The HomeKit temperature and humidity sensors have a number of common options and are grouped here.

The following configuration is available for garage doors:

{
  "c": { "l": 13 },
  "a": [{
    "t": 1,
    "0": { "r": [{ "g": 12, "v": 0  }] },
    "1": { "r": [{ "g": 12, "v": 1 }] },
    "b": [{ "g": 0 }],
    "s": 5
  }, {
    "t": 24,
    "g": 14,
    "n": 4,
    "j": 30,
    "z": -0.8
  }]
}

This is an example of a Sonoff TH10 unit with a temperature & humidity sensor connected to GPIO 14 and an LED connected to GPIO 13 ("l": 13). The device also has a switch output ("t": 1) connected to GPIO 12 with actions "0" & "1". The switch has a button connected to GPIO 0 ("b": [{ "g": 0 }]).

A second accessory, the temperature & humidity sensor accessory ("t": 24) is attached to GPIO 14 ("g": 14) and is a Si7021 sensor ("n": 4). The polling time has been set to 30 seconds ("j": 30) and to improve the accuracy of the reading an offset of -0.8ºC is applied ("z": -0.8). No offset is being applied to the humidity sensor.

NOTE: The following options are not needed in this example as they are the default options but are included to make the example more readable: "t": 1, "v": 0 & "j": 30

Temperature and humidity sensors only have one action.

Sensor GPIO is defined by the "g" key contained within the accessory object.

Home Accessory Architect only supports one-wire temperature and humidity sensors. This is a mandatory option that specifies the GPIO the sensor is connected to.

NOTE: When specifying a thermistor sensor type the value of "g" will be ignored.

Sensor type is defined by the "n" key contained within the accessory object.

A variety of one-wire sensors are available and supported by HAA.

Sensor type 3 can only be used with device type 22 (Temperature Sensor), but sensor types 1, 2 & 4 can be used with any device type as they contain both a temperature sensor and a humidity sensor.

Datasheet: DHT11

The DHT11 sensor is a good value temperature & humidity sensor giving a ±2ºC temperature accuracy and a ±5%RH humidity accuracy. It is one of the most common sensors used in Smart Devices.

Datasheet: DHT22

The DHT22 sensor seems to be available in two forms; a new type branded as a Sonoff product and older types branded as ASAIR and other names. The older types should be configured as DHT22 Type 1 "n": 2 and the newer Sonoff branded type should be configured as a Si7021 "n": 4.

Datasheet: DS18B20

The DS18B20 sensor is capable of measuring temperatures from -55ºC to +125ºC (-67ºF to +257ºF) and has an accuracy of ±0.5ºC. It is available for Sonoff TH10/TH16 devices.

Datasheet: Si7021

The Si7021 sensor chip is an I²C device. The Sonoff branded sensor has a Si7021 sensor and an 8-bit MCU combined. The MCU translates the I²C commands into a 1-bit interface suitable for one-wire communication.

NOTE: The Si7021 sensor contains an integrated resistive heating element that can be used to drive off condensation. The data sheet recommends enabling the heater when the humidity readings are >80% as above this the sensor readings can become unreliable. This feature is not currently supported.

Bear this in mind if you are intending to use this sensor outdoors.

Thermistors (thermal resistors) are temperature dependent variable resistors. There are two types of thermistors, Negative Temperature Coefficient (NTC) "n":5 and Positive Temperature Coefficient (PTC) "n":6. When the temperature increases, PTC thermistor resistance will increase and NTC thermistor resistance will decrease. They exhibit the opposite response when the temperature decreases.

HAA assumes the thermistor is connected to the ADC pin on the ESP8266 MCU.

Sensor types 5 & 6 assume that the device is using a standard 10K Ohm thermistor and the temperature is calculated in ºC from the ADC value. Sensor types 7 & 8 return the raw ADC value (see note on humidity offset) for a way to reduce the raw ADC value so that it can be viewed within HomeKit.

Sensor polling time is defined by the "j" key contained within the accessory object.

A temperature and/or humidity sensor is polled on a regular basis to read the latest values. These values are then posted to HomeKit. If this option is not specified then the sensor will be polled once every 30 seconds.

Temperature offset is defined by the "z" key contained within the accessory object.

NOTE: This option is NOT available for device type 23

The accuracy of the available one-wire sensors varies and may sometimes read consistently higher or lower than the actual temperature. The temperature offset option enables calibration of the sensor by specifying a positive or negative offset to apply to the reading.

The option uses is a floating point value, accurate to 1 decimal place e.g. 1.1

Humidity offset is defined by the "h" key contained within the accessory object.

The accuracy of the available one-wire sensors varies and may sometimes read consistently higher or lower than the actual humidity. The humidity offset option enables calibration of the sensor by specifying a positive or negative offset to apply to the reading.

The option uses is a floating point value, accurate to 1 decimal place e.g. 1.1

NOTE: The humidity offset can be used with a temperature sensor ("t":22) in conjunction with thermistor types "n":5,"n":6,"n":7 & "n":8. The temperature value will then be multiplied by the humidity offset value e.g.

{
  "c": { "l": 13 },
  "a": [{
    "t": 22,
    "n": 8,
    "h": 0.1,
    "j": 10
  }]
}

In this example the raw ADC value returned from the PTC thermistor is multiplied by 0.1 before being returned to HomeKit. This can be used to overcome the maximum value a HomeKit temperature sensor can report i.e. 200ºC.

Wildcard Actions "y[n]" are supported by this accessory. The supported list is:

Refer to Wildcard Actions for more detail.