pcf8574 i2c lcd module quotation
16×2 LCD is an alphanumeric display that can show up to 32 characters on a single screen. You can display more characters by scrolling the texts one by one. We have already seen how to connect LCD Display directly with the Arduino using 4bit and 8bit modes in our previous tutorial. But those two modes will utilize many numbers of GPIO Pins of our Arduino and we would have to end up with less number of pins for other sensors and actuators.
To overcome this problem we use LCD I2C backpack with our LCD. This I2C Backpack uses PCF8574 Remote 8 bit I/O Expander. It translates the data received from the I2C Bus into Parallel data that is needed for the LCD Display.
Inter-integrated Circuit (in short I2C) is a two-wire short distance communication protocol. You can use multiple slave devices in the same two wires with one or more master controllers. You may wonder how does the master identifies which slave does the data to be sent. In I2C the external devices have an I2C address for different external devices like LCD Backpack, OLED Display, etc. By using the address the data is sent to the specific device connected on the same I2C Bus.
The message is broken into two frames and sent serially via the I2C Bus. The first frame contains the address, once the address matches with any device on I2C bus, that device will send an acknowledge signal to the master. After receiving the acknowledgment from the slave the data bits are sent. By this method an I2C bus works.
There are totally 16 pins in an LCD Display. You can use directly all the pins in 8-bit mode with Arduino or 12 pins using 4-bit mode. In this tutorial, we use the I2C module for LCD and multiplex it into just 4 pins. This pin details might not be useful while using I2C Method but this is the actual pin details of all the pins in LCD Display.
RS – Register select. Specify what we are sending Command or Data. Sets to 0 for Command mode like setCursor, LCD Clear, TurnOFF LCD. Set 1 for data mode like sending Data/Characters.
First, we need to find the address of our I2C LCD Backpack. For that, we will be using I2C Scanner code to display the address in the serial monitor. Upload the following code, then note down the I2C address from the serial monitor.#include
In my case, it is 0x27. Node down the address displayed for you. Mostly it will be 0x27 only. In case you have another I2C device connected on the same bus it will show that address too.
Download .zip LiquidCrystal_I2C library by Frank de Brabander from hereand Install it in IDE by navigating Sketch>Include Library>Add .zip library and choose the downloaded LiquidCrystal_I2C.zip library file.
Now the LCD I2C library is installed. We need to define and initialize the library using its associated functions. The steps is as follows. Or you can copy the code given below to print Hello World example.
Set the address that we copied from I2C Scanner code. The address I got is 0x27 so I replaced it to 0x27 in the following lineLiquidCrystal_I2C lcd(0x27, 16, 2);
In the above code, we have created an LCD object for ‘LiquidCrystal_I2C’. So you can use directly use the regular LCD functions to work with I2C like lcd.begin(), lcd.print(“”), etc.
To print a string we use lcd.print() function with string in its parameters. This prints ‘Factory’ string in the 1st row and ‘Forward’ in the 2nd row.
This function sets the cursor on 7th column and 2nd row. Printing the string will gets displayed from this location on LCD.lcd.setCursor(6,1); // Sets cursor column and row position
By Using lcd.blink() function we can make the cursor blinking on LCD. To turn off the blinking cursor we use lcd.noBlink() function.lcd.blink(); //Blinking cursor
Use lcd.cursor() function for printing an underscore symbol. It is also used for notifying users to enter some values.lcd.cursor(); // Prints an underscore symbol
I2C Adapter Board fits right on the back of standard LC character display modules with 1 x Hitachi HD44780 or compatible display controller. The on-board PCF8574 or PCF8574A 8-bit I/O expander encodes the signals for the 4 data bits, the read/write select, register select, the enable signal, and the backlight-ON signal.
The supported I2C addresses depend on the version of the expander IC – please refer to the manufacturer PDF or find plenty of information online (for example Arduino forum).
Additional circuit design information: The I2C bus on development boards like the Arduino series of boards doesn’t have the necessary pull-up resistors already installed. To make the I2C connection happen, you will need pull-up resistors from VDD to SDA and SCL. The value of these resistors is not critical, as long as the connections are short and the data rate low. For just 1 or 2 displays on 5V logic level is a value of 2k to 20k a good choice.
This LCD I2C interface adapter can be added to a 16 x 2 or 20 x 4 character LCD display with a standard parallel interface to make it I2C compatible. It can also be repurposed for other I2C to parallel tasks.
