Relay + pump

The relay + pump kit is a high-trigger relay module with a water pump connected through its contacts, both powered from the same 5 V feed. It costs $18 and is for watering automatically: a plant loop that reads soil moisture and pumps when dry. Wire vcc to 5 V, gnd to ground and sig to a GPIO — sig high starts the pump.

What's inside

Part	Qty	Price each
Relay module	1	$4
Water pump	1	$8
Total	2	$12

The relay module switches the pump's current from the 5 V rail; the GPIO only drives its ~2.5 mA input stage.
The pump is the load; in the simulator it waters the soil in its zone while running, and moisture sensors there see it.

Exposed pin	Inside the kit
vcc	`relay:DC+`
gnd	`relay:DC-`
sig	`relay:IN`

vcc feeds the relay coil and the switched loop (DC+ → COM → NO → pump+ → pump− → DC−), so it must be 5 V. sig is high-trigger and needs only a logic-level high from a GPIO. The kit has no chain ends.

Wiring it in circuit.py

circuit.py

from wiring import *

pi = Pi()
water = kits.RelayPump()

pi.V5 >> water.vcc       # relay coil and switched supply are both 5 V
water.gnd >> pi.GND
pi.GPIO17 >> water.sig   # high = pumping

Driving it in main.py

main.py

from gpiozero import OutputDevice
from time import sleep

pump = OutputDevice(17, active_high=True, initial_value=False)

while True:
    pump.on()
    sleep(1)
    pump.off()
    sleep(1)

Why buy the kit

Loose parts cost $4 + $8 = $12.00, against $18 — $6.00 for the four-wire switched loop done and tested. A pump is a motor, so it is exactly what must not be wired to a GPIO directly; the kit's relay is the isolation, and the relays primer explains the contacts if you want to do the wiring yourself.

Simulator vs real hardware

Contacts follow the input with the modelled delays (about 10 ms on, 5 ms off), so short pulses still switch the pump.
On the board the pump is a 5 V, 100 mA stand-in; in its zone it waters the soil, and about 10 ml raises a 1-litre pot's moisture by one percentage point, so a real control loop — read soil moisture, pump, read again — closes.
A relay cannot vary pump speed: on/off is all it does, and rapid PWM switching would buzz and wear the contacts.