The I2C Serial Interface Module is an expansion board built around the PCF8574T 8-bit I/O expander IC. Designed specifically to solder directly to character LCD displays (such as 1602 or 2004 modules), it converts a standard 16-pin parallel interface into a simple 2-wire I2C interface (SDA and SCL). This dramatically reduces the number of microcontroller GPIO pins required to drive a display down to just two communication lines.

Specifications

• Driver IC: PCF8574T (I2C-to-Parallel I/O Expander)
• Operating Voltage: 2.5V to 6.0V DC (5V recommended for LCDs)
• Default I2C Address: Typically 0x27 or 0x3F (Depending on the chip variant and board revision)
• Address Configuration: 3 solder jumper pads (A0, A1, A2) allowing up to 8 unique addresses on a single I2C bus
• Display Compatibility: Supports standard HD44780-compatible LCD screens (1602, 2004, 1604)
• Backlight Control: Onboard jumper header to enable/disable the backlight, plus software control
• Contrast Adjustment: Built-in multi-turn potentiometer for manual display contrast tuning

Interface and Pinout Guide

Input Side (Connects to Microcontroller)

• GND: Common Ground Reference
• VCC: Power Supply Input (5V DC recommended)
• SDA: I2C Serial Data Line (Connects to MCU SDA pin)
• SCL: I2C Serial Clock Line (Connects to MCU SCL pin)

Output Side (Solders to 1602/2004 LCD)

• Pins 1 to 16: Connects directly to the corresponding pins (VSS, VDD, V0, RS, RW, E, D0–D7, A, K) on the LCD board, operating in 4-bit parallel data mode.

Address Selection Guide (Solder Pads A0, A1, A2)

The board features three address selection pads labelled A0, A1, and A2. By default, these pads are open (unbridged). Bridging a pad connects it to GND, altering the 7-bit I2C address:

• Default (A0, A1, A2 Open): 0x27 (or 0x3F on PCF8574AT chips)
• Bridge A0: Decrements base address by 1
• Bridge A1: Decrements base address by 2
• Bridge A2: Decrements base address by 4

Key Features

• Drastic Pin Count Reduction: Replaces up to 10 digital I/O lines required for 4-bit/8-bit parallel LCD setups with just 2 I2C signal wires (SDA/SCL).
• Adjustable Contrast: Includes an integrated top-adjust potentiometer, allowing effortless calibration of character readability without adding external resistors.
• Flexible Address Allocation: Configurable address pads permit up to 8 individual LCD modules to run simultaneously on the same two-wire I2C bus line.
• Onboard Backlight Jumper: Features a physical jumper block that can be pulled off to completely cut backlight power for energy-sensitive battery applications.

Common Applications

• Embedded System Displays: Outputting system parameters, sensor logs, and diagnostics on desktop testing rigs.
• Smart Home Control Panels: Displaying real-time temperature, humidity, and status readings in home automation projects.
• User Interface Interfaces: Providing readable status updates for 3D printers, CNC controllers, and robotics hubs.
• Benchtop Instruments: Creating compact visual readouts for custom digital power supplies, frequency counters, and voltmeters.

Usage Tips

• Address Scanning: If your code fails to print text on the screen, run a standard "I2C Scanner" sketch on your microcontroller to confirm the exact address (usually 0x27 or 0x3F).
• Contrast Calibration: If you only see blank illuminated boxes or nothing at all when powered up, use a small screwdriver to turn the blue potentiometer until the character outlines become crisp and clear.
• Pull-Up Resistors: The board usually includes onboard I2C pull-up resistors. However, if you are running multiple modules on long wire runs, ensure your SDA and SCL lines have stable pull-ups to the VCC rail.