The SHT45 is currently one of the most accurate temperature and humidity sensors available.
It offers laboratory-grade precision, ultra-low power consumption, and very stable measurements.

This guide shows you how to connect an ESP32 + SHT45 to Home Assistant using two methods:

1. ESPHome (best for most users — automatic integration)
2. MQTT (your current method — manual but flexible)

You can choose the method you prefer, and both can run on the same hardware.

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1. Hardware Required

• ESP32 DevKit (DOIT, WROOM, NodeMCU, etc.)
• SHT45 sensor
• 4× Female-to-female jumper wires
• USB cable
• (Optional) Breadboard

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2. Wiring the ESP32 to SHT45

SHT45 uses I2C.

ESP32 → SHT45
3.3V → VIN
GND  → GND
GPIO22 → SCL
GPIO21 → SDA

[Image: ESP32 connected to SHT45 wiring diagram]

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METHOD 1 — ESPHome (Recommended for Most Users)

If you use ESPHome, sensors appear automatically in Home Assistant.

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3. ESPHome Configuration (Working YAML)

Create or edit your ESPHome device and add the following blocks:

ESPHome YAML

esphome:
  name: esp32-sht45
  platform: ESP32
  board: esp32dev

wifi:
  ssid: "YOUR_WIFI"
  password: "YOUR_PASSWORD"

# Enable fallback hotspot
ap:
  ssid: "ESP32-SHT45-Fallback"

logger:
api:
ota:

i2c:
  sda: 21
  scl: 22
  scan: true

sensor:
  - platform: sht4x
    type: SHT45
    temperature:
      name: "SHT45 Temperature"
    humidity:
      name: "SHT45 Humidity"
    update_interval: 10s

Notes

✔ No MQTT needed → auto-discovered in HA
✔ Very stable readings
✔ Works instantly with minimal config

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METHOD 2 — MQTT

If you are using Home Assistant’s mqtt: section inside configuration.yaml, not ESPHome YAML.
Below is the correct SHT45 YAML written in the same format as your working BME280 sensors.

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4. Home Assistant configuration.yaml (Correct MQTT Syntax)

Add these entries under your existing:

mqtt:
  sensor:

SHT45 MQTT YAML

mqtt:
  sensor:
    - name: "Living Room SHT45 Temperature"
      state_topic: "home/livingroom/sht45"
      value_template: "{{ value_json.temperature }}"
      unit_of_measurement: "°C"

    - name: "Living Room SHT45 Humidity"
      state_topic: "home/livingroom/sht45"
      value_template: "{{ value_json.humidity }}"
      unit_of_measurement: "%"

    - name: "Living Room SHT45 Heater"
      state_topic: "home/livingroom/sht45"
      value_template: "{{ value_json.heater }}"
      unit_of_measurement: ""

HA now reads the JSON your ESP32 publishes.

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5. ESP32 Arduino Code for SHT45 (MQTT JSON Payload)

This publishes data in the exact structure your YAML expects.

#include <WiFi.h>
#include <PubSubClient.h>
#include <Adafruit_SHT4x.h>

#define WIFI_SSID "YOUR_WIFI"
#define WIFI_PASS "YOUR_PASSWORD"
#define MQTT_SERVER "192.168.0.10"

WiFiClient espClient;
PubSubClient client(espClient);
Adafruit_SHT4x sht4 = Adafruit_SHT4x();

void setup() {
  Serial.begin(115200);

  WiFi.begin(WIFI_SSID, WIFI_PASS);
  while (WiFi.status() != WL_CONNECTED) delay(500);

  client.setServer(MQTT_SERVER, 1883);

  if (!sht4.begin()) {
    Serial.println("SHT45 not found!");
    while (1);
  }
}

void loop() {
  if (!client.connected()) {
    while (!client.connected())
      client.connect("ESP32_SHT45");
  }

  sensors_event_t humidity, temp;
  sht4.getEvent(&humidity, &temp);

  String json = "{";
  json += "\"temperature\":" + String(temp.temperature) + ",";
  json += "\"humidity\":" + String(humidity.relative_humidity) + ",";
  json += "\"heater\":\"off\"";
  json += "}";

  client.publish("home/livingroom/sht45", json.c_str());

  client.loop();
  delay(5000);
}

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6. Adding the SHT45 to a Home Assistant Dashboard

Example Lovelace card:

type: vertical-stack
cards:
  - type: sensor
    entity: sensor.living_room_sht45_temperature

  - type: sensor
    entity: sensor.living_room_sht45_humidity

  - type: history-graph
    hours_to_show: 24
    entities:
      - sensor.living_room_sht45_temperature
      - sensor.living_room_sht45_humidity

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7. Optional Automations

Turn on AC if humidity exceeds 65%:

automation:
  - alias: "Dehumidify Living Room"
    trigger:
      - platform: numeric_state
        entity_id: sensor.living_room_sht45_humidity
        above: 65
    action:
      - service: climate.set_hvac_mode
        target:
          entity_id: climate.living_room
        data:
          hvac_mode: dry

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8. Troubleshooting

SHT45 not detected (ESPHome)

• Check 3.3V vs 5V
• Enable scan: true
• Sometimes swapping SDA/SCL fixes a bad cable

MQTT sensors not showing in Home Assistant

• Confirm MQTT server IP
• Confirm JSON is valid
• Check Home Assistant logs

Humidity too high or too low

• Longer update_interval: reduces self-heating

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9. SHT45 vs BME280 vs DHT22 Comparison

Sensor	Accuracy	Stability	Notes
SHT45	★★★★★	★★★★★	Most accurate consumer humidity sensor
BME280	★★★★☆	★★★☆☆	Good but humidity drifts over time
DHT22	★★☆☆☆	★★☆☆☆	Outdated, slow response

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