last Edit: Apr 04, 2012, 07:46 pm by bperrybap Reason: 1
I want to stress DO NOT use the backlight control on the DFRrobot-007 LCD keypad shield.
That board as a hardware design issue and if you set D10 to high,
it creates a short from D10 to ground.
See this thread for details:

In the mean time I'll go off and test the latest zip file ( LiquidCrystal_v1.2.0.zip) with Arduino 1.0.
I've not seen the issue you are seeing, but lately I've only been running
the pre-release version of the library. I'll go try a bone stock Arduino 1.0
with the library from the latest zip and see if there is an issue.

--- bill

I have downloaded LiquidCrystal_v1.2.0.zip ( https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads/LiquidCrystal_v1.2.0.zip )
and used it to replace the LiquidCrystal library in bone stock download of the Arduino 1.0 IDE.
All the included example sketches compile without issue.

In looking closer at the example sketch that got the errors, (should have seen this earlier),
that sketch will not compile with the standard Arduino 1.0
It is a pre 1.0 sketch.
0 (zero) is an ambiguous type in C.
The Arduino Print class use C++ overloading and the Arduino team did not include enough functions
in Arduino 1.0 to catch zero. This is an Arduino library issue. It is easily fixed by either modifying the print class
(which is what Teensyduino has done for the teensy boards) or you can modify your sketch.

To modify your sketch you must type case zero.
So things like:
Code: [Select]
need to be:
Code: [Select]
Code: [Select]

All the examples that come with the new library like Hello_World_4bit.ino have this modification
already in them.

--- bill


@bperrybap - thank you for your timely warning in thread:

However please note at Reply #10 to that thread, that I posted a simple fix to the cct error you point to inherent in the DFRrobot-007 LCD keypad shield.

Hopefully DFRobot themselves will point to this fix themselves from within their support documentation.

And with regard to the "Custom Characters" sketch compile error, I much appreciate your effort in explaining that - the 0 (zero) as an ambiguous type in C not being caught in the Arduino Print class - is an inherent error of the IDE, and not the New LiquidCrystal library.

However as a learning exercise I continued to try and see whether you advice could 'fix' the original error through replacing the offending line of code with your example:
Code: [Select]

but am still encountering a compilation error as follows:
CustomCharacter.cpp: In function 'void setup()':
CustomCharacter:114: error: call of overloaded 'write(char)' is ambiguous
/Applications/Arduino.app/Contents/Resources/Java/libraries/LiquidCrystal/LCD.h:479: note: candidates are: virtual size_t LCD::write(uint8_t)
/Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/cores/arduino/Print.h:49: note:                 size_t Print::write(const char*)

If I alter the offending code to:
Code: [Select]

the compile is successful but the sketch does not run when uploaded.


I'm so sorry on both counts.

write() wants an unsigned char. Shame on me. I should have looked to make sure and then tested it.

The proper code would be:

Code: [Select]
xxx.write((uint8_t) 0);
xxx.print((char) 0);

moral of the story: print "char"s and write "bytes".

I tested your exact example sketch after changing the
lcd.write(0); to lcd.write((uint8_t) 0);

It worked on my lcd shield. (mine is same pinout as the DFR)

I'm not sure what the issue is about not running.
Which version of the library are you using? The tip of the tree?
with backlight control?
Are you using the backlight control?
(in RC5 library will use it during begin() if it is in the constructor)
Was the shield working ok with backlight control after the mod?

--- bill



Code: [Select]
  lcd.write((uint8_t) 0);

works perfectly on my DFRrobot-007 LCD keypad shield. Thank you.

