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History Graph question

Hello people,
I am using blynk for a communication between my MEGA + ESP8266 + sensor, and I have some question about using it.
I want it in the blynk application (already created with a button + sensor reading) to see a history of the sensor values. I have read that the necessary widget would be History Graph, but I am not clear on how this works.
Is it necessary for History Graph to save the data (txt, or csv …) in an SD in order to read it, or save it in the CLOUD SERVER?

I read:
http://docs.blynkapi.apiary.io/#reference/0/pin-history-data/get-all-history-data-for-specific-pin
but I am not clear its use, could you put an example of it ?? (I’m going to pay for more energy but before I would like to know how exactly it works)

Thank you!!!

http://docs.blynk.cc/#widgets-displays-history-graph

The data is already there (on the server) so all you need to do is load the widget and view it.

it means that it is not necessary to program arduino to save data in txt or csv, right?

Yup :wink:

As long as these requirements are met of course (as per the docs)…

In order to see data in history graph you need to use either widgets with “Frequency reading” interval (in that case your app should be open and running) or you can use Blynk.virtualWrite on hardware side. Every Blynk.virtualWrite command is stored on server automatically. In that case you don’t need application to be up and running.

thank you very much, I will buy energy and try it
regards

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