Pin	GPIO	Desc							Usage
----------------------------------------------------------------------
D3	GPIO0	IO, 10k Pull-up					left Button (+)
D4	GPIO2	IO, 10k Pull-up, BUILTIN_LED	middle Button (-)
D5	GPIO14	IO, SCK							right Button (Mode)
D7	GPIO13	IO, MOSI						DHT22 Temp/Hum sensor
D0	GPIO16	IO								relay output, control heating
D2	GPIO4	IO, SDA							I2C SDA
D1	GPIO5	IO, SCL							I2C SCL
D6	GPIO12	IO, MISO						PIR sensor

D8	GPIO15	10k Pull-down, SS				-- unused --


Hardware via I2C:
LCD 1602	0x27
