Backup sensor if unavailable?

ESPHome
1

I use this displaying my outside temp on a nextion display

  - platform: homeassistant   # outside temperature
    id: temperature_outside
    entity_id: sensor.ute_temperature
    accuracy_decimals: 0
    internal: true
    on_value:
       then:
          - lambda: 'id(nextiondisplay).set_component_text_printf("outtemp","%3.0f",id(temperature_outside).state);'

This is a Zigbee temp sensor connected to my HA server.
Sometimes this sensor is unavailable.
Is it possible with a if unavailable, get values from another sensor in home assistant?

  - platform: homeassistant   # outside temperature
    id: temperature_outside_1
    if temperature_outside_1 is unavailable
    use temperature_outside_2
    entity_id: sensor.ute_temperature
    accuracy_decimals: 0
    internal: true

Is this possible?

2

Add 2 homeassistant sensors in your esphome, one for temperature_outside_1 and another one for temperature_outside_2. Create a template sensor, use the lambda to select the sensor value based on its state.

3

Do you have an example, how the template should look like?

4

Something like this should work, though depends how your sensor behaves when it’s in unavailable state.

- platform: template
  name: Consolidated temperature Outside
  lambda: |-
    return !isnan(id(temperature_outside_1).state) 
      ? id(temperature_outside_1).state
      : id(temperature_outside_2).state;

It reads the state of first sensor, when it’s NaN (Not A Number) it’ll will use the reading from the second sensor.

5

Thank you.
It works like I hoped.
Is it easy to do the same if the value is older than 3 hours? Sometimes it takes a while before it is discovered af unavailable.

6

Believe that you can use a combination of sensors and sensor filters to achieve that. Personally I prefer a customer lambda expression which could be something like this:

- platform: template
  name: Consolidated temperature Outside
  lambda: |-
    const unsigned long threeHoursInMs = 3 * 60 * 60 * 1000;
    static unsigned long lastTempUpdate = millis();
    static float lastTempValue = NAN;
    if (isnan(id(temperature_outside_1).state)) {
      return id(temperature_outside_2).state;
    } else if (id(temperature_outside_1).state != lastTempValue) {
      lastTempUpdate = millis();
      lastTempValue = id(temperature_outside_1).state;        
    } else if (millis() - lastTempUpdate > threeHoursInMs) {
      return id(temperature_outside_2).state;
    }
    return lastTempValue;

What it does is: it stores the current tick count in a static var. Upon updating the sensor it checks if the state of temperature 1 is NAN, if so will immediately return temperature 2 value. Otherwise, when value is different than the stored value (initially set to NAN) then it stores the new value and updates the tick count. When last change was more than 3 hours ago, will also return temperature 2 value but when less than 3 hours, will return temperature 1 (= last known value).

Disclaimer: haven’t tried/tested this, it should work in theory… Let us know if this works.

7

This seems to work fine. Thank you again. :smiley: