Very little experience with programming and electronics but I need help with writing a program that would send data from RuuviTag in the same format as the firmware to gateway and then change the program so the temperature comes from an external temperature sensor. I hope this makes sense.
If you are building on top of Ruuvi Firmware, you need to add a support to the external sensor and then define it as the first priority temperature sensor. Which sensor you are using and how do you plan to connect it?
RuuviTag is no longer officially supported by Espruino, but RuuviTag will probably run same firmware as any generic Espruino board on nRF52. You might need a wired connection to upload the firmware to RuuviTag.
If your RuuviTag board version is B8 the sensors are powered off by default by GPIO, so low-power operation should be doable. After soldering the sensor to test points under board you need to read the sensor with Espruino code and then format the advertisements according to Ruuvi data format.
Once you have the data in place Ruuvi Gateway should pick the data and deliver the data to Ruuvi Cloud, and then you can use the data in Cloud with your Ruuvi Cloud subscription.
Yes I have actually talked with Jari about this project. And my question was derived from his suggestions on how to do this. The biggest issue for me would be with the programming since I have no experience in that and not a lot of time to learn.