Adafruit TCA8418 Keypad Matrix and GPIO Expander Breakout

by Liz Clark

published September 21, 2022, last updated September 21, 2022

posted in Adafruit Products Arduino Compatibles CircuitPython Breakout Boards STEMMA

Updated

Beginner

Product guide

Python & CircuitPython

It's easy to use the TCA8418 with Python or CircuitPython, and the Adafruit_CircuitPython_TCA8418 module. This module allows you to easily write Python code that reads the TCA8418's GPIO pins as a GPIO expander or keypad matrix. You can use this breakout with any CircuitPython microcontroller board or with a computer that has GPIO and Python thanks to Adafruit_Blinka, our CircuitPython-for-Python compatibility library.

CircuitPython Microcontroller Wiring

First, wire up a TCA8418 and keypad to your board exactly as shown below. Here's an example of wiring a Feather M4 to the breakout with I2C using one of the handy STEMMA QT connectors:

TCA8418

Board 3V to breakout VIN (red wire)
Board GND to breakout GND (black wire)
Board SCL to breakout SCL (yellow wire)
Board SDA to breakout SDA (blue wire)

Keypad

Pin 1 to breakout C3
Pin 2 to breakout C2
Pin 3 to breakout C1
Pin 4 to breakout C0
Pin 5 to breakout R2
Pin 6 to breakout R1
Pin 7 to breakout R0

You can also use standard 0.100" pitch headers to wire it up on a breadboard:

TCA8418

Board 3V to breakout VIN (red wire)
Board GND to breakout GND (black wire)
Board SCL to breakout SCL (yellow wire)
Board SDA to breakout SDA (blue wire)

Keypad

Pin 1 to breakout C3
Pin 2 to breakout C2
Pin 3 to breakout C1
Pin 4 to breakout C0
Pin 5 to breakout R2
Pin 6 to breakout R1
Pin 7 to breakout R0

Python Computer Wiring

Since there's dozens of Linux computers/boards you can use, below shows wiring for Raspberry Pi. For other platforms, please visit the guide for CircuitPython on Linux to see whether your platform is supported.

Here's the Raspberry Pi wired to the breakout using I2C and a STEMMA QT connector:

TCA8418

Pi 3V to breakout VIN (red wire)
Pi GND to breakout GND (black wire)
Pi SCL to breakout SCL (yellow wire)
Pi SDA to breakout SDA (blue wire)

Keypad

Pin 1 to breakout C3
Pin 2 to breakout C2
Pin 3 to breakout C1
Pin 4 to breakout C0
Pin 5 to breakout R2
Pin 6 to breakout R1
Pin 7 to breakout R0

Finally here is an example of how to wire up a Raspberry Pi to the sensor using a solderless breadboard:

TCA8418

Pi 3V to breakout VIN (red wire)
Pi GND to breakout GND (black wire)
Pi SCL to breakout SCL (yellow wire)
Pi SDA to breakout SDA (blue wire)

Keypad

Pin 1 to breakout C3
Pin 2 to breakout C2
Pin 3 to breakout C1
Pin 4 to breakout C0
Pin 5 to breakout R2
Pin 6 to breakout R1
Pin 7 to breakout R0

Python Installation of TCA8418 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!

Once that's done, from your command line run the following command:

pip3 install adafruit-circuitpython-tca8418

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 TCA8418 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. 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 folders and file:

adafruit_bus_device/
adafruit_register/
adafruit_tca8418.mpy

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

Keypad Example Code

Download Project Bundle

Copy Code

# SPDX-FileCopyrightText: Copyright (c) 2022 Liz Clark for Adafruit Industries
#
# SPDX-License-Identifier: Unlicense

import time
import board
from adafruit_tca8418 import TCA8418

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
tca = TCA8418(i2c)

keymap = (("*", "0", "#"), ("7", "8", "9"), ("4", "5", "6"), ("1", "2", "3"))

# set up all R0-R2 pins and C0-C3 pins as keypads
KEYPADPINS = (
    TCA8418.R0,
    TCA8418.R1,
    TCA8418.R2,
    TCA8418.C0,
    TCA8418.C1,
    TCA8418.C2,
    TCA8418.C3,
)

# make them inputs with pullups
for pin in KEYPADPINS:
    tca.keypad_mode[pin] = True
    # make sure the key pins generate FIFO events
    tca.enable_int[pin] = True
    # we will stick events into the FIFO queue
    tca.event_mode_fifo[pin] = True

