I am thinking about a feature which would help me a lot saving some energy but still reacting on sensor signals.
The idea is to use a DHT22 as a humidity sensor and switching a fan on in case that the humidity reaches a certain level. Additionally I would like to set the ESP into deep sleep to save some energy. The fan would be enabled just below 2% of its time so the ESP consumes "significant" ammount of power compared to the fan.
If I would just use the ESP with its GPIO (and FHEM to monitor and control the GPIO), it would be very easy and flexible althow it cannot go into deep sleep. But I can also live with less flexibility and use the built in rules to turn on the GPIO based on fixed levels (and just use FHEM to monitor). The only problem with deep sleep is that it also disables the outputs of the ESP in case it goes into deep sleep.
My idea now is to use an I2C port expander to store the output state of the fan. In this case, the ESP will send the new state to the port expander and can be sent to sleep mode. But this time the fan keeps the output state as set before. I know that the time the ESP is awake might be too short for FHEM (or any MQTT) to respond and set the port expander so I thought of using the rules to set the I2C port expander instead.
I want to try this the next days and keep you informed it this really works.
Do you have any feedback?
