LilyGoT7S3 + PCF8574 + 3x4 Keypad issues

ESPHome
1

Hi everyone. I’ve been struggling with an issue for a few days and I can’t seem to figure it out. I’m trying to connect a 3×4 membrane keypad to a PCF8574 IO expander, which is connected to my LilyGo T7 S3 via Stemma QT.

The keypad wiring is correct — if I connect the keypad directly to the board, it works without any problems. However, when I connect it through the PCF8574 over I2C, nothing happens. The I2C address is set correctly, but I don’t see any logs or key events when I press the keypad buttons. I’m still very new to this, so please bear with me. (I know nothing about pullups, pulldowns for example?)

I can confirm that the PCF8574 itself is working, because if I connect a simple button to one of its pins, I do get logs when pressing it. Does anyone have an idea of what I might be missing?

Here is my minimal YAML which I use for testing.

esp32:
  board: esp32-s3-devkitc-1
  framework:
    type: esp-idf

esphome:
  name: testingKeyboard
  name_add_mac_suffix: true

logger:
  level: DEBUG

matrix_keypad:
  id: mykeypad

  rows:
    - pin:
        pcf8574: expander_keypad
        number: 1
    - pin:
        pcf8574: expander_keypad
        number: 6
    - pin:
        pcf8574: expander_keypad
        number: 5
    - pin:
        pcf8574: expander_keypad
        number: 3

  columns:
    - pin:
        pcf8574: expander_keypad
        number: 2
    - pin:
        pcf8574: expander_keypad
        number: 0
    - pin:
        pcf8574: expander_keypad
        number: 4

  keys: "123456789*0#"
  has_diodes: false

  on_key:
    - lambda: |-
        ESP_LOGI("Keypad", "Key pressed: %c", x);

i2c:
  - id: bus_a
    sda: GPIO14
    scl: GPIO13
    frequency: 100kHz
    scan: true

pcf8574:
  - id: expander_keypad
    address: 0x24
    i2c_id: bus_a
    pcf8575: false
2

You might need to set the pins to INPUT. When I use the IO extender, I always set the INPUT/OUTPUT mode.

switch:
  - platform: gpio
    name: "WZ Plug #0"
    id: wz_plug0
    pin:
      pcf8574: WZEightChannelExtender
      # Use pin number 0
      number: 0
      # One of INPUT or OUTPUT
      mode:
        output: true
      inverted: true

in your case

rows:
    - pin:
        pcf8574: expander_keypad
        number: 1
        mode:
          input: true
        inverted: false
    - pin:
        pcf8574: expander_keypad
        number: 6
        mode:
          input: true
        inverted: false
	...