# Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Overview ![](https://cdn-learn.adafruit.com/assets/assets/000/116/096/medium800thumb/adafruit_products_PCF8575_in_use_large.jpg?1666395104) Expand your project possibilities, with the  **Adafruit PCF8575 GPIO Expander Breakout**  - an affordable 16 channel I2C expander. ![](https://cdn-learn.adafruit.com/assets/assets/000/116/097/medium800/adafruit_products_PCF8575_top_angle.jpg?1666395422) GPIO expanders work like this: you have a board with some number of GPIO but not enough for your project - maybe you need more buttons or LEDs. [You _could_ upgrade to a board with massive number of GPIO like the Grand Central](https://www.adafruit.com/?q=grand+central&sort=BestMatch), or you could pop on one of these boards. Connect it over I2C and then you can send/receive I2C commands to control the GPIO pins to write and read them. It's going to be slower than direct GPIO access, but maybe that doesn't matter if it takes a millisecond instead of a microsecond. You only need the two I2C pins, and you can even share the I2C port with other sensors and devices. Heck, you can even add more expanders for massive I/O control! ![](https://cdn-learn.adafruit.com/assets/assets/000/116/098/medium800/adafruit_products_PCF8575_back.jpg?1666395469) The PCF8575 is a common and _slightly unusual _I2C expander for folks who are used to the [MCP230xx series](https://www.adafruit.com/?q=mcp%20e&sort=BestMatch): - First up, it's very affordable - who doesn't love that? - It has 16 I/O pins - Three I2C address select jumpers mean up to 8 expanders to one bus for 128 total GPIO added - Each pin can be an input with light pull-up or an output sink - IRQ output will automatically alert you when input pins change value - This chip does not have a pin direction register. You cannot set the pins as input or output - instead, each pin has two possible states. Basically, you can think of it as an open-drain output with a 100K resistor pull-up built in. - Option one: Lightly pulled up 'input' - by default it will read as a high logic level, but connecting the GPIO to ground will cause it to read as a low logic level. - Option two: Strong 20mA low-driving transistor sink output. This means the output is 'forced' to be low and will always read as a low logic level. ![](https://cdn-learn.adafruit.com/assets/assets/000/116/099/medium800/adafruit_products_PCF8575_top_header.jpg?1666395484) The pin direction / state thing is a little odd but it actually works fine for many purposes as long as you know what to expect. For example, if you want to read a button or switch, connect one side to the PCF and the other side to ground. Then set the pin to 'light pull-up input' When the button is pressed it will read low, when released it will read high. If you want to control an LED, connect the anode to positive voltage through a resistor. When the PCF pin is set to 'light pull-up input' the LED will be off. When the PCF pin is set to 'strong ground output' the LED will connect to ground and turn on. If you want to send a GPIO output logic level to some other device or peripheral, the light pull-up acts as high logic out, the strong ground output acts as low logic out. If you want to receive a GPIO input logic level, set the pin to light pull-up and then read the pin to determine if the GPIO input is high or low. ![](https://cdn-learn.adafruit.com/assets/assets/000/116/101/medium800/adafruit_products_PCF8575_top.jpg?1666395523) Basically, the only thing to watch for is you cannot drive an LED that is expecting the expander GPIO to go high to turn on the LED or connect a button input to a positive voltage without adding an additional pull-down resistor. If this is a bit confusing, worry not - all this stuff is taken care of for you in our [Arduino PCF8574/5](https://github.com/adafruit/Adafruit_PCF8574) library or [CircuitPython/Python PCF8575 library](https://github.com/adafruit/Adafruit_CircuitPython_PCF8575) - you can pretend