SN74HC595 I/O Expander (shift register)
=======================================

.. seo::
    :description: Instructions for setting up SN74HC595 shift registers as digital port expanders in ESPHome.

The SN74HC595 component allows you to use SN74HC595 shift registers as I/O expanders
(`datasheet <http://www.ti.com/lit/ds/symlink/sn74hc595.pdf>`__,
`SparkFun`_) in ESPHome. It uses 3 wires (optionally 4) for communication. Optionally, it can be added
to a SPI bus to allow sharing pins with other components.

Once configured, you can use any of the 8 pins for your projects. Up to 256 shift registers can be daisy-chained
to provide more pins, without using more GPIO pins on the controller.

Use of the OE pin is optional. If used, the pin should be pulled up externally.

.. figure:: images/sn74hc595-full.jpg
    :align: center
    :width: 80.0%

    SN74HC595 I/O Expander (shift register).

.. _SparkFun: https://www.sparkfun.com/products/13699

The component can be configured using :ref:`GPIO pins <config-pin_schema>` or the :ref:`SPI Bus <spi>`.

Over GPIO
---------

.. code-block:: yaml

    # Example configuration entry
    sn74hc595:
      - id: 'sn74hc595_hub'
        data_pin: GPIOXX
        clock_pin: GPIOXX
        latch_pin: GPIOXX
        oe_pin: GPIOXX
        sr_count: 2

    # Individual outputs
    switch:
      - platform: gpio
        name: "SN74HC595 Pin #0"
        pin:
          sn74hc595: sn74hc595_hub
          # Use pin number 0
          number: 0
          inverted: false

Configuration variables:
************************

- **id** (**Required**, :ref:`config-id`): The id to use for this SN74HC595 component.
- **data_pin** (**Required**, :ref:`Pin Schema <config-pin_schema>`): Pin connected to SN74HC595 SER (SD) input.
- **clock_pin** (**Required**, :ref:`Pin Schema <config-pin_schema>`): Pin connected to SN74HC595 SRCLK (SH_CP) pin
- **latch_pin** (**Required**, :ref:`Pin Schema <config-pin_schema>`): Pin connected to SN74HC595 RCLK (ST_CP) pin
- **oe_pin** (*Optional*, :ref:`Pin Schema <config-pin_schema>`): Pin connected to SN74HC595 OE pin
- **sr_count** (*Optional*, int): Number of daisy-chained shift registers, up-to 256. Defaults to ``1``.

Over SPI
--------

.. code-block:: yaml

    # Example configuration entry
    sn74hc595:
      - id: 'sn74hc595_hub'
        type: spi
        latch_pin: GPIOXX
        oe_pin: GPIOXX
        sr_count: 2


Configuration variables:
************************

- **id** (**Required**, :ref:`config-id`): The id to use for this SN74HC595 component.
- **spi_id** (**Required**, :ref:`SPI Bus Schema <spi>`): The SPI bus to use. This will automatically be set to the ID of the SPI bus if there is only one.
- **type** (**Required**, string): Must be ``spi``.
- **latch_pin** (**Required**, :ref:`Pin Schema <config-pin_schema>`): Pin connected to SN74HC595 RCLK (ST_CP) pin
- **oe_pin** (*Optional*, :ref:`Pin Schema <config-pin_schema>`): Pin connected to SN74HC595 OE pin
- **sr_count** (*Optional*, int): Number of daisy-chained shift registers, up to 256. Defaults to ``1``.


Pin configuration
-----------------

.. code-block:: yaml

    # Individual outputs
    switch:
      - platform: gpio
        name: "SN74HC595 Pin #0"
        pin:
          sn74hc595: sn74hc595_hub
          # Use pin number 0
          number: 0
          inverted: false


- **sn74hc595** (**Required**, :ref:`config-id`): The id of the SN74HC595 component of the pin.
- **number** (**Required**, int): The pin number.
- **inverted** (*Optional*, boolean): If all written values should be treated as inverted.
  Defaults to ``false``.


See Also
--------

- :doc:`switch/gpio`
- :doc:`binary_sensor/gpio`
- `Serial to Parallel Shifting-Out with a 74HC595 <https://www.arduino.cc/en/tutorial/ShiftOut>`__
- :apiref:`sn74hc595/sn74hc595.h`
- :ghedit:`Edit`