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Shift Registers

You can build a PLC-like device with many inputs and outputs using 74HC165 and 74HC595 shift registers. This is ideal for scenarios where you need dozens of GPIO pins for switches, sensors, or actuators, but have limited physical pins on your microcontroller.

Goal​

We'll create a reusable library file using an .eta template to generate a customizable number of inputs and outputs.

  • The number of inputs and outputs will be the same for simplicity.
  • Binary sensors and switches will have auto-generated IDs using the pattern:
    input_{chip_index}_{pin_index} and output_{chip_index}_{pin_index}
    (e.g. input_00_0, output_03_7, etc.)
  • Some inputs will have customized names and automations

Shift Registers Library​

Here's what the library file might look like:

PLC/.lib/shift.eta
<%-
  const toDec = (number) => number?.toString(10)?.padStart(2, '0');
  const pinToId = (chip, pin) => `${toDec(chip)}_${pin%8}`;
-%>

sn74hc165:
  - id: sn74hc165_hub
    data_pin: 9 
    clock_pin: 11
    load_pin: 10
    sr_count: <%= it.count*2 %>

binary_sensor:
<%- for (var i_chip = 0; i_chip < it.count; i_chip++) { %>
<%- for (var i_pin = 0; i_pin < 8; i_pin++) { %>
  - platform: gpio
    id: input_<%= pinToId(i_chip, i_pin) %>
    pin:
      sn74hc165: sn74hc165_hub
      number: <%= i_chip*8 + i_pin %>
      inverted: true
<%- } %>
<%- } %>

sn74hc595:
  - id: sn74hc595_hub
    data_pin: 12
    clock_pin: 13
    latch_pin: 14
    sr_count: <%= it.count %>

switch:
<%- for (var i_chip = 0; i_chip < it.count; i_chip++) { %>
<%- for (var i_pin = 0; i_pin < 8; i_pin++) { %>
  - platform: gpio
    id: output_<%= pinToId(i_chip, i_pin) %>
    pin:
      sn74hc595: sn74hc595_hub
      number: <%= i_chip*8 + i_pin %>
<%- } %>
<%- } %>

Device Inputs/Outputs​

PLC/IOs.eta
<%~ include('./.lib/shift', { count: 8 }) %>

With just a few lines of templated code, we’ve generated 80 binary sensors and 80 switches. This dramatically reduces boilerplate and makes your configuration scalable and maintainable.

YAML Patch​

warning

This feature is experimental and may change in future versions.

When you use templates to generate components (like a large batch of sensors or switches), the result is fast — but not always flexible. For example, you can't easily change individual names, add automations, or customize behavior per input/output.

That’s where YAML Patch comes in.

YAML Patch lets you modify specific parts of the generated YAML before it's uploaded to ESPHome. It acts as a post-processing step — targeting nodes by their IDs and applying changes to them.

You can patch:

  • The name or ay other property of a component
  • Add on_press, on_click, or other automation triggers
  • Override default options
  • Add device-specific settings

Let’s say you want to change the name of the binary sensor with ID input_03_2. You can patch that — and multiple other components — in the same file:

- $.switch[?(@.id=="output_01_2")]:
    - set:
        name: "Ceiling light"
- $.binary_sensor[?(@.id=="input_05_1")]:
    - set:
        name: "Wall button"
    - set:
        on_state:
            then:
                - switch.toggle: output_01_2

How It Works

  1. All YAMLs are generated as usual.
  2. Editor 4 ESPHome scans the device directory for .patch files.
  3. Each patch file is applied to the device YAML config.
  4. The final YAML is assembled.