This component was developed because ESPHome has no native support for the Shelly Plus Add-On's dual-GPIO 1-Wire interface, which uses galvanic isolation with separate TX and RX pins.

Supported Devices

Device	Chip	1-Wire TX	1-Wire RX	Analog IN	Digital IN
Shelly 2PM Gen3	ESP32-C3	GPIO9	GPIO21	GPIO20	GPIO1
Shelly 1PM Gen3	ESP32-C3	GPIO9	GPIO21	GPIO20	GPIO1
Shelly Plus 1/1PM	ESP32	GPIO0	GPIO1	GPIO3	GPIO19/22
Shelly Plus 2PM	ESP32	GPIO0	GPIO1	GPIO3	GPIO22

Note: GPIO assignments vary between device generations. Gen3 devices use different pins than Plus devices!

Why This Component?

The Shelly Plus Add-On uses an ISO7221A dual digital isolator for galvanic isolation. This splits the bidirectional 1-Wire protocol into separate TX (output) and RX (input) paths. Standard ESPHome dallas or one_wire components don't support this dual-pin configuration.

How It Works

ESP32                    ISO7221A                  DS18B20
┌──────┐                ┌────────┐                ┌───────┐
│ TX ──┼───► Isolator ──┼──► ────┼───► Data ◄────┤       │
│      │                │        │                │       │
│ RX ◄─┼──── Isolator ◄─┼──── ◄──┼──── Data ◄────┤       │
└──────┘                └────────┘                └───────┘

Installation

Option 1: External Component (Recommended)

Add to your ESPHome YAML:

external_components:
  - source:
      type: git
      url: https://github.com/majoto85/esphome-shelly-plus-addon
      ref: main
    components: [shelly_dallas]

Option 2: Local Component

Copy the components/shelly_dallas folder to your ESPHome configuration directory under custom_components/ or local_components/.

external_components:
  - source:
      type: local
      path: local_components
    components: [shelly_dallas]

Configuration

Complete Example for Shelly 2PM Gen3

substitutions:
  device_name: shelly-2pm-gen3

esphome:
  name: ${device_name}

esp32:
  variant: esp32c3
  flash_size: 8MB
  framework:
    type: esp-idf
    version: recommended

# External component for Shelly Plus Add-On
external_components:
  - source:
      type: local
      path: local_components
    components: [shelly_dallas]

# I2C for ADE7953 power monitoring
i2c:
  sda: GPIO6
  scl: GPIO7

# 1-Wire bus for DS18B20 temperature sensors
shelly_dallas:
  pin_tx: GPIO9
  pin_rx: GPIO21
  update_interval: 30s

sensor:
  # DS18B20 Temperature Sensor
  - platform: shelly_dallas
    name: "Temperature"
    resolution: 12
    # Optional: specify address if multiple sensors
    # address: 0x28XXXXXXXXXXXX

  # Analog Input (0-10V as duty cycle)
  - platform: duty_cycle
    pin: GPIO20
    name: "Analog IN Duty"
    id: addon_analog_duty
    unit_of_measurement: "%"
    update_interval: 1s

  # Convert duty cycle to voltage
  - platform: template
    name: "Analog IN Voltage"
    unit_of_measurement: "V"
    lambda: 'return id(addon_analog_duty).state * 0.1;'

binary_sensor:
  # Digital Input
  - platform: gpio
    pin:
      number: GPIO1
      mode: input
    name: "Digital IN"
    filters:
      - delayed_on_off: 50ms

DS18B20 Sensor Options

sensor:
  - platform: shelly_dallas
    name: "My Temperature Sensor"

    # Resolution: 9-12 bits (higher = more accurate but slower)
    resolution: 12

    # Error tolerance: keep last valid value for N consecutive errors
    # before publishing NaN (default: 5)
    max_errors: 5

    # For multiple sensors, specify the address
    address: 0x28FF1234567890AB

    # Or use index (0 = first sensor found)
    # index: 0

    # Standard ESPHome sensor options
    unit_of_measurement: "°C"
    accuracy_decimals: 2
    filters:
      - sliding_window_moving_average:
          window_size: 5
          send_every: 1

Error Tolerance

Due to the timing-critical nature of the 1-Wire protocol through galvanic isolation, occasional read errors may occur. The component includes built-in error tolerance:

Last valid value: On read errors (CRC, bus reset failure), the sensor keeps publishing the last valid temperature
Consecutive error count: Only after max_errors consecutive failures, the sensor publishes NaN
Automatic recovery: When a successful read occurs, the error counter resets

This prevents brief glitches from causing automations to trigger unexpectedly.

