Connect a button to a pin connected to a physical LED and you can turn the LED on and off. ... Nodemcu, temp/humidity sensor and the blynk app will display graphs over a user selectable range.

If Blynk goes under, he finds another service or rolls his own. In the meantime, he’s up and running without slogging through writing a lot of display code. I don’t see a problem.

Blynk is on Kickstarter now seeking $10,000 and has raised over $15,000 with 18 days to go. A pledge of $5 will get you the basic Blynk app for Android when it his Google Play.