Solar watering system with Arduino (ESP8266) and a 9V water pump.
Plants are very happy with it.

Supplies

Arduino C++ sketch running on an ESP8266EX D1 Mini from Lolin running at 80MHzRaspberry + Home Assistant for Web GUI, automations and MQTT server
88x142 5V solar panel
Sony VCT6 18650 Lithium Battery
TP4056 protected lithium charger
MT3608 DC DC step up module to step up battery voltage @ 5.5V, ESP chip is happy with it
MT3608 DC DC step up module to step up battery voltage @ 8.66V, water pump is powerful with it
Relay Shield to safely power the water pump and "detach it from the circuit"
(100kΩ + (22kΩ + 4.4kΩ)) voltage divider for Battery voltage level monitoring circuit
3.5V/9V water pump (3W @ 9V)
TTP223 capacitive touch button with A contact soldered (HIGH signal when button is not pressed, LOW signal when button is pressed), used to reset the microcontroller
Google Home Mini for Voice Recognition