Pico Four Keypad

by John Park

published October 14, 2021, last updated October 14, 2021

posted in Hacks Gaming CircuitPython Programming/ MicroPython / CircuitPython

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Beginner

Project guide

Code the Four Keypad

Text Editor

Adafruit recommends using the Mu editor for using your CircuitPython code with the Pico. You can get more info in this guide.

Alternatively, you can use any text editor that saves files.

CircuitPython Code

Copy the code below and paste it into Mu. Then, save it to your Pico as code.py.

Note that you must change a couple of lines of code to switch between Mac and Windows.

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# SPDX-FileCopyrightText: 2021 john park for Adafruit Industries
# SPDX-License-Identifier: MIT
# Pico Four Key USB HID Keypad

import board
from digitalio import DigitalInOut, Pull
from adafruit_debouncer import Debouncer
import usb_hid
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keycode import Keycode

kpd = Keyboard(usb_hid.devices)

# Choose the correct modifier key for Windows or Mac.
# Comment one line and uncomment the other.
# MODIFIER = Keycode.CONTROL  # For Windows
MODIFIER = Keycode.COMMAND  # For Mac

# define buttons
NUM_KEYS = 4
PINS = (
    board.GP0,
    board.GP1,
    board.GP2,
    board.GP3,
)

KEYMAP = (
    ("Select all", [MODIFIER, Keycode.A]),
    ("Cut", [MODIFIER, Keycode.X]),
    ("Copy", [MODIFIER, Keycode.C]),
    ("Paste", [MODIFIER, Keycode.V]),
)

keys = []
for pin in PINS:
    dio = DigitalInOut(pin)
    dio.pull = Pull.UP
    keys.append(Debouncer(dio))

print("\nWelcome to keypad")
print("keymap:")
for k in range(NUM_KEYS):
    print("\t", (KEYMAP[k][0]))


while True:
    for i in range(NUM_KEYS):
        keys[i].update()
        if keys[i].fell:
            print(KEYMAP[i][0])
            kpd.send(*KEYMAP[i][1])

# SPDX-FileCopyrightText: 2021 john park for Adafruit Industries
# SPDX-License-Identifier: MIT
# Pico Four Key USB HID Keypad

import board
from digitalio import DigitalInOut, Pull
from adafruit_debouncer import Debouncer
import usb_hid
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keycode import Keycode

kpd = Keyboard(usb_hid.devices)

# Choose the correct modifier key for Windows or Mac.
# Comment one line and uncomment the other.
# MODIFIER = Keycode.CONTROL  # For Windows
MODIFIER = Keycode.COMMAND  # For Mac

# define buttons
NUM_KEYS = 4
PINS = (
    board.GP0,
    board.GP1,
    board.GP2,
    board.GP3,
)

KEYMAP = (
    ("Select all", [MODIFIER, Keycode.A]),
    ("Cut", [MODIFIER, Keycode.X]),
    ("Copy", [MODIFIER, Keycode.C]),
    ("Paste", [MODIFIER, Keycode.V]),
)

keys = []
for pin in PINS:
    dio = DigitalInOut(pin)
    dio.pull = Pull.UP
    keys.append(Debouncer(dio))

print("\nWelcome to keypad")
print("keymap:")
for k in range(NUM_KEYS):
    print("\t", (KEYMAP[k][0]))


while True:
    for i in range(NUM_KEYS):
        keys[i].update()
        if keys[i].fell:
            print(KEYMAP[i][0])
            kpd.send(*KEYMAP[i][1])

Testing

Even before we've wired up the mechanical keyswitches, you can test the code by shorting each of the four GPIO pins used to ground. This is the same as pressing a key. Just be careful not to short power to ground!

Use a text editor with some text in it to watch as your keys select all, cut, copy, and paste!

USB keyboards and mice show up on your computer as 'HID' devices, which stands for 'Human Interface Device'

HID Keyboard Basics

This guide page has a great intro to CircuitPython HID Keyboard.

For even more details, check out the documentation at https://circuitpython.readthedocs.io/projects/hid/en/latest/ which includes all of the keycodes and media codes you can use.

By importing the adafruit_hid library into the program, you can make calls to send keyboard keys and media keys.

Customization

You can have your keypad type other keys or key combos if you like. This is the section of code to adjust:

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KEYMAP = (
    ("Select all", [MODIFIER, Keycode.A]),
    ("Cut", [MODIFIER, Keycode.X]),
    ("Copy", [MODIFIER, Keycode.C]),
    ("Paste", [MODIFIER, Keycode.V]),
)

KEYMAP = (
    ("Select all", [MODIFIER, Keycode.A]),
    ("Cut", [MODIFIER, Keycode.X]),
    ("Copy", [MODIFIER, Keycode.C]),
    ("Paste", [MODIFIER, Keycode.V]),
)

The string is only there for debugging/testing purposes. The section inside the brackets is where you can put your own keys and combos. Just remember to add a comma between each key in a combo.