BrewTemp is a controlled temperature PID with two temperature sensors, one for fermentation chamber, normally an old fridge or freezer and the other one inside of fermentation vessel by means of a thermowell.
This is not other temperature PID, the main goal is to control beer fermentation temperature remotely. I brew in a small village without internet directly, and in this case I use an old smart phone as WiFi router.
As an active actuation mechanisms, freezer or fridge used as chamber acts as cooling system. For heating actuation, a silicone heating cable and/or terrarium carpet around or below of fermentation vessel provides a temperature increment when is needed to maintain/reach temperature goal.
All captured or correlated data is sent to Ubidots (IoT platform) to be stored and represented graphically. Control variables as temperature objective can be modified from Ubidots. Other control is "mode", 0-StandBy, 1-Only Heat, 2-Only Cool and 3-Both Heat and Cool. Ramphour control allows to us to specify a time (hours) to reach the specified temperature goal, in one word, heat or cool slowly.
No any external controls, only a reset button to restart brewtemp.
External BrewTemp container, one 220v VAC to continuous supply(center). Up-right for heating and Down-right for cooling.
BrewTemp software is executed in a ESP8266 (Wemos D1 mini).
A true example as it works.