it has input/output modes and the library will fake out what you are expecting. ![](https://cdn-learn.adafruit.com/assets/assets/000/116/100/medium800/adafruit_products_PCF8575_STEMMA_side.jpg?1666395493) To get you going fast, we spun up a custom-made PCB in the [**STEMMA QT**  form factor](https://www.adafruit.com/?q=stemma%20qt%20sensor "STEMMA QT form factor"), making it easy to interface with. The [STEMMA QT connectors](https://learn.adafruit.com/introducing-adafruit-stemma-qt/what-is-stemma-qt) on either side are compatible with the [SparkFun Qwiic](https://www.sparkfun.com/qwiic) I2C connectors. This allows you to make solderless connections between your development board and the PCF8575 or to chain it with a wide range of other sensors and accessories using a [**compatible cable**](https://www.adafruit.com/?q=stemma%20qt%20cable). [**QT Cable is not included** , but we have a variety in the shop](https://www.adafruit.com/?q=stemma+qt+cable&sort=BestMatch).  # Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Pinouts ![](https://cdn-learn.adafruit.com/assets/assets/000/116/227/medium800/adafruit_products_PCF8575_pinouts_guide.jpg?1666809847) The default I2C address is **0x20**. ## Power Pins ![](https://cdn-learn.adafruit.com/assets/assets/000/116/228/medium800/adafruit_products_PCF8575_power_pins.jpg?1666811114) - **VIN** - This is the power pin. To power the board, give it the same power as the logic level of your microcontroller - i.e. for a 5V micro like Arduino, use 5V, or for a 3V micro like a Feather, use 3V. - **GND** - This is common ground for power and logic. ## I2C Logic Pins ![](https://cdn-learn.adafruit.com/assets/assets/000/116/229/medium800/adafruit_products_PCF8575_I2C_pins.jpg?1666811150) - **SCL** - I2C clock pin, connect to your microcontroller I2C clock line. This pin uses the same logic level as the VIN pin, and there's a **10K pullup** on this pin. - **SDA** - I2C data pin, connect to your microcontroller's I2C data line. This pin uses the same logic level as the VIN pin, and there's a **10K pullup** on this pin. ## STEMMA QT Connectors ![](https://cdn-learn.adafruit.com/assets/assets/000/116/230/medium800/adafruit_products_PCF8575_STEMMA_QT.jpg?1666811182) - [**STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) **-** These connectors on the left and right ends of the breakout allow you to connect to development boards with **STEMMA QT** connectors, or to other things, with [various associated accessories](https://www.adafruit.com/category/619). ## Expander Pins ![](https://cdn-learn.adafruit.com/assets/assets/000/116/231/medium800/adafruit_products_PCF8575_expander_pins.jpg?1666811227) This breakout has a total of **16 I/O expander pins** available. - Along the bottom are the first **8 I/O pins** for expanding your project. They are labeled below the pads, left-to-right as **P0 through P7**. - Along the top are the second **8 I/O pins** for expanding your project. They are labeled above the pads, left to right as **15 through 10** and **P9 and P8**. ## Expander Power Pins ![](https://cdn-learn.adafruit.com/assets/assets/000/116/232/medium800/adafruit_products_PCF8575_exp_power_rails.jpg?1666811265) - Above the bottom set of I/O pins is the **ground pins** for the expander I/O pins. Highlighted in white on the silk, they are labeled to the left of the row with a **-** in a circle, and above the right end of the row with **GND**. - Below the top set of I/O pins is the **positive voltage** for the expander I/O pins. Highlighted in white on the silk, they are labeled to the left of the row with a **+** in a circle, and below the right end of the row with **VCC (same as VIN)**. ## Address Pin and Jumpers ![](https://cdn-learn.adafruit.com/assets/assets/000/116/233/medium800/adafruit_products_PCF8575_address_jumpers.jpg?1666811550) ![](https://cdn-learn.adafruit.com/assets/assets/000/116/234/medium800/adafruit_products_PCF8575_address_pins.jpg?1666811575) - On the back of the board are **three