PCF8575 IO Expander Module I2C To 16IO For Arduino

Specifications:

• Operating Voltage: 2.5V to 5.5V DC
• Communication Interface: I2C (SDA, SCL)
• I2C Clock Frequency: Up to 400 kHz (Fast-mode)
• Number of Added I/O Pins: 16 (P00–P07, P10–P17)
• Pin Type: Quasi-bidirectional digital I/O
• Maximum Sink Current (Per Pin): 25mA
• Default I2C Address: 0x20
• Configurable I2C Addresses: 0x20 to 0x27 (via A0, A1, A2 solder pads)
• Compatible Platforms: Arduino, ESP32, Raspberry Pi, STM32

Unlock New Capabilities

• Past Projects If you've already experimented with complex Arduino builds involving multiple sensors, buttons, and displays, you have likely encountered the dreaded "pin shortage." When your Arduino Uno or ESP32 simply doesn't have enough digital GPIO pins left to connect everything, you are ready to explore I2C bus expansion.
• Feature Upgrade This PCF8575 IO Expander unlocks the ability to build massive hardware interfaces using only two pins on your microcontroller. It is the perfect backbone for wiring up 16-channel relay controllers, full-sized custom hardware keyboards, complex smart-home control panels, or LED status matrices without having to upgrade to a much larger, more expensive board like an Arduino Mega.
• Effort Level & Minimum Hardware
• Effort Level: Intermediate

Minimum hardware to get started:

• Microcontroller (Arduino/ESP32): to send and receive bitwise data over the I2C protocol.
• 4× Female-to-Male Jumper Wires: to connect the VCC, GND, SDA, and SCL pins between the expander module and your development board.
• Soldering Iron & Solder: to permanently attach the included male header pins to the expander board for breadboard prototyping.

Included in the Box:

• 1× PCF8575 I2C to 16-Pin I/O Expander Module
• Straight Male Header Pins (requires soldering)

Frequently Asked Questions

• Is the PCF8575 compatible with standard Arduino boards like the Uno and Mega?
  Yes, it works flawlessly with any Arduino board that supports standard I2C communication.
• Can I use this expander module with a 3.3V ESP32 or ESP8266?
  Yes, the module operates safely down to 2.5V, making it natively compatible with 3.3V logic without needing a level shifter.
• Does this module work with the Raspberry Pi?
  Yes, you can connect it to the Pi's I2C pins and control it using Python libraries like smbus.
• Can I use the extended pins for PWM output to fade LEDs?
  No, the PCF8575 only provides basic digital ON/OFF logic and does not support hardware PWM on its expansion pins.
• What voltage should I supply to the VCC pin?
  You should supply the same voltage that your microcontroller's logic uses, typically 3.3V or 5V.
• How much current can a single extended pin handle?
  Each pin can sink a maximum of 25mA when pulling a load to ground, but can only source a very small amount of current.
• Can I power 16 standard LEDs directly from this board?
  Yes, provided you wire them in a current-sinking configuration (anodes to VCC, cathodes through a resistor to the PCF8575 pins).
• How do I connect the module to my microcontroller?
  You only need four wires: VCC for power, GND for common ground, and the SDA and SCL pins for I2C data and clock.
• Do I need external pull-up resistors on the SDA and SCL lines?
  The module typically includes onboard pull-up resistors, so external ones are rarely needed unless your I2C bus is very long.
• What do the A0, A1, and A2 solder pads do?
  They allow you to change the I2C address of the module by soldering the pads to high or low, preventing conflicts if you use multiple expanders.
• Do I have to write the raw I2C bitwise commands myself?
  No, while you can use the standard Wire.h library, installing a dedicated PCF8575 library makes coding much simpler.
• What is the default I2C address of this module?
  If the A0, A1, and A2 pads are left unsoldered, the default 7-bit I2C address is usually 0x20.
• How do I read an input, like a push button, using this module?
  You set the specific pin high in your code, and when the external button pulls it to ground, the PCF8575 registers it as a low input.