I am indeed using  back light control now that the cct. error has been corrected. A working code example involving back light control is:
Code: [Select]
//Sample using LiquidCrystal library
#include <LiquidCrystal.h>


This program will test the LCD panel and the buttons of
the DFRobot LCD Keypad Shield for Arduino
Product code : RB-Dfr-07

Note cct error identified by Arduino forum discussion at:
which advises insertion of a Germanium 1n34a or a Schotky 1N5819
diode between pin 10 and the base of Q1 (K to pin 10).

sample code originally by Mark Bramwell, July 2010
modifications by Dion Weston, March 2012


// select the pins used on the LCD panel
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

// define some values used by the panel and buttons
int backLight   = 10;    // LCD Panel Backlight LED connected to digital pin 10
int lightLevel  = 255;   // Initialise light full on
int lcd_key     = 0;
int adc_key_in  = 0;
#define btnRIGHT  0
#define btnUP     1
#define btnDOWN   2
#define btnLEFT   3
#define btnSELECT 4
#define btnNONE   5

// read the buttons
int read_LCD_buttons()
adc_key_in = analogRead(0);      // read the value from the sensor
// my [Mark Bramwell's] buttons when read are centered at these values: 0, 144, 329, 504, 741
// we add approx 50 to those values and check to see if we are close
if (adc_key_in > 1000) return btnNONE; // We make this the 1st option for speed reasons since it will be the most likely result
if (adc_key_in < 50)   return btnRIGHT; 
if (adc_key_in < 195)  return btnUP;
if (adc_key_in < 380)  return btnDOWN;
if (adc_key_in < 555)  return btnLEFT;
if (adc_key_in < 790)  return btnSELECT;   
return btnNONE;  // when all others fail, return this...

void setup()
lcd.begin(16, 2);              // start the LCD library
lcd.setCursor(0,0);            // move cursor to beginning of line "0"
lcd.print("Backlight adjust"); // print a simple message
// Serial.begin(9600);            // initialise serial communications:


void loop()
analogWrite(backLight, lightLevel);
lcd.setCursor(13,1);            // move to position 13 on the second line

lcd.setCursor(0,1);            // move to the beginning of the second line
lcd_key = read_LCD_buttons();  // read the buttons

switch (lcd_key)               // depending on which button was pushed, we perform an action
   case btnRIGHT:
     lcd.print("LED On          ");
     lightLevel = 255;
   case btnLEFT:
     lcd.print("LED Off         ");
     lightLevel = 1;
   case btnUP:
     lcd.print("LED Fade Up     ");
     if (lightLevel < 255) lightLevel += 1;
   case btnDOWN:
     lcd.print("LED Fade Down   ");
     if (lightLevel > 1) lightLevel -= 1;
   case btnSELECT:
     lcd.print("Select          ");
     case btnNONE:
     lcd.print("                ");



Hi folks,

I have just published release 1.2.1 of the New LiquidCrystal library. So what do we have on this release:
- improved backlight control
- enhanced support for shift register control: 2 wire, 3 wire and 1 wire (preview)
- if it was fast, now is even faster: for the shift register configurations, in some cases 5.55 times faster than the standard (courtesy of bperrybap)
- reorganized and cleaned up a bit
- gone through intensive testing

Check it out @ https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home
Download it @ https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads

Within the coming days I will be updating the wiki to improve the schematic section, it will also have for each library a description as to how to configure it.

All this with the contribution of:
- bperrybap
- piccaso


Apr 05, 2012, 10:10 pm Last Edit: Apr 05, 2012, 10:16 pm by bperrybap Reason: 1
The latest library also works on Chipkit.
(Has been tested on the Uno32)
So you can use the same LCD interfaces and backlight control on the pic32 based
Arduino boards using mpide.

There are also some new examples.
LCDiSpeed can be used to show the speed of the LCD interface.
It will tell you how fast a single character and how fast the full
display can be updated.
(See the sketch for details)

--- bill


Apr 06, 2012, 11:35 am Last Edit: Apr 06, 2012, 11:39 am by dweston Reason: 1
Thanks again fm, bperrybap and piccaso


For what it may be worth I obtained the following speeds using a DFRrobot-007 LCD keypad shield coupled to an Arduino Duemilanove using the LCDiSpeed sketch:

(ByteXfer) 85uS
Frame/Sec (FPS) 345.78
Frame Time (Ftime) 2.89mS


Am I right in assuming the new Liquidcrystal library doesn't support event handling as in: addEventListener in the old version?
Also, prior to writing to LCD (write/print), port pins are not set/reset so as to allow usage of pins by other device (multiplexing)?