address jumpers** , labeled **A0** , **A1** , and **A2**. These jumpers allow you to chain up to 8 of these boards on the same pair of I2C clock and data pins. To do so, you solder the jumpers "closed" by connecting the two pads, in various combinations. - On the front of the board are  **three** **address pins** , labeled **A0** , **A1** , and **A2**. Just like the jumpers, these pins allow you to change the I2C address to connect multiple boards by connecting them to VIN in various combinations. The default I2C address is **0x20**. The other address options can be calculated by “adding” the **A0/A1/A2**  to the base of **0x20**. **A0** sets the lowest bit with a value of **1** , **A1** sets the next bit with a value of **2** and **A2** sets the next bit with a value of **4.** The final address is **0x20 + A2 + A1 + A0** which would be **0x27**. 
So for example if **A2** is soldered closed and **A0** is soldered closed, the address is **0x20 + 4 + 1 = 0x25**. 
If only **A0** is soldered closed, the address is **0x20 + 1 = 0x21** 
If only **A1** is soldered closed, the address is **0x20 + 2 = 0x22** 
If only **A2** is soldered closed, the address is **0x20 + 4 = 0x24** The table below shows all possible addresses, and whether the pin(s) or jumper(s) should be high (closed) or low (open). ![](https://cdn-learn.adafruit.com/assets/assets/000/113/870/medium800/adafruit_products_PCF8574_possible_I2C_addresses.png?1659461197) ## INT Pin ![](https://cdn-learn.adafruit.com/assets/assets/000/116/235/medium800/adafruit_products_PCF8575_IRQ_pin.jpg?1666811680) - The **INT** pin is the IRQ output, which will automatically alert you when input pins change value. ## On LED and LED Jumper ![](https://cdn-learn.adafruit.com/assets/assets/000/116/236/medium800/adafruit_products_PCF8575_on_LED.jpg?1666811721) ![](https://cdn-learn.adafruit.com/assets/assets/000/116/237/medium800/adafruit_products_PCF8575_LED_jumper.jpg?1666811733) - On the left side of the front of the board is the **on LED** which lights up when the board has power. It is labeled to the left of the LED as **on**. - Towards the right side of the back of the board is the **LED jumper**. It is **two pads connected by a trace** , labeled as  **LED ** to the left of the pads. If you'd rather not have the on LED lit up when the board has power, you can cut the trace between the two pads. To reenable the on LED, you can bridge the pads again with solder. ## PCF8575 Chip ![](https://cdn-learn.adafruit.com/assets/assets/000/116/238/medium800/adafruit_products_PCF8575_onboard_chip.jpg?1666811797) - The grey square to the left of center of the breakout is the **PCF8575 I/O expander chip**. This is what provides you with all of the expansion features of this board. # Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Python & CircuitPython It's easy to use the **Adafruit** **PCF8575** with Python or CircuitPython, and the [Adafruit CircuitPython PCF8575](https://github.com/adafruit/Adafruit_CircuitPython_PCF8575) module. This module allows you to easily write Python code that enables you to utilize the 16 I/O pins on the expander. You can use this sensor with any CircuitPython microcontroller board or with a computer that has GPIO and Python [thanks to Adafruit\_Blinka, our CircuitPython-for-Python compatibility library](https://learn.adafruit.com/circuitpython-on-raspberrypi-linux). ## CircuitPython Microcontroller Wiring First wire up a PCF8575 to your board exactly as shown below. These wiring diagrams include a button and an LED, which are necessary for the example below. Here's an example of wiring a Feather RP2040 to the expander with I2C using one of the handy [**STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) connectors: **Feather to expander** : - Simply use a [STEMMA QT cable](https://www.adafruit.com/product/4399) to connect from **the STEMMA QT connector on the microcontroller** to the **STEMMA QT connector on the breakout**. Follow the [steps