By default, the industry standard HD44780 compatible 16 x 2 and 20 x 4 character LCD displays require 4 or 8 parallel data lines to drive them along with a couple of pins for chip select and chip enable. This consumes a lot of pins on the MCU. This adapter board reduces the data pin requirements to only 2 pins which can also be shared with other I2C devices.
The backlight can be controlled ON/OFF, but the intensity is not directly controllable though the I2C interface. Some modules have a jumper on the board that supplies Vcc power to the backlight. That jumper can be removed and a voltage applied to the header pin nearest the ‘LED’ markings on the board to provide power to the backlight separately. Note: Some modules do not have this header / jumper installed, instead the solder pads have a trace connecting them. It is possible to cut the trace between the pads and add header pins if desired.
The PCF8574 is a generic I2C to 8-bit I/O device and the module can be repurposed for other uses besides driving LCD modules. Max I2C clock frequency is 100kHz which makes it most suited to lower speed applications.
VCC = Connect to 5V. This can come from the MCU or be a separate power supply. Some LCD may operate at 3.3V and this module can also operate at 3.3V
The pin-out of the header which is soldered to the LCD follows for reference, but in general you don’t need to worry about it as the I2C interface board and software library takes care of this interface unless you are adapting the module for another use. These pins are listed starting at the I2C header end of the board.
To use the adapter with an LCD, you will need to insert the 16-pin header into the 16 solder pad holes on the back of the LCD and solder them in place on the front side. The pins are long and can be cut off before or after soldering.
Soldering the module on is easy to do, but if you already have other pins in those holes, they will need to be removed first before this board can be added. The picture below shows the adapter mounted to the back of an LCD2004 4 x 20 character LCD.
This is the same module used on our I2C compatible LCD displays we sell and is well supported using the LiquidCrystal_I2C.h and similar libraries. For using the board with software, you can check out one of the LCDs below that already have this module installed.
The PCF8574 itself is a general purpose 8-bit I/O expander for the I2C bus. The reverse engineered schematics are provided here mainly for those who may want to adapt the module to other applications. The I2C bus on this module is limited to a 100kHz clock frequency.
This article includes everything you need to know about using acharacter I2C LCD with Arduino. I have included a wiring diagram and many example codes to help you get started.
In the second half, I will go into more detail on how to display custom characters and how you can use the other functions of the LiquidCrystal_I2C library.
Once you know how to display text and numbers on the LCD, I suggest you take a look at the articles below. In these tutorials, you will learn how to measure and display sensor data on the LCD.
Each rectangle is made up of a grid of 5×8 pixels. Later in this tutorial, I will show you how you can control the individual pixels to display custom characters on the LCD.
They all use the same HD44780 Hitachi LCD controller, so you can easily swap them. You will only need to change the size specifications in your Arduino code.
The 16×2 and 20×4 datasheets include the dimensions of the LCD and you can find more information about the Hitachi LCD driver in the HD44780 datasheet.
After you have wired up the LCD, you will need to adjust the contrast of the display. On the I2C module, you will find a potentiometer that you can turn with a small screwdriver.
The LiquidCrystal_I2C library works in combination with the Wire.h library which allows you to communicate with I2C devices. This library comes pre-installed with the Arduino IDE.
*When using the latest version of the LiquidCrystal_I2C library it is no longer needed to include the wire.h library in your sketch. The other library imports wire.h automatically.
Note that counting starts at 0 and the first argument specifies the column. So lcd.setCursor(2,1) sets the cursor on the third column and the second row.
Next the string ‘Hello World!’ is printed with lcd.print("Hello World!"). Note that you need to place quotation marks (” “) around the text since we are printing a text string.
The example sketch above shows you the basics of displaying text on the LCD. Now we will take a look at the other functions of the LiquidCrystal_I2C library.
This function turns on automatic scrolling of the LCD. This causes each character output to the display to push previous characters over by one space.
I would love to know what projects you plan on building (or have already built) with these LCDs. If you have any questions, suggestions or if you think that things are missing in this tutorial, please leave a comment down below.
pulsarus, If you are out of ideas, and are unable to determine the pin wiring of your i2c chip to the hd44780 interface, attached is a sketch I wrote that will try to figure it all out by guessing. It will locate the i2c chip’s address then try...
