Wiring

Components

• 1x Arduino Uno R3
• 3x Water pump (12V)
• 3x MOSFET (N-Channel)
• 3x Resistor (10k Ohm)
• 3x Flyback diode
• Wires

Explanations

• Flyback diodes are needed, because the water pumps are inductive loads and can generate voltage spikes when turned off. The diodes are used to protect the MOSFETs from these spikes.
• The resistors are used to pull the gate of the MOSFET to ground when the Arduino is not driving the gate. This is to prevent the MOSFET from turning on when it should be off.

Open questions

• Can the pumps actually be powered by the same 12 V power supply?
  -> Yes they can, as long as the power supply can provide enough current for all pumps.
• What can be used to control the speed of the pumps?
  -> You can use PWM (Pulse Width Modulation) to control the speed of the pumps. However, be aware that the excess energy will be dissipated as heat.
• What can be used to measure the water level in the water tank?
  -> There are a lot of different options to measure the water level in a tank. Some of the most common are ultrasonic sensors, float switches and capacitive liquid level sensors. The best option will depend on the specifications of the water tank and the requirements of the project. Mostly a small float switch will be enough to detect the water level in the tank.

Hardware

Note

Some of the shops have different distributors for different countries. Please check the availability of the components in your country.

• Adafruit Distributors

Moisture Sensor

Option 1.1: Adafruit STEMMA Soil Sensor - I2C Capacitive Moisture Sensor - JST PH 2mm Eckstein/Adafruit + Kable Eckstein/Adafruit

Option 1.2: APKLVSR Capacitive Soil Moisture Sensor v1.2 Amazon

The sensor includes an on-board 3.3V voltage regulator, making it suitable for 3.3V and 5V MCUs. Plus, it consumes less than 5mA of current.
Note that this sensor can only provide a qualitative measurement of soil moisture. As the soil gets wetter, the output value decreases, and as it gets drier, the output value increases. When powered at 5V, the output ranges from about 1.5V (for wet soil) to 3V (for dry soil). Source

Test measures - Option 1.2

Air:

Type	Moisture Value 1	Moisture Value 2
In Water	11776	ToDo
At Air	27840	ToDo

Coconut fibre:

Type	Moisture Value 1	Moisture Value 2
Wet soil	15168	ToDo
Dry soil	22656	ToDo

Plant soil:

Type	Moisture Value 1	Moisture Value 2
Wet soil	16064	ToDo
Dry soil	ToDo	ToDo

MOSFET

FET STP60NF10, N-Channel, 100V, TO-220 Pollin.de

Key Specifications of STP60NF10:

• VDS (Drain-Source Voltage): 100V
  This is much more than you need for your 12V circuit, so it provides a good safety margin.

• ID (Continuous Drain Current): 80A
  This is far more than you need for your small water pumps. Having such a high current rating means the MOSFET will easily handle the startup surge of the pumps without overheating.

• Rds(on) (On-State Resistance): 0.019Ω
  This is very low, meaning the MOSFET will have minimal resistance when it's on, leading to less heat and higher efficiency, especially when switching at high currents.

• Package: TO-220
  The TO-220 package is common in power electronics and easy to work with for heatsinking if you need to dissipate any heat, but with your pump's lower current draw, you may not even need a heatsink.

Pumps

Note

The selection of the appropriate pump - be it a centrifugal pump, submersible pump, or self-priming pump - depends on it's planed installation location. Each type of pump has distinct requirements regarding the positioning of the tank and whether the hoses need to be primed with liquid. For instance a centrifugal pump needs to be primed with liquid before it can start pumping, while a submersible pump can be placed directly in the water.

Centrifugal Pump

Option 2.1: Water pump 8-12 V-, 1,5 l/min. Pollin.de

Option 2.2: Water pump 12 V-, 10 l/min. Pollin.de

Flyback Diode

Important

Please be aware that depending on the pump you choose, you may need to adjust the flyback diode to match the pump's current rating.

For Option 2.1 Pumps: 1N5819 Pollin.de

For Option 2.2 Pumps: 1N5822 Pollin.de

Power Supply (12V)

SHNITPWR 12V Power Supply AC 100V ~ 240V to DC 12V 10A 120W Amazon

This should be enough for both pump options.

• For 6x Option 2.1 pumps, the total current draw is only 2.1A ( 6 × 350mA = 2.1A), which is well within the 6.25A capability of this power supply.
• For 3x Option 2.2 pumps, the total current draw is 5.4A (3 × 1.8A = 5.4A), also safely within the power supply’s capacity.

Ultrasonic Sensors

Fdit 5V water proof ultrasonic sensor (Fdith9obv7uqge) Amazon