Derivative?

ESPHome
1

To extract a derivative of a sensor (or even simply delta), is it best to create a global variable to store previous value and compare with current value? Is there a better method?

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3

For a delta sensor, if you need to do it in ESPHome you can put this on a copy sensor:

filters:
  - lambda: |-
      static float last_value = 0;
      float change = 0;
      change = x - last_value;
      last_value = x;
      return change;

And on ESPHome Discord if you search for “Delta Sensor (Change from previous value). Survive Deep Sleep” there’s also a way using globals that will survive a deep sleep.

4

I didn’t realize that’s how the static keyword works in lambdas. Nice. That solves the issue.

Just out of curiosity; how can I use a copy sensor to get delta? Do I understand correctly that it simply mirrors the state of another?

EDIT: right, I think I get it: instead of creating a separate sensor that fetches the value of the other sensor, it’s easier to create a copy sensor for the delta purpose.

1 Like
5

Copy sensors are a newer thing. Before that you’d probably use a template sensor to duplicate an existing one.

Most of the solution came from somewhere else on the internet with a few additional improvements then suggested by jesserockz on Discord.