Automatic plant watering

Parts in this circuit

Wiring, pin by pin

Red = 5 V, orange = 3.3 V, black = GND, other colours = signals. “Pin” is the position on the 40-pin header; the GPIO number is what the code uses. Power the Pi from a 5.1 V supply and wire with the power off.

Python code (gpiozero)

from gpiozero import MCP3008, OutputDevice, LED
from time import sleep

soil = MCP3008(channel=0)               # 0 = bone dry, 1 = soaking wet (simplified)
pump = OutputDevice(17, active_high=False)
warn = LED(22)

DRY_BELOW = 0.30

while True:
    moisture = soil.value
    print("Soil moisture:", round(moisture * 100), "%")
    if moisture < DRY_BELOW:
        warn.on()
        print("Too dry: pump ON for 3 seconds")
        pump.on()
        sleep(3)
        pump.off()
        print("Waiting for the water to soak in...")
        sleep(5)
    else:
        warn.off()
        sleep(1)

How the code works

• The probe gives a voltage that follows the water in the soil. The MCP3008 turns it into a number from 0 to 1.
• When the value falls below DRY_BELOW, the pump runs for exactly 3 seconds. Never leave a pump on until the soil reads wet: water takes time to reach the probe.
• The wait of 5 seconds after watering gives the soil time to soak. Without it the Pi would water again and flood the pot.

Parts to buy

The links open a search on each store, so you see what is in stock today. Check the model, voltage and price before you order.