DIY home automation almost-instant-response WIFI smart switch for < $16 with MQTT

Parts list: AC/DC 12V 15W 1.25A “LED light strip” power supply – $2.33 Mini-360 DC/DC step down converter 4.75V-23V to 1V-17V – $0.62 Cactus Micro (Rev2) – $12(Alternative: D1 mini NodeMCU – $3.73, but my instructions below are for Cactus Micro) Relay – $0.60 Total: $15.55 ($7.28 if you go with the mini NodeMCU) WARNING!!! […]