A small library to interact with keypads connected to GPIO pins.

Its really just a defined behavior macro to make setting up a keypad very easy to get up a running. In theory, this can be used on any platform with GPIO pins, but is mainly developed with the raspberry pi in mind.

It can be used with membrane or mechanical keypads, such as these:

• Adafruit 3x4 Matrix Membrane Keypad
• Adafruit 1x4 Matrix Membrane Keypad
• Adafruit 4x4 Matrix Keypad

If you want to know more about how it works, I found this article to be very helpful. In short, keypads are split into rows and columns and work by changing the pin state HIGH/LOW on keypress. You then traverse your known pins and match it to a predefined matrix of characters to determine which button is actually being pressed.

⚠️ keypad sets the internal pull-up resistors on raspberry pi so you can plug every pin of the keypad directly into the board. However, that is currently hardware dependent and not supported for other boards. For those, see the setup for determining your pinout and setup.

Add keypad to your list of dependencies in mix.exs:

def deps do
  [
    {:keypad, "~> 0.3"}
  ]
end

keypad is a small GenServer to handle receiving messages from GPIO pins via Circuits.GPIO and then reacting to them. keypad only implements the logic of reacting to pin state change and finding which character it correlates to. It does not host any logic what to do with that value and expects a handle_keypress/1 function to be implemented to receive the deduced key presses.

It comes with some common predefined matricies of characters so assuming you are using the default row and column GPIO pins, you can make a simple module like so:

defmodule MyModule do
  use Keypad, size: :four_by_four

  @impl true
  def handle_keypress(key, _), do: IO.inspect(key, label: "KEYPRESS: )
end

Then in an iex session, start your keypad procss and start pressing buttons

$ MyModule.start_link

# Press some buttons
KEYPRESS: 1
KEYPRESS: 5
...

For more complex configuration and examples, see the configuration doc.