RFLink sensor - how to determine when it received data for the last time

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1

Hi All,

I have some key temperature sensors that I use in my central heating automation.
I want to send a warning when any of those sensors haven’t sent its readings to HA in the last say, 10 minutes.

According to HA docs, it is useless to use last_updated attributed in my case, and there is no last_changed one as far as I can see.
RFLink sensor platform does not provide fire_event option as RFLink switch does.

Any other ideas?

2

Check out this template sensor:

Note however that sensor.date__time has changed to sensor.date_time in the last update.

3

Thanks for your reply.
The thing is that sensor relies upon last_updated attribute, which according to the documentation:

Time the state was written to the state machine. Note that writing the exact same state including attributes will not result in this field being updated.

In case of a temperature sensor, for example, its state won’t be updated as long as the temperature remains the same and we’ll get false positives.

Or I’m missing something?

4

Yes that false positive could definitely happen.

If you are willing to change sensors the ESPhome devices can send heartbeat and status messages.

5

Well, I use 433MHz sensors and Arduino MEGA with RFLink as a 433Mhz->MQTT gateway.
Not sure I’m ready to change my sensors.

The thing is rflink component receives and distributes events so it should be possible to listen to them, I just don’t know exactly how…

6

Here is a workaround idea, it’s a bit of a hack.
Create an automation which every 6 mins sets the sensor value to -1, this would be set back to the real temperature on the next reading. But if no reading is made, it will stay at -1.
Then have an automation triggered by the sensor going to -1, with the condition it sleeps for 4 mins before checking again to make sure it’s still -1.

This would then mean the automation would be true and could perform your action.

It would mean making sure your heating automation effectively ignores the -1 value, to avoid it turning on the heating every 6 mins regardless of the actual temperature.

7

Or depending on how sensitive your temperature sensor is, you could create an automation which triggers if the temperature does not change for 10-20 mins, if you can measure to parts of a degree then should mean plenty of thermal fluctuations to stop the automation running.

8

What service do you call to set a (read only?) sensor value?

9

It’s not read-only, just tested it

10

Well, I’d rather do it the following way:

  • get current value
  • set sensor’s value to current value + say, 0.5
  • set the original value

Is should kind of do the trick, but will create a lot of unnecessary jitter, not sure how well the heating component can cope with it.

Again, I hope there is a way to listen to the original rflink events and do the job in parallel without affecting the sensors themselves.

11

What service did you call to write to a sensor?

12

I just used Set state in developer tools (under the main menu)
A quick search reveals this

1 Like
13

I have taken a look at the code and this is what I have seen:

  • sensor devices can not fire events (as you have said):
    if self._should_fire_event and identify_event_type(event) == EVENT_KEY_COMMAND:
  • I believe that RFLink propagates events to HA:
    self.async_schedule_update_ha_state()

According to the documentation:

state.last_changed This is not updated when there are only updated attributes.

I see two approaches:

  1. extend a sensor with a custom component that can send and extra attribute with a random value. I believe that this will update state.last_updated but not state.last_changed
  2. Every time you check state.last_updated attribute modify one of the sensor attributes hoping that next sensor update will rewrite it and change the state.last_updated. For RFLink devices you don’t have many attributes to modify, maybe you can play around with the name attribute.

I have done a chick test with the developer tools adding a name attribute for one of my RFLink sensors. After a few time, name attribute disapears and state.last_updated attribute gets updated while the state.last_changed remains the same.

I hope it works for you.

14

By the way, this is not a RFLink sensor issue. This behavior is the ‘normal’ for HA.
You will see the same behavior for any sensor you have (hue, mitemp, yr_symbol, sun…)

15

Yes, that’s all correct.
I’m not that advanced and don’t know how to extend a sensor with a custom component - are you sure it will work with RFLink?
I don’t quite get how to modify sensor’s attributes - I can do it from UI, but don’t seem to find a way to do it from say, automation.

And what did you do exactly to add an attribute?

I recently noticed that it it is possible to register a listener (by creating a custom component?) to the event bus and be able to analyse any event, thought I might use that approach as a last resort… what do you think? As I said, have no experience with HA custom components development solar, but happy to learn :wink:

What do you mean?

16

Well, it should work with any device.

The same as you, modify it from UI.

I have not played with listeners, but it seems a good idea, although it may be a little complex to start with something like that. I don’t know.

BUT, I have seen that there is another attribute you can play with:

Maybe you can try it first.

I mean that this behavior (not updating last_updated attribute for devices) is not a RFLink issue. This is the ‘normal’ behavior for all sensors, so you should not look for a solution in RFLink devices, it is the normal behavior defined by Home Assistant.

Good luck.