below](https://learn.adafruit.com/adafruit-pcf8574/python-circuitpython#step-3123166) to connect the LED and button. ![adafruit_products_PCF8575_Feather_STEMMA_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/243/medium640/adafruit_products_PCF8575_Feather_STEMMA_bb.jpg?1666909918) You can also use the standard **0.100" pitch** headers to wire it up on a breadboard: **Feather to expander** : - **Feather 3V**  to **expander VIN (red wire)** - **Feather GND**  to **expander GND (black wire)** - **Feather SCL**  to **expander SCL (yellow wire)** - **Feather SDA**  to **expander SDA (blue wire)** Follow the [steps below](https://learn.adafruit.com/adafruit-pcf8574/python-circuitpython#step-3123166) to connect the LED and button. ![adafruit_products_PCF8575_Feather_breadboard_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/244/medium640/adafruit_products_PCF8575_Feather_breadboard_bb.jpg?1666909955) Connect the LED and the button to the expander as follows: **LED to expander:** - **LED+** to **expander P8** - **LED-** to **470Ω resistor** - **470Ω resistor** to **+ row on** **expander** **Button to expander:** - **One leg of button** to **- row on expander** - **Opposite leg of button** to **expander P0** ![adafruit_products_PCF8575_button_LED_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/245/medium640/adafruit_products_PCF8575_button_LED_bb.jpg?1666910038) ## Python Computer Wiring Since there's _dozens_ of Linux computers/boards you can use, we will show wiring for Raspberry Pi. For other platforms, [please visit the guide for CircuitPython on Linux to see whether your platform is supported](https://learn.adafruit.com/circuitpython-on-raspberrypi-linux).  These wiring diagrams include a button and an LED, which are necessary for the example below. Here's the Raspberry Pi wired to the expander using I2C and a [**STEMMA QT**](https://learn.adafruit.com/introducing-adafruit-stemma-qt) connector. **Pi to expander:** - **Pi 3V**  to **expander VIN (red wire)** - **Pi GND**  to **expander GND (black wire)** - **Pi SCL**  to **expander SCL (yellow wire)** - **Pi SDA**  to **expander SDA (blue wire)** Follow the [steps above](https://learn.adafruit.com/adafruit-pcf8574/python-circuitpython#step-3123166) to connect the LED and button. ![adafruit_products_PCF8575_RasPi_STEMMA_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/246/medium640/adafruit_products_PCF8575_RasPi_STEMMA_bb.jpg?1666910101) Finally here is an example of how to wire up a Raspberry Pi to the expander using a solderless breadboard: **Pi to expander:** - **Pi 3V**  to **expander VIN (red wire)** - **Pi GND**  to **expander GND (black wire)** - **Pi SCL**  to **expander SCL (yellow wire)** - **Pi SDA**  to **expander SDA (blue wire)** Follow the [steps above](https://learn.adafruit.com/adafruit-pcf8574/python-circuitpython#step-3123166) to connect the LED and button. ![adafruit_products_PCF8575_RasPi_breadboard_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/247/medium640/adafruit_products_PCF8575_RasPi_breadboard_bb.jpg?1666910126) ## Python Installation of PCF8575 Library You'll need to install the **Adafruit\_Blinka** library that provides the CircuitPython support in Python. This may also require enabling I2C on your platform and verifying you are running Python 3. [Since each platform is a little different, and Linux changes often, please visit the CircuitPython on Linux guide to get your computer ready](https://learn.adafruit.com/circuitpython-on-raspberrypi-linux)! Once that's done, from your command line run the following command: - `pip3 install adafruit-circuitpython-pcf8575` If your default Python is version 3, you may need to run `pip` instead. Make sure you aren't trying to use CircuitPython on Python 2.x, it isn't supported! ## CircuitPython Usage To use with CircuitPython, you need to first install the PCF8575 library, and its dependencies, into the **lib** folder on your **CIRCUITPY** drive. Then you need to update **code.py** with the example