All these features would have to be built around it. See the library as a generic LCD driver, adding a listener in the application and callbacks is a trivial task. Arbitrating pin usage is also trivial and the library doesn't constrain you, further more this is application dependent, not the responsibility of the driver. Why do you want to penalise users if they don't use muxing, for example?



My apologies, I posted out of context...

In agreement in relation to the first point, it doesn't need it, as to multiplexing, the driver already ensures the pins are set prior to writing therefore it already supports multiplexing...

I incorrectly assumed the new driver did do pin assignment before writing as a sketch (using shared/mulitplexed pins), that worked with the old library did not work on the new... I now need to determine the real problem...


No apologies needed at all.

As with all good software, you need to arbitrate the usage of shared resources. It is not good practice at all to assume that when you allocate the resources to a particular device/variable, later on someone else has changed it and hence you write it back just in case. Since you are in control of the application, it is up to the application to share a resource and hence to manage it. There are several ways you can do that, for example a software "mux" (a monitor) that reconfigures the IOs before executing a transaction over the share resource.

This is more evident when you work with concurrent systems or multi-threaded environments.


Thanks for the update!

When using a shift register in 2-wire mode, is it possible to control the backlight with bit 1 of the shift register?  My backlight is hooked up according to this schematic.



yes, you can.
While the SR interface code supports both 2 wire and 3 wire modes,
currently only the SR2W interface code has support for backlight control.
From your link to the schematic it looks like you are using a unlatched SR register like the 74LS164 vs using
a 74HC595 in a "non latched" mode (you can see my version of that just a bit lower on the same page
you linked to)

If you look in the header file LiquidCrystal_SR2W.h you will see a detailed explanation
along with ASCII art of how to hook up either SR register for backlight control using bit 1 of the SR.
If you are looking for a simpler anti-flicker circuit, I also included a diagram for simple backlight control circuit that
also removes the flicker. It uses a FET but is simpler
and more power efficient than the one in the schematic you linked to.

The ascii art in the header file needs a bit of an update.
I'm now using 4.7k resistors for all resistors except the current limiting resistor
and the diode is a 1N4148.

--- bill


Hi Bill
Thanks for the quick reply!  Indeed I am using a 74HC595 in 'non-latching' mode.  Thanks for that FPS sketch, it's really neat.  I didn't know you could use if and elif statements for defined objects like that, super cool.

Anyhoo, I made a harness at work that has a 2x16 connector on one end for the LCD and the SR and everything else soldering in the middle, so I'd just have 4 wires going to the controller on the other end.  I used the backlight anti-flicker with the series diodes and transistor but it doesn't seem to be working.  Too bad I heat shrunk it all up before testing...d'oh!  I can just snip off the LCD part though and try out your FET version.

You mention using a 1n4148, but I don't see it in your ASCII diagram:
Code: [Select]
// (LCD BL anode)---[ resistor ]---(vcc)
// (LCD BL cathode)-------------------------------+
//                                                |
//                                                D
//                                                |
// (BL input)----[ 4.7k Resistor ]----+-------G-|-<  (2N7000 FET)
//                                    |           |
//                          (0.1uf)   =           S
//                                    |           |
//                                  (gnd)        (gnd)

Would it go between the 4.7k/0.1uF and the gate of the FET (cathode towards the FET)?


Jun 06, 2012, 07:03 am Last Edit: Jun 06, 2012, 07:07 am by bperrybap Reason: 1
There is quite a bit of "magic" that can be done using the C pre-processor.

Sorry for the confusion. The diode isn't part of the backlight circuit.
The backlight circuit is as shown in the backlight ascii art.
If you look above the backlight ascii art in the header file you will see the ascii art for the 595 circuit.
That includes a diode but it didn't say or recommend one. That is where I'm using a 1n4148.

--- bill

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