Device Type:sensor

Electrical Standard:eu global

Difficulty:Soldering required (4/5)

Shelly H&T Gen3

Product Image

Battery-powered WiFi temperature/humidity sensor with a segment E-Paper display (UC8119 controller). Uses an ESP32-C3 with 8MB flash, a Sensirion SHT31 sensor, and a UltraChip UC8119 E-Paper segment display with 91 active segments, 10 digits and 13 icons.

Requires custom ESPHome external components for the UC8119 display and Shelly H&T display layer.

GPIO Pinout

GPIO	Function	Notes
GPIO0	Button	XTAL_32K_P, ext. pull-up, deep sleep wakeup
GPIO1	I2C SDA	Shared bus (SHT31 + UC8119), ext. pull-up
GPIO2	Power Rail ADC	Reads regulated 3.3V rail, not battery
GPIO3	I2C SCL	100kHz, external pull-up on FPC
GPIO4	Battery ADC	Via voltage divider (÷3), GPIO18 enable
GPIO5	Battery Presence	HIGH when batteries are connected
GPIO6	UC8119 BUSY_N	LOW=busy, external pull-up on FPC
GPIO7	UC8119 RESET_N	Active LOW, 10ms pulse
GPIO8	USB Detect	HIGH=USB connected, LOW=battery
GPIO10	UC8119 Enable	Display power gate, HIGH=on
GPIO18	Batt Power En	Enables power-path for battery ADC

I2C Devices

Device	Address	Function
SHT31	0x44	Temperature & Humidity
UC8119	0x50	E-Paper Segment Display

Serial Pinout (PCB Test Pads)

UART Pinout

The UART pads are bare test points on the PCB (no header installed). Use pogo pins, test clips, or solder temporary wires for flashing.

Pad	Function
1	NC
2	RXD
3	CHIP_EN
4	GND
5	TXD
6	VCC 3V3
7	BOOT / GPIO9

Flashing

Note: OTA flashing from the original Shelly firmware is not possible. Shelly Gen3 verifies OTA images with an ECDSA signature using their private key. The device must be flashed via UART using the PCB test pads.

To enter download mode, short pad 7 (GPIO9) to pad 4 (GND) while powering on the device. Release after boot.

Backup the Original Firmware

Always back up the original firmware before flashing:

esptool.py --chip esp32c3 --port /dev/ttyUSB0 --baud 460800 \
  --before no-reset --after no-reset \
  read_flash 0 0x800000 shelly-ht-gen3-backup.bin

Compile and Flash

esphome compile shelly-ht-gen3.yaml
esptool.py --chip esp32c3 --port /dev/ttyUSB0 --baud 460800 \
  write_flash 0x0 .esphome/build/shelly-ht-gen3/.pioenvs/shelly-ht-gen3/firmware-factory.bin

Basic Configuration (USB Powered)

esphome:
  name: shelly-ht-gen3
  friendly_name: "Shelly H&T Gen3"

esp32:
  board: esp32-c3-devkitm-1
  variant: ESP32C3
  flash_size: 8MB
  framework:
    type: esp-idf
    version: recommended
    sdkconfig_options:
      COMPILER_OPTIMIZATION_SIZE: y
    advanced:
      enable_ota_rollback: false

logger:
wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
api:
ota:
  - platform: esphome
    on_begin:
      - lambda: id(display).show_ota_begin();
    on_progress:
      - lambda: id(display).show_ota_progress(x);
    on_end:
      - lambda: id(display).show_ota_end();
    on_error:
      - lambda: id(display).show_ota_error();

external_components:
  - source: github://oxynatOr/esphome-shelly_ht_gen3
    components: [shelly_ht_display]
    refresh: 5s
  - source: github://oxynatOr/esphome-uc8119
    components: [uc8119]
    refresh: 5s

i2c:
  sda: GPIO1
  scl: GPIO3
  scan: false
  frequency: 100kHz

sensor:
  - platform: sht3xd
    address: 0x44
    temperature:
      name: "Temperature"
      id: temp_sensor
      accuracy_decimals: 1
    humidity:
      name: "Humidity"
      id: humi_sensor
      accuracy_decimals: 0
    update_interval: 60s

  - platform: wifi_signal
    name: "WiFi Signal"
    id: wifi_rssi
    update_interval: 120s