script. Thankfully, we can do this in one go. In the example below, click the **Download Project Bundle** button below to download the necessary libraries and the **code.py** file in a zip file. Plug your computer into the microcontroller board with a known good USB cable (with data+power wiring). Extract the contents of the zip file, and copy the **entire** **lib** **folder** and the **code.py** file to your **CIRCUITPY** drive. Your **CIRCUITPY/lib** folder should contain the following folder and file: - **adafruit\_bus\_device/** - **adafruit\_pcf8575.mpy** ![CIRCUITPY](https://adafruit.github.io/Adafruit_CircuitPython_Bundle/pcf8575_pcf8575_simpletest.py.png ) ## Python Usage Once you have the library `pip3` installed on your computer, copy or download the following example to your computer, and run the following, replacing **code.py** with whatever you named the file: `python3 code.py` ## Example Code https://github.com/adafruit/Adafruit_CircuitPython_PCF8575/blob/main/examples/pcf8575_buttonled.py Now, press the button to see the LED light up. That's all there is to using the PCF8574 with CircuitPython! # Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Python Docs # Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Arduino Using the PCF8575 with Arduino involves wiring up the sensor to your Arduino-compatible microcontroller, installing the [Adafruit PCF8574](https://github.com/adafruit/Adafruit_PCF8574) library (which supports the PCF8575 as well!) and running the provided example code. ## Wiring Wire as shown for a **5V** board like an Uno. If you are using a **3V** board, like an Adafruit Feather, wire the board's 3V pin to the PCF8575 VIN. These wiring diagrams include a button and an LED, which are necessary for the example below. Here is an Adafruit Metro wired up to the PCF8575 using the STEMMA QT connector: **Metro to expander** : Use a [STEMMA QT to male header pin cable](https://www.adafruit.com/product/4209). - **Metro 5V**  to **expander VIN (red wire)** - **Metro GND**  to **expander GND (black wire)** - **Metro SCL**  to **expander SCL (yellow wire)** - **Metro SDA**  to **expander SDA (blue wire)** - **Metro 2** to **expander INT (purple wire)** Please follow the [steps below](https://learn.adafruit.com/adafruit-pcf8574/arduino#step-3123278) for LED and button wiring. ![adafruit_products_PCF8575_Arduino_STEMMA_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/324/medium640/adafruit_products_PCF8575_Arduino_STEMMA_bb.jpg?1666986036) Here is an Adafruit Metro wired up using a solderless breadboard: **Metro to expander** : - **Metro 5V**  to **expander VIN (red wire)** - **Metro GND**  to **expander GND (black wire)** - **Metro SCL**  to **expander SCL (yellow wire)** - **Metro SDA**  to **expander SDA (blue wire)** - **Metro 2** to **expander INT (purple wire)** Please follow the [steps below](https://learn.adafruit.com/adafruit-pcf8574/arduino#step-3123278) for LED and button wiring. ![adafruit_products_PCF8575_Arduino_breadboard_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/323/medium640/adafruit_products_PCF8575_Arduino_breadboard_bb.jpg?1666985997) Connect the LED and the button to the expander as follows: **LED to expander:** - **LED+** to **expander P8** - **LED-** to **470Ω resistor** - **470Ω resistor** to **+ row on** **expander** **Button to expander:** - **One leg of button** to **- row on expander** - **Opposite leg of button** to **expander P0** ![adafruit_products_PCF8575_button_LED_bb.jpg](https://cdn-learn.adafruit.com/assets/assets/000/116/322/medium640/adafruit_products_PCF8575_button_LED_bb.jpg?1666985731) ## Library Installation You can install the **PCF8574** library for Arduino using the Library Manager in the Arduino IDE. ![](https://cdn-learn.adafruit.com/assets/assets/000/113/950/medium800/adafruit_products_Arduino_Open_Library_Manager.png?1659548784) Click the  **Manage Libraries ...