liquid crystal arduino library for the dfrobot i2c lcd displays made in china

The second step is to add the libraries to your arduino ide, to do that you go to sketch-> include library -> add zip library then find it in files. If it works, you should get a message saying it worked.

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It is the reimplementation of the standard Arduino LCD library, configured to work with parallel HD44780 compatible LCDs, and interfaced via a Chinese PCF8574 I2C serial extender.

inttypes.h: Integer type conversions. This header file includes the exact-width integer definitions and extends them with additional facilities provided by the implementation.

Some of listed functions come out of Arduino LCD API 1.0, some of them are specific for this library. It is possible to use functions from the system library Print, which is extended by the LiquidCrystal_I2C.

Note, however, that resetting the Arduino does not reset the LCD, so we cannot assume that it is in that state when a sketch starts (and the constructor is called).

Initializes the display with values put to the constructor, clears the screen, and puts cursor to the upper left corner of the screen, i.e., to the home position 0,0. It is a wrapper function for function begin() with forgoing initialization of Wire library.

The functions sets the cursor to the start column and row after clearing, i.e., after calling without parameters to the home position (0, 0), or after calling with parameters to the starts of cleared row segment.

Prints text or number to the LCD. It is inhereted function from the parent system one. The function is overloaded and acts according the data type of the input data to be printed.

Scrolls the display text to the left without changing the RAM. The function scrolls entire 40 character buffer. If you print 40 characters to a row and start scrolling, you get continuous moving banner in a row especially on 1602 LCDs.

Scrolls the display text to the right without changing the RAM. The function scrolls entire 40 character buffer. If you print 40 characters to a row and start scrolling, you get continuous moving banner in a row especially on 1602 LCDs.

The bar graph is composed of solid, full rectangle characters eventually except final character with reduced vertical pipes. Value of the bar graph is displayed as equivalent number of pipes in the graph segment.

pixel_col_end: Displayed value in pipes (horizontal dots) counting from 0 to number of pipes of the graph segment. A sketch should calculate the number of segment pipes in order to map an application value to displayed value.

The bar graph is composed of solid, full rectangle characters eventually except final character with reduced horizontal dashes. Value of the bargraph is displayed as equivalent number of dashes in the graph segment.

pixel_col_end: Displayed value in dashes (vertical dots) countingfrom 0 tonumber of dashes of the graph segment. A sketch should calculate the number of segment dashes in order to map an application value to displayed value.

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I2C_LCD is an easy-to-use display module, It can make display easier. Using it can reduce the difficulty of make, so that makers can focus on the core of the work.

We developed the Arduino library for I2C_LCD, user just need a few lines of the code can achieve complex graphics and text display features. It can replace the serial monitor of Arduino in some place, you can get running informations without a computer.

More than that, we also develop the dedicated picture data convert software (bitmap converter)now is available to support PC platform of windows, Linux, Mac OS. Through the bitmap convert software you can get your favorite picture displayed on I2C_LCD, without the need for complex programming.

Select the board: Click Tools > Board > "Arduino Duemilanove or Diecimila"(Seeeduino V3.0 Or early version), "Arduino Uno"(Seeeduino Lotus or Seeeduino V4.0).

I"d try disconnecting the SDA & SCL wires and power the display with 5V. Then measure the voltage on its SDA and SCL pins. It will probably be 5V if the display has pullup resistors.

Then I"d try a 1K resistor between SDA and 3.3V. Worst case, that will feed 1.7mA into the 3.3V supply, which is safe since Teensy uses more than 1.7mA on 3.3V power. But a far more likely case is you"ll get some voltage like 3.5V. The actual voltage will depend on whatever resistors are on that display. If you measure 3.6V or less, then it should be safe to connect to Teensy. Just make sure than 1K resistor stays in place, so the pulled-up voltage is 3.6V or less.

I recently acquired, via eBay, a 40X4 HD44780 based LCD screen that has a daughter-board on the back that provides an I2C interface, labled “LCD2004“. This permits interfacing with only two wires (SDA/SCL) plus ground and 5-volts. This particular board is sold by a Chinese company,  SainSmart.com. SainSmart provides its own version of the Arduino LiquidCrystal library and some example code. Unfortunately, both the library are for the old version of the Arduino IDE and will not compile with the current Arduino 1.0 version.

To get the I2C display to work I did some reverse engineering. The LCD2004 board utilized the PCF8574 I/O expander. This nifty little chip provides eight bits of parallel I/O addressable by a I2C bus address – 0x00 to 0x27. SainSmart tied all address leads to Vcc, so the LCD2004 board’s I2C address is permanently fixed at hex 27. This is rather limiting since no additional LCD2004s can be added to the bus. Anyway, you simply address the board and write an eight bit value which is then presented on the output pins of the PCF8574, which, in this case, are connected to the HD44780 based LCD screen.

After some reverse engineering to determine which PCF8574 pins were connected to which LCD pins, I was able to use  F Malpartida’s NewLiquidCrystal library to write a functional test program. The unit works quite nicely and my code and schematic can be obtained in my BitBucket Repository.

The SainSmart LCD2004 board is identical to one offered by YwRobot and SainSmart’s provided example code is even marked with Ywrobot. Possibly SainSmart merely markets the Ywrobot board under their name, or possibly they cloned it. Furthermore, both Ywrobot may have obtained its design from DFrobot. DFRobot may have been the original board designer given their more professional approach of decent documentation, but given China’s disregard for intellectual property rights, who knows for sure? Also, DFRobot has and active forum with timely responses by their engineers, and a wiki, which is another plus for their professionalism. DFRobot’s board and SainSmart’s significantly differ, physically, so if SainSmart copied DFRobot, it was only from their schematic and not the board design.

A more versatile I2C LCD board would be to use the design offered by F Malpartida. Her I2CLCDextraIO board allows you to define a unique address for each LCD, permitting a multi-display configuration with all controlled over one I2C bus. Her designs are freely available in her BitBucket repository if you’d like to make your own board. You can also buy her bare board or assembled unit from ElectroFUN.

The library allows to control I2C displays with functions extremely similar to LiquidCrystal library. THIS LIBRARY MIGHT NOT BE COMPATIBLE WITH EXISTING SKETCHES.

Holding the serial module with the I2C interface at the left hand end, there are 16 pins at the lower edge. The first of these is ground, and the second of these is +5v. Another option is to use the lower two pins on the I2C interface for power, but I found it more convenient to use the pins as described above.

I2C interface. On the serial module, the top pin is SCL (clock) and it goes to the Arduino A5. The second pin down is SDA (data) and it goes to the Arduino A4.

LCD print interface. There are 6 connections between the serial module and the LCD Keypad shield, all of them between pins with no labels. I will identify them on the LCD module by counting from Right to Left, with the first pin as 1. There are 2 blocks of 8, so they go from 1 to 16. I identify them on the I2C serial module by counting from Left to Right, there are also 16 of these. In addition I give each wire a label, which is the equivalent pin on the Arduino that is normally associated with that function, in the case of a direct connection without the serial module.

Keypad interface: This uses a single wire from the LCD module pin on the lower side labelled "A0", to pin A0 on the Arduino. At least that was pretty easy!