  - platform: adc
    id: batt_adc
    pin: GPIO4
    attenuation: 12db
    update_interval: never
    internal: true
    samples: 15

time:
  - platform: homeassistant
    id: ha_time

# Layer 1: Generic UC8119 EPD segment display driver
uc8119:
  id: epd
  address: 0x50
  reset_pin: GPIO7
  busy_pin: GPIO6
  enable_pin: GPIO10
  ghost_clear_interval: 8h
  full_update_every: 360

# Layer 2: Shelly-specific display logic
shelly_ht_display:
  id: display
  display_id: epd
  update_interval: 1sec
  wifi_update_every: 20
  font: siekoo
  battery_adc_sensor: batt_adc
  battery_presence_sensor: batt_presence
  battery_power_enable: batt_power_en
  battery_divider: 3
  battery_full_voltage: 6.0
  battery_empty_voltage: 4.0
  battery_update_interval: 15sec
  battery_voltage:
    name: "Battery Voltage"
  battery_percent:
    name: "Battery Percent"
  external_power:
    name: "External Power"
  temperature_sensor: temp_sensor
  humidity_sensor: humi_sensor
  wifi_signal_sensor: wifi_rssi
  time_id: ha_time

output:
  - platform: gpio
    id: batt_power_en
    pin: GPIO18

binary_sensor:
  - platform: gpio
    id: batt_presence
    pin:
      number: GPIO5
      inverted: true
    internal: true

  - platform: gpio
    name: "Button"
    pin:
      number: GPIO0
      mode:
        input: true
        pullup: true
      inverted: true
      allow_other_uses: true
    filters:
      - delayed_on_off: 50ms

button:
  - platform: restart
    name: "Restart"

Battery Powered Configuration (Deep Sleep)

esphome:
  name: shelly-ht-gen3
  friendly_name: "Shelly H&T Gen3"
  on_boot:
    priority: -200
    then:
      - if:
          condition:
            binary_sensor.is_off: batt_presence
          then:
            - deep_sleep.prevent: deep_sleep_ctrl
  on_shutdown:
    then:
      - lambda: id(epd).power_off();

esp32:
  board: esp32-c3-devkitm-1
  variant: ESP32C3
  flash_size: 8MB
  framework:
    type: esp-idf
    version: recommended
    sdkconfig_options:
      COMPILER_OPTIMIZATION_SIZE: y
    advanced:
      enable_ota_rollback: false

logger:
wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password
api:
ota:
  - platform: esphome
    on_begin:
      - lambda: id(display).show_ota_begin();
    on_progress:
      - lambda: id(display).show_ota_progress(x);
    on_end:
      - lambda: id(display).show_ota_end();
    on_error:
      - lambda: id(display).show_ota_error();

external_components:
  - source: github://oxynatOr/esphome-shelly_ht_gen3
    components: [shelly_ht_display]
    refresh: 5s
  - source: github://oxynatOr/esphome-uc8119
    components: [uc8119]
    refresh: 5s

deep_sleep:
  id: deep_sleep_ctrl
  run_duration: 20s
  sleep_duration: 1min
  wakeup_pin:
    - pin:
        number: GPIO0
        mode:
          input: true
          pullup: true
        inverted: true
        allow_other_uses: true

i2c:
  sda: GPIO1
  scl: GPIO3
  scan: false
  frequency: 100kHz

sensor:
  - platform: sht3xd
    address: 0x44
    temperature:
      name: "Temperature"
      id: temp_sensor
      accuracy_decimals: 1
    humidity:
      name: "Humidity"
      id: humi_sensor
      accuracy_decimals: 0
    update_interval: 10s

  - platform: wifi_signal
    name: "WiFi Signal"
    id: wifi_rssi
    update_interval: 120s

  - platform: adc
    id: batt_adc
    pin: GPIO4
    attenuation: 12db
    update_interval: never
    internal: true
    samples: 15

time:
  - platform: homeassistant
    id: ha_time

# Layer 1: Generic UC8119 EPD segment display driver
uc8119:
  id: epd
  address: 0x50
  reset_pin: GPIO7
  busy_pin: GPIO6
  enable_pin: GPIO10
  ghost_clear_interval: 8h
  full_update_every: 360