# turn on INT output pin
tca.key_intenable = True

while True:
    if tca.key_int:
        # first figure out how big the queue is
        events = tca.events_count
        # now print keyevent, row, column & key name
        for _ in range(events):
            keyevent = tca.next_event
            #  strip keyevent
            event = keyevent & 0x7F
            event -= 1
            #  figure out row
            row = event // 10
            #  figure out column
            col = event % 10
            #  print event type first
            if keyevent & 0x80:
                print("Key down")
            else:
                print("Key up")
            #  use row & column coordinates to print key name
            print("Row %d, Column %d, Key %s" % (row, col, keymap[col][row]))
        tca.key_int = True  # clear the IRQ by writing 1 to it
        time.sleep(0.01)

# SPDX-FileCopyrightText: Copyright (c) 2022 Liz Clark for Adafruit Industries
#
# SPDX-License-Identifier: Unlicense

import time
import board
from adafruit_tca8418 import TCA8418

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
tca = TCA8418(i2c)

keymap = (("*", "0", "#"), ("7", "8", "9"), ("4", "5", "6"), ("1", "2", "3"))

# set up all R0-R2 pins and C0-C3 pins as keypads
KEYPADPINS = (
    TCA8418.R0,
    TCA8418.R1,
    TCA8418.R2,
    TCA8418.C0,
    TCA8418.C1,
    TCA8418.C2,
    TCA8418.C3,
)

# make them inputs with pullups
for pin in KEYPADPINS:
    tca.keypad_mode[pin] = True
    # make sure the key pins generate FIFO events
    tca.enable_int[pin] = True
    # we will stick events into the FIFO queue
    tca.event_mode_fifo[pin] = True

# turn on INT output pin
tca.key_intenable = True

while True:
    if tca.key_int:
        # first figure out how big the queue is
        events = tca.events_count
        # now print keyevent, row, column & key name
        for _ in range(events):
            keyevent = tca.next_event
            #  strip keyevent
            event = keyevent & 0x7F
            event -= 1
            #  figure out row
            row = event // 10
            #  figure out column
            col = event % 10
            #  print event type first
            if keyevent & 0x80:
                print("Key down")
            else:
                print("Key up")
            #  use row & column coordinates to print key name
            print("Row %d, Column %d, Key %s" % (row, col, keymap[col][row]))
        tca.key_int = True  # clear the IRQ by writing 1 to it
        time.sleep(0.01)

If running CircuitPython: Once everything is saved to the CIRCUITPY drive, connect to the serial console to see the data printed out!

If running Python: The console output will appear wherever you are running Python.

In the example, the TCA8418 is instantiated on I2C. Then, the keypad matrix is setup. The key names are setup in a matrix as well.

In the loop, every time you press or release a key the key event is printed to the REPL, followed by the row, column and key name that was used in the event.

GPIO Expander Example Code

TCA8418

Board 3V to breakout VIN (red wire)
Board GND to breakout GND (black wire)
Board SCL to breakout SCL (yellow wire)
Board SDA to breakout SDA (blue wire)

LED

Anode to breakout R0 (green wire)
Cathode to board GND (black wire)

Button

Input to breakout R1 (pink wire)
GND to board GND (black wire)

Download Project Bundle

Copy Code

# SPDX-FileCopyrightText: Copyright (c) 2022 ladyada for Adafruit Industries
#
# SPDX-License-Identifier: Unlicense

import time
import board
from adafruit_tca8418 import TCA8418

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
tca = TCA8418(i2c)

# setup 2 gpio: LED on R0 and button in R1
OUTPIN = TCA8418.R0
INPIN = TCA8418.R1
tca.gpio_mode[OUTPIN] = True
tca.gpio_mode[INPIN] = True

# one is output, other is input with pullup
tca.gpio_direction[OUTPIN] = True
tca.gpio_direction[INPIN] = False
tca.pullup[INPIN] = True

# have LED mirror button
while True:
    tca.output_value[OUTPIN] = tca.input_value[INPIN]
    time.sleep(0.01)

# SPDX-FileCopyrightText: Copyright (c) 2022 ladyada for Adafruit Industries
#
# SPDX-License-Identifier: Unlicense

import time
import board
from adafruit_tca8418 import TCA8418

i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
tca = TCA8418(i2c)

# setup 2 gpio: LED on R0 and button in R1
OUTPIN = TCA8418.R0
INPIN = TCA8418.R1
tca.gpio_mode[OUTPIN] = True
tca.gpio_mode[INPIN] = True

# one is output, other is input with pullup
tca.gpio_direction[OUTPIN] = True
tca.gpio_direction[INPIN] = False
tca.pullup[INPIN] = True

# have LED mirror button
while True:
    tca.output_value[OUTPIN] = tca.input_value[INPIN]
    time.sleep(0.01)

In the GPIO expander example, the TCA8418 is instantiated on I2C. Then, R0 is setup as and output for the LED and R1 is setup as an input for the button.

In the loop, every time the button is pressed, the LED turns off. When the button is released, the LED turns on.