pcf8574 i2c lcd module pricelist

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.

Now available from PMD Way are these high-quality I2C interface-compatible LCD modules from PMD Way. Two rows of forty characters, with green text on a yellow background or white on blue. They are both 3.3V and 5V tolerant and perfect for your Arduino, Raspberry Pi or other projects.

These LCDs have been fitted with the adaptor and a PCF8574 I2C backpack interface, allowing you to use these on the I2C bus without any soldering - just plug and play to the four wires on thre backpack.

We may send one of two versions of this device - the difference is the controller IC. If you have the PCF8574T. the default I2C bus address is 0x27. If you have thePCF8574ATthe default I2C bus address is 0x3F.

A jumper on the back controls power to the backlight, and a contrast potentiometer is also fitted. No soldering is required, modules are fully assembled.

Adding a display to Raspberry PI Pico allows getting real time information from connected devices without using a computer from USB port. I2C LCD displays (with PCF8574 backpack) are one of best solution to keep wiring simple

I2C LCD displays are common LCD displays, usually composed of 16 columns x 2 rows blocks, but also different configurations can be found. Differently from simple LCD displays, they include a small panel soldered in its backside, including chips able to reduce their connection wires. The I2C LCD display usually has a PCF8574 chip, which is a device able to convert I2C serial communication into parallel connections.

To connect an I2C LCD Display with your Raspberry PI Pico, you just need to wire the Vcc and GND PINs from display to VSYS and a GND PINs of RPI Pico, then SDA and SCL PINs from the I2C Display to a couple of SDA and SCL PINs from Raspberry PI Pico, belonging to the same I2C bus, as shown in the picture on the following wiring diagram chapter.

A working solution uses the dhylands-python_lcd module including a generic API to interface to LCD displays. But this class implements commands to be sent to the LCD without caring about how to send them. The reason is that there are many different backpacks and every solution can be implemented in many different ways. The ones created with a PCF8574 use I2C as communication protocol, in this case, you need a sort of driver able to send commands via I2C. This function is implemented with a second module from T-622 user, also available from T-622 GitHub page.

Before going into the usage explanation, you have to be sure that your LCD’s I2C address is correct. This is a unique address shared between I2C devices to make them able to talk on the same shared wire. This is usually a hexadecimal value and all devices connected to your RPI Pico can be scanned by copy-paste of the following code in your Thonny shell (you can copy all lines together):

As I2C LCD with PCF8574 backpack use PCF8574 chip for I2C communication, you will probably get its default address (0x27). But if your project includes more PCF8574-based chips, then you will need to identify the LCD one between those that will be shown. In case of missing devices, please check your cabling.

Starting to use your LCD device, you can run a generic test with the T-622 test script, which I have pre-configured for 16×2 LCDs using I2C0 channel (ports GP0 and GP1 according to my wiring diagram). This modified script can be get from my download area (use the following link: i2c_lcd_test). Save this file in your Raspberry PI Pico root folder or in your computer and open it with Thonny IDE.

If you will see nothing, please check your cabling. Another common issue with I2C LCD display is getting a clean screen which is only powering on and off. This means that your connection is correct and everything is working, you have only to adjust your LCD contrast by rotating the screw positioned in your LCD backside, which controls a potentiometer managing contrast:

The LCD API used has a flexible feature allowing users to display also complex icons inside a single cell. Some special characters are already available and depend on your LCD ROM (Read Only Memory, space not visible to the user). You can use these chars with “lcd.putchar(chr())” function.

The first 8 characters (from 0 to 7) character-generator RAM. This means that you can define and design any icon you want to display by identifying pixels to be put on/off for each char block, made of 8 rows and 5 columns of pixels. Each row A good description of how to define a generic icon is explained in https://github.com/dhylands/python_lcd.

You can use the generated code with “lcd.custom_char()” command. An example usage is built in my pico_i2c_lcd script. Download and open it in your Thonny IDE.