“The ultra low power weather station
For some time I have been fascinated by the possibilities of the ESP8266, but I never really considered it good for a life on batteries. I got an idea of making an outdoor weather station that would send measured light level, temperature and humidity to my home automation server.
The ESP is a hungry beast when it’s doing WiFi. According to different sources on the internet it uses about 70 mA on average when WiFi is on! This would mean that I have to change batteries on my sensor quite some times every year.
I instead came up with the idea of a design using an AtTiny85 for doing frequent measurements and then once in a while to wake up the ESP beast to transmit it’s recorded data to the server.” - Link