Log output example:

[W] CRC error reading scratchpad (error 1/5, keeping 23.50°C)
[W] Bus reset failed (error 2/5, keeping 23.50°C)
[D] Temperature: 23.56 °C (raw: 377)  # Success, counter reset

GPIO Reference

Shelly 2PM Gen3 (ESP32-C3)

GPIO	Function	Notes
GPIO0	ADE7953 Reset	Power meter
GPIO1	Add-On Digital IN	Directly usable (shared with ADE7953 IRQ)
GPIO3	Relay 1	Channel 1 output
GPIO4	NTC Temperature	Internal device temperature
GPIO5	Relay 2	Channel 2 output
GPIO6	I2C SDA	For ADE7953
GPIO7	I2C SCL	For ADE7953
GPIO9	Add-On 1-Wire TX	DS18B20 output
GPIO10	Switch Input 1	Physical input
GPIO18	Switch Input 2	Physical input
GPIO19	Reset Button	-
GPIO20	Add-On Analog IN	As PWM/duty cycle
GPIO21	Add-On 1-Wire RX	DS18B20 input

Shelly Plus 1PM / Plus 2PM (ESP32)

GPIO	Function
GPIO0	Add-On 1-Wire TX
GPIO1	Add-On 1-Wire RX
GPIO3	Add-On Analog IN
GPIO19/22	Add-On Digital IN

Analog Input Details

The Shelly Plus Add-On converts the 0-10V analog input to a PWM signal due to galvanic isolation:

Uses a sawtooth waveform generator and comparator
Output duty cycle is proportional to input voltage
0V = 0% duty cycle
10V = 100% duty cycle

Read it with ESPHome's duty_cycle sensor and convert to voltage:

sensor:
  - platform: duty_cycle
    pin: GPIO20
    name: "Analog Raw"
    id: analog_duty

  - platform: template
    name: "Analog Voltage"
    unit_of_measurement: "V"
    lambda: 'return id(analog_duty).state * 0.1;'

Troubleshooting

No sensors found

Check wiring: VCC, DATA, GND on the Add-On's 1-Wire terminals
Verify GPIO pins match your device (Gen3 vs Plus)
Check logs for "Bus reset result: DEVICE PRESENT"

CRC errors

Usually indicates timing issues or poor connections
Try shorter wires or add a 4.7kΩ pull-up resistor on the data line
Occasional CRC errors are normal - the component tolerates up to max_errors consecutive failures before publishing NaN
Increase max_errors if you see frequent but recoverable errors

Sensor shows NaN

Only occurs after max_errors consecutive read failures (default: 5)
Check wiring and connections
Try increasing max_errors for noisy environments
Increase update_interval if conversion timeouts occur
Check that only one component uses the 1-Wire GPIOs

Relay/automation triggers unexpectedly

If automations react to brief NaN values, increase max_errors to provide more tolerance
Example: max_errors: 10 keeps the last valid value for up to 10 consecutive failures

Technical Details

1-Wire Protocol Timing

Based on Tasmota's proven implementation:

Operation	Duration
Reset pulse	480µs low
Presence detect	70µs wait, sample
Write '1'	10µs low, 55µs release
Write '0'	65µs low, 5µs release
Read bit	3µs low, sample at 12µs

Supported Sensor Families

0x28: DS18B20 (most common)
0x10: DS18S20
0x22: DS1822

Credits

This component was developed with assistance from Claude (Anthropic) through collaborative debugging and research of:

Special thanks to the Tasmota community for documenting the Shelly Gen3 GPIO pinouts.

License

MIT License - See LICENSE file.

Contributing

Contributions are welcome! Please:

Test on your hardware before submitting
Include your device model and GPIO configuration
Add documentation for new devices

README.md

ESPHome Shelly Plus Add-On Component