** menu item, search for **PCF8574** , and select the **Adafruit PCF8574** library: ![](https://cdn-learn.adafruit.com/assets/assets/000/113/951/medium800/adafruit_products_PCF8574_Arudino_lib_install.png?1659548798) When asked about dependencies, click "Install all". ![](https://cdn-learn.adafruit.com/assets/assets/000/113/952/medium800/adafruit_products_PCF8574_Arduino_lib_dependencies.png?1659548843) ## Load Example Open up **File** **-\> Examples -\> Adafruit PCF8574 -\> pcf8575\_buttonledirq** and upload to your Arduino wired to the sensor. https://github.com/adafruit/Adafruit_PCF8574/blob/main/examples/pcf8575_buttonledirq/pcf8575_buttonledirq.ino Once loaded, press the button to see the LED light up when the button is pressed. The GIF below shows a "lazy" way to wire up a button and LED. You should always use a resistor when wiring up an LED! ![](https://cdn-learn.adafruit.com/assets/assets/000/116/325/medium800thumb/adafruit_products_PCF8575_in_use_large.jpg?1666986228 This shows the PCF8575 wired to a Metro Mini, with two LEDs, but the concept is the same for the example above.) # Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Arduino Docs # Adafruit PCF8575 I2C 16 GPIO Expander Breakout ## Downloads ## Files - [PCF8575 Datasheet](https://cdn-learn.adafruit.com/assets/assets/000/116/239/original/pcf8575_datasheet.pdf?1666814391) - [EagleCAD PCB files on GitHub](https://github.com/adafruit/Adafruit-PCF8575-PCB) - [Fritzing object in the Adafruit Fritzing Library](https://github.com/adafruit/Fritzing-Library/blob/master/parts/Adafruit%20PCF8575.fzpz) ## Schematic and Fab Print ![](https://cdn-learn.adafruit.com/assets/assets/000/116/240/medium800/adafruit_products_PCF8575_sch.png?1666814824) ![](https://cdn-learn.adafruit.com/assets/assets/000/116/241/medium800/adafruit_products_PCF8575_fab_print.png?1666814837 Measurements in inches.) ## Primary Products ### Adafruit PCF8575 I2C 16 GPIO Expander Breakout [Adafruit PCF8575 I2C 16 GPIO Expander Breakout](https://www.adafruit.com/product/5611) Expand your project possibilities, with the  **Adafruit PCF8575 GPIO Expander Breakout**  - an affordable 16 channel I2C expander. GPIO expanders work like this: you have a board with some number of GPIO but not enough for your project - maybe you need more... In Stock [Buy Now](https://www.adafruit.com/product/5611) [Related Guides to the Product](https://learn.adafruit.com/products/5611/guides) ## Related Guides - [Adafruit RP2040 CAN Bus Feather](https://learn.adafruit.com/adafruit-rp2040-can-bus-feather.md) - [QT Py Lego](https://learn.adafruit.com/qt-py-lego.md) - [Adafruit 1-Wire GPIO Breakout - DS2413](https://learn.adafruit.com/adafruit-1-wire-gpio-breakout-ds2413.md) - [Using DVI Video in CircuitPython](https://learn.adafruit.com/using-dvi-video-in-circuitpython.md) - [PyBadge Conference Badge With Unicode Fonts](https://learn.adafruit.com/pybadge-conference-badge-multi-language-unicode-fonts.md) - [Playing Arduboy Games on Arcada](https://learn.adafruit.com/playing-arduboy-games-on-arcada.md) - [Adafruit HTS221 - Temperature & Humidity Sensor](https://learn.adafruit.com/adafruit-hts221-temperature-humidity-sensor.md) - [Optical Sensor Drum Track Sequencer](https://learn.adafruit.com/drum-track-sequencer.md) - [LED Bullwhip with Motion & Sound Reactivity](https://learn.adafruit.com/led-bullwhip.md) - [Adafruit ESP32-S2 TFT Feather](https://learn.adafruit.com/adafruit-esp32-s2-tft-feather.md) - [Adafruit MLX90632 FIR Remote Thermal Temperature Sensor](https://learn.adafruit.com/adafruit-mlx90632-fir-remote-thermal-temperature-sensor.md) - [DS1307 Real Time Clock Breakout Board Kit](https://learn.adafruit.com/ds1307-real-time-clock-breakout-board-kit.md) - [ESP32-S2 Reverse TFT Digital Clock Display featuring Blanka-chan!](https://learn.adafruit.com/esp32-s2-tft-digital-clock-display-featuring-blanka-chan.md) - [MCUME Emulators on Fruit Jam](https://learn.adafruit.com/mcume-emulators-on-fruit-jam.md) - [Control Wiz Lights With CircuitPython](https://learn.adafruit.com/control-wiz-lights-with-circuitpython.md)