SHT20 Element

The SHT2x sensors provide some high precision temperature and humidity sensors that communicate on the I2C bus.

In contrast to other sensors like DHT20 and Dallas no proprietary protocol on the wire is used as data is exchanged over I2C.

parameter	range
Supply voltage	DC : 2.1 - 3.6 V
Measuring range (humidity)	0 ~ 100 % RH
Measuring range (temperature)	-40 ~ +125 °C
Humidity accuracy	± 3 % RH
Temperature accuracy	± 0.3 °C
Resolution	Temperature: 0.04°C, Humidity: 0.01 % RH
Response time	Temperature: 5 - 30 s, Humidity: 8 s
Interface	i2c signal
i2c address	0x40

SHT40 is replacement offering some faster response times and better accuracy.

There are different housings and boards for the sensor available.

SHT20 Sensor

Web UI for the SHT20 Element

There is a card for this element available that shows the actual temperature and humidity.

SHT20 Sensor UI

Using the SHT20 Element

The SHT20 Element is not part of the core set of elements because it is not used very frequently. It can be registered and added to the firmware by including the definition of HOMEDING_INCLUDE_SHT20 in the sketch:

#define HOMEDING_INCLUDE_SHT20

This element requires no extra library and the calculation for temperature and humidity from the raw values is included in the element implementation.

Element Configuration

The following properties are available for configuration of the element:

address - The i2c address of the sensor. The default value is 0x40.

onTemperature - These actions are emitted by the element when the temperature gets a new value. The action will not be sent when reading the sensor values that stay the same.

onHumidity - These actions are emitted by the element when the humidity gets a new value. The action will not be sent when reading ne sensor values that stay the same.

From the base Sensor Element implementation the following properties are available for configuration:

readTime – Time between 2 probes being fetched from the sensor. Default value is 1m.

resendTime – The current values of the probe are resent after this specified time even when not changing.

warmupTime – This time is waited after powering the sensor on the first start or after a reset before the first data is fetched. The default time is set to 3 seconds.

restart – This property can be set to true to enable an automated restart when the sensor was not responding data.

From the base element implementation the following properties are available for configuration:

title – Caption text for the element. Used by the element specific cards on the dash boards.

description – A line of text that gives a short description of the device used in the web UI.

room – The location of the device.

loglevel – This property holds the element specific log level. The default value is LOGGER_LEVEL_ERR == 1.

startup – This property can be used to start the element using a different initialization phase. Possible values are “sys”, “net”, “time”. See The Startup sequence.

Configuration Example

This example shows how to configure this element:

{
  "sht20": {
    "0": {
      "description": "SHT20 Sensor",
      "address": "0x40",
      "onTemperature": "device/0?log=temp: $v\u00dfC",
      "onHumidity": "device/0?log=hum: $v%"
    }
  }
}

Element State

The following properties are available with the current values at runtime

active - Is set to true when the element is active.

temperature - The last read temperature value from the sensor.

humidity - The last read humidity value from the sensor.

Example State

{
  "sht20/0": {
    "active":"true",
    "temperature":"19.92",
    "humidity":"53.4"
  }
}