A regular LCD requires a lot of wires (parallel interface) to be connected with a Microcontroller.The Serial LCD backpack built on PCF8574 IC uses the I2C bus to convert the parallel interface to a serial one.This needs only2 wires SDA & SCL , apart from the power connections.
The blue preset is to adjust the contrast of the LCD. The black jumper on the left is to enable the Backlight of LCD. The I2C device has a HEX address by which a microcontroller can communicate with it.This is set by the 3 bits A0,A1 ,A2 .If no jumper is present , it is HIGH & a jumper means LOW. By default all the 3 jumpers are open . ie., A0,A1 A2 all are 1s.
The I2C bus has 2 bidirectional active wires SDA & SCL .They are joined to positive supply through a pull up resistor of 4k7.When the bus is idle both lines are pulled high.
lcd.setBacklightPin(HIGH); makes the P3 pin go High, which turns on the NPN transistor.This provides GND to the LED pin of LCD As the other LED pin is already connected to Vcc through the jumper , the LCD backlight glows.
These modules are currently supplied with a default I2C address of either 0x27 or 0x3F. To determine which version you have check the black I2C adaptor board on the underside of the module. If there a 3 sets of pads labelled A0, A1, & A2 then the default address will be 0x3F. If there are no pads the default address will be 0x27.
Serial I2C LCD display adapter converts parallel based 16 x 2 character LCD display into a serial i2C LCD that can be controlled through just 2 wires. Adapter uses PCF8574 chip that serves as I/O expander that communicates with Arduino or any other microcontroller by using I2C protocol. A total of 8 LCD displays can be connected to the same two wire I2C bus with each board having a different address. The default i2C address is 0X27 and may be changed to any of the following 0X20~0X27 via soldering A0 A1 A2 pins.
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.
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.
True to its name, these LCDs are ideal for displaying text/characters only. A 16×2 character LCD, for example, has an LED backlight and can display 32 ASCII characters in two rows with 16 characters on each row.
If you plan to add a simple readable interface in your next project. alphanumeric LCD may be the most preferred one due to various factors such as low cost, easily programmable, having no limitation of displaying special & even custom characters.
But to use it directly with a microcontroller, you would need atleast 6 pins – RS, EN, D7, D6, D5, and D4 (with R/W pin permanently grounded for write operation). When you are engaged in a complex project bundled with large number of modules, you may face pin shortage for your microcontroller. In such situations, I2C LCD comes handy making use of only 2 pins (SDA & SCL) to talk to MCU, thereby saving atleast 4 pins. If you already have I2C devices, this LCD module actually uses no more pins at all.
Before moving further, lets see how an LCD can be controlled by I2C. In the image shown above, you can see a backpack module fitted to the back of the LCD. He does the work using an I/O expander PCF8574, that communicates with the micro-controller by I2C.
The PCF8574 provides general purpose remote I/O expansion for most microcontroller families via the two-line bidirectional bus (I2C-bus). The device consists of an 8-bit quasi-bidirectional port and an I2C-bus interface.
A quasi-bidirectional I/O can be used as an input or output without the use of a control signal for data direction. The PCF8574 has a low current consumption and includes latched outputs with high current drive capability. It also possesses an interrupt line (INT) which can be connected to the interrupt logic of the microcontroller. By sending an interrupt signal on this line, the remote I/O can inform the microcontroller if there is incoming data on its ports without having to communicate via the I2C-bus. This means that the PCF8574 can remain a simple slave device.
You can use this with LCD modules that have a HD44780-compatible interface with various screen sizes. The key is that your LCD must have the interface pads in a single row of sixteen, so it matches the pins on the backpack.
The three hardware address pins A0, A1 and A2 allow eight devices to be on the same I2C-bus. You can change the address of the device according to the status of each of these pins. The default address of the device is 0X3F (with PCF8574AT).
Note that backpack modules centered around PCF8574/PCF8574T (SO16 package of PCF8574 in DIP16 package) have a default slave address of 0×27. For those with PCF8574A/PCF8574AT chip, the default slave address will change to 0x3F.
Sample code for 16×2 LCD is given below. Upload the sketch to your Arduino board and you can see the LCD working. For 20×4 LCD, use the commented setup and comment the current setup.
Normally an LCD is operated in 4 bit or 8 bit parallel pin mode. The PCF chip is connected to the LCD data and control lines. And the driver sends the proper I2C commands to control the LCD. This way you can use I2C which is great since it can be used of a greater distance.