# Layer 2: Shelly-specific display logic
shelly_ht_display:
  id: display
  display_id: epd
  update_interval: 1sec
  wifi_update_every: 20
  font: siekoo
  battery_adc_sensor: batt_adc
  battery_presence_sensor: batt_presence
  battery_power_enable: batt_power_en
  battery_divider: 3
  battery_full_voltage: 6.0
  battery_empty_voltage: 4.0
  battery_update_interval: 15sec
  battery_voltage:
    name: "Battery Voltage"
  battery_percent:
    name: "Battery Percent"
  external_power:
    name: "External Power"
  temperature_sensor: temp_sensor
  humidity_sensor: humi_sensor
  wifi_signal_sensor: wifi_rssi
  time_id: ha_time
  on_ready:
    then:
      - lambda: id(epd).power_off();
      - deep_sleep.enter: deep_sleep_ctrl

output:
  - platform: gpio
    id: batt_power_en
    pin: GPIO18

binary_sensor:
  - platform: gpio
    id: batt_presence
    pin:
      number: GPIO5
      inverted: true
    internal: true

  - platform: gpio
    name: "Button"
    pin:
      number: GPIO0
      mode:
        input: true
        pullup: true
      inverted: true
      allow_other_uses: true
    filters:
      - delayed_on_off: 50ms

button:
  - platform: restart
    name: "Restart"

Display Layout

The UC8119 segment display has the following layout (all segments shown):

+--------------------------------------------+
|                                            |
|  88:88            Arrow  Battery           |
|  T1 T2 : T3 T4     ^    [||||]             |
|                                            |
|  88.8              [8] °                   |
|  D1 D2 . D3       UNIT (C/F)               |
|  Temperature                               |
|                                            |
|  Frost Heat Vent  ?  Calendar              |
|   *     ~    @    =    #                   |
|                                            |
|  Signal  BT  Globe      88 %               |
|  ||||    *    @         H1 H2              |
|                         Humidity           |
|                                            |
+--------------------------------------------+

Zones:

Zone	Digits	Function
Top left	T1 T2 : T3 T4	Clock (HH:MM)
Top right	Arrow + Battery	Arrow, 5-segment battery
Center left	D1 D2 . D3	Temperature (XX.X)
Center right	UNIT	°C/°F (small digit + °)
Icon row 1	❄ ♨ ❀ ☰ 📅	Frost, Heat, Vent, ?, Cal
Icon row 2	Signal, BT, Globe	WiFi, Bluetooth, Globe
Bottom right	H1 H2 %	Humidity (XX%)

Battery Measurement

The battery voltage is measured via GPIO4 (ADC1) through a voltage divider (÷3). The measurement circuit requires GPIO18 to be set HIGH to enable the power path before reading. The component handles this automatically via the battery_power_enable output.

4× AA (LR6): 4.0V (empty) to 6.4V (fresh)
ADC range: ~1.33V to ~2.13V after divider
GPIO5: Battery presence (HIGH when connected)
GPIO8: USB detection (HIGH when USB connected)

Deep Sleep Behavior

The component auto-detects deep sleep mode from the YAML config:

WiFi wake (every Nth cycle): Full boot, HA time sync (~5s)
Non-WiFi wake (other cycles): No WiFi, RTC time, fast (~1.5s)
USB connected: Deep sleep prevented, always-on mode
Button press (GPIO0): Wakes device from deep sleep

The on_ready trigger fires after non-WiFi display updates, allowing the YAML to control when to enter deep sleep. The on_shutdown handler saves the framebuffer to RTC memory, enabling partial refresh on the next wake (no white flash).

Known Limitations

OTA from Shelly firmware not possible: ECDSA signature verification prevents flashing ESPHome OTA from stock firmware. UART flashing required.
Battery percentage accuracy: The voltage-to-percentage mapping may need calibration for your battery chemistry and temperature. Default range (4.0V–6.0V) is for 4× AA alkaline batteries.

Shelly H&T Gen3​

GPIO Pinout​

I2C Devices​

Serial Pinout (PCB Test Pads)​

Flashing​

Backup the Original Firmware​

Compile and Flash​

Basic Configuration (USB Powered)​

Battery Powered Configuration (Deep Sleep)​

Display Layout​

Battery Measurement​

Deep Sleep Behavior​

Known Limitations​