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Four ready-to-flash sketches that run a small greenhouse on one Uno: a replacement commercial controller starts around 180 USD and still needs its own sensors.
Board
arduino:avr:uno
Parts you need (8)
Soil moisture probe signal
Relay IN for the pump
10k NTC divider midpoint
MOSFET gate for the fan
H-bridge IN1 (open)
H-bridge IN2 (close)
Tank float switch
Buzzer or lamp
Sketches in this pack (4)
SoilMoistureIrrigation
Water only when the probe reads dry, with a hard daily cap so a stuck probe cannot flood the bed.
Reads a resistive or capacitive probe on A0 and drives a relay on D7. The daily cap is the safety device most tutorials leave out.
Wiring
Pin
Mode
Connect to
A0
INPUT
Soil moisture probe signal
7
OUTPUT
Relay IN for the pump
Connect in this order
Soil moisture probe signal → A0
Relay IN for the pump → 7
Values you can change
Name
Value
Unit
DRY_THRESHOLD
620
raw ADC
PUMP_SECONDS
20
s
MAX_RUNS_PER_DAY
6
runs
ThermistorFanControl
Ramp a 12 V fan with PWM from a 10k NTC thermistor instead of switching it fully on and off.
Uses the Steinhart-Hart approximation on a voltage divider at A1 and writes PWM to D9. Hysteresis keeps the fan from chattering at the setpoint.
Wiring
Pin
Mode
Connect to
A1
INPUT
10k NTC divider midpoint
9
OUTPUT
MOSFET gate for the fan
Connect in this order
10k NTC divider midpoint → A1
MOSFET gate for the fan → 9
Values you can change
Name
Value
Unit
TARGET_C
26
C
FULL_SPEED_C
33
C
VentWindowTimer
Open and close a linear actuator on a daily schedule using millis, with an end-stop timeout so the motor never stalls.
Drives an H-bridge on D4 and D5. The timeout is what protects a cheap actuator when a limit switch fails.
Wiring
Pin
Mode
Connect to
4
OUTPUT
H-bridge IN1 (open)
5
OUTPUT
H-bridge IN2 (close)
Connect in this order
H-bridge IN1 (open) → 4
H-bridge IN2 (close) → 5
Values you can change
Name
Value
Unit
OPEN_AFTER_MIN
480
min from power-on
TRAVEL_SECONDS
18
s
LowWaterAlarm
Latch an alarm when the tank float opens, so a night-time dry run is still visible in the morning.
Float switch on D2 with INPUT_PULLUP and a buzzer on D8. The latch is the point: a momentary alarm you slept through tells you nothing.
Wiring
Pin
Mode
Connect to
2
INPUT_PULLUP
Tank float switch
8
OUTPUT
Buzzer or lamp
Connect in this order
Tank float switch → 2
Buzzer or lamp → 8
Values you can change
Name
Value
Unit
DEBOUNCE_MS
400
ms
Get the full version
Four ready-to-flash sketches that run a small greenhouse on one Uno: a replacement commercial controller starts around 180 USD and still needs its own sensors.
This page is the free working part. The full version is sent to your inbox.
A packaged greenhouse controller with the same four functions sells for 180-320 USD, sensors excluded.
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