Aero module

In this chapter, we are setting up the Arduino module for the Aeroponics tote based on an Arduino Nano V3 and nRF24L01+ wireless transceiver. Optionally an Arduino RF-Nano could be used, where the wireless transceiver is already integrated.

The module is responsible for:

Timing the misting interval and duration by controlling the spray and bypass solenoids
Controlling the high-pressure pump, including priming the pump with the help of the bypass solenoid
Measuring tank pressure - The pump is controlled based on the reading
Measuring the weight of the tote - Shows the remaining nutrient solution
Processing commands from the Main module and reporting back
Keeping the plants alive even when the Main module goes down

Gbox420 sketch: Gbox420_Nano_Aero_Tank
SketchUp 3D Warehouse: Gbox420 - ShowRoom - Aero Tank tab
Or visit the Gbox420 GitHub page and download the entire project.

Table of contents

HX711 + 4 weight cells

Wireless transceiver

If you decide to use a different pin layout from what is shown below, update the Settings.h file. Look for variables ending with Pin

RF-Nano

Arduino RF-Nano has the nRF24L01 wireless transceiver already integrated. Here are a few test scripts you can run to make sure the wireless communication works:

Verify the Arduiono and nRF24L01+ connection

By updating the wireless transmission rate:

Test-WirelessConnection_Nano.ino

Expected test result: 'Data Rate' row should have changed from 1MBPS to 250KBPS

Relay data between two nRF24L01+ transceivers

You will need a second RF-Nano or an Arduino board with a nRF24L01+ transceiver for this test. Tests the two-way communication between a Transmitter and a Receiver by exchanging a set of pre-defined stuct (group of different data types) known by both parties. One device will initiate the communication (Transmitter) by passing the commandTemplate struct. When the Receiver gets this command, it returns it to the transmitter with a pre-cached responseTemplate struct. A maximum of 32bytes of data can be exchanged in one transmission.

Transmitter: Test-WirelessTransmitter.ino
Receiver: Test-WirelessReceiver.ino

Expected test result: Both devices printing the exchanged data to their serial outputs.

Relay multiple packets of data between two nRF24L01+ transceivers

When you need to transfer data larger than 32 bytes, it must be split into multiple transmissions. The transmitter will send multiple commands in a fixed order containing different pre-defined stucts known by both parties. When the Receiver gets this command it confirms it back to the transmitter with a pre-cached response and based on the current command's SequenceID it loads the next response into the ACK cache. Templates of the data exchanged: WirelessCommands_Test.h

Transmitter: Test-WirelessTransmitter_MultiPackets.ino
Receiver: Test-WirelessReceiver_MultiPackets.ino

Expected test result: Both devices printing the exchanged data to their serial outputs.

Rf-Nano

ATmega328P microcontroller integrated with NRF24L01 transceiver
32 KB flash8 analog pins14 digital pins (6 PWM)Datasheet
Amazon.com

Buzzer

When a module starts up or receives a command a piezoelectric buzzer provides audio feedback. To protect the buzzer from excess current make sure to have a minimum 200Ω resistor between the Arduino port and the + side of the buzzer. If you find the volume too loud use a larger resistor. I took a few sound intensity measurements using different resistance values: 220Ω - 71dB, 330Ω - 69dB, 1kΩ - 59dB, 3kΩ and above are inaudible.

+ pin: Arduino 2 (digital output). Connected through a resistor to limit current and volume: 200Ω(loud) - 1kΩ(quiet)

- pin: Arduino GND (Ground)

Test-Buzzer sketch

Expected test result: Plays the Star Wars theme song

Piezo buzzer

5V, 25 mA
Amazon.com

Metal film resistor

200 Ω - 1 kΩ , 0.25 W
Amazon.com

Bypass capacitors

Bypass capacitors or decoupling capacitors are added between each power and ground line to filter out noise from the power supply and make the entire circuit more stable. Here is an excellent video from EEVblog that explains bypass capacitors.

Be mindful that electrolytic capacitors are polarized, meaning they can only be connected one way in a circuit. The negative lead is generally marked on the capacitor with a bar or "-" symbol, connect this to Ground (or the more negative line). Do not mix up the polarity as this will heat up and destroy the capacitor in a few seconds. Ceramic capacitors have no polarity, they can be connected in any direction. The capacitance of both capacitors can be changed based on the power needs, as long they support a minimum of 16V voltage.

DC input 12V
2200 uF - 16V Electrolytic capacitor + pin: +12V DC

2200 uF - 16V Electrolytic capacitor - pin: Ground

0.1 uF - 50V Ceramic capacitor pin 1: +12V DC

0.1 uF - 50V Ceramic capacitor pin 2: Ground

DC step down output 7V
1000 uF - 16V Electrolytic capacitor + pin: DC step down Vo+ output

1000 uF - 16V Electrolytic capacitor - pin: Ground

0.1 uF - 50V Ceramic capacitor pin 1: DC step down Vo+ output

0.1 uF - 50V Ceramic capacitor pin 2: Ground

Arduino 5V

470 uF - 16V Electrolytic capacitor + pin: Arduino 5V

470 uF - 16V Electrolytic capacitor - pin: Ground

0.1 uF - 50V Ceramic capacitor pin 1: Arduino 5V

0.1 uF - 50V Ceramic capacitor pin 2: Ground

Arduino 3.3V
10 uF - 16V Electrolytic capacitor + pin: Arduino 3.3V
10 uF - 16V Electrolytic capacitor - pin: Ground
0.1 uF - 50V Ceramic capacitor pin 1: Arduino 3.3V
0.1 uF - 50V Ceramic capacitor pin 2: Ground

Electrolytic capacitor

470 - 2200 uF, 16 V or above
Amazon.com

Ceramic capacitor

0.1 - 100 uF, 16V or above rated
Amazon.com

DC-DC Buck Converter

To convert the 12V power input and feed the Arduino Nano a DC to DC step down power supply is used. These buck converters are cheap, power-efficient, have a small physical size, and support a wide range of DC input voltages. To adjust the output voltage you will need to have a multimeter tool to monitor the output voltage while changing the adjuster screw. Be careful: The Vin pin does not have a reverse polarity protection diode like the barrel jack, never mix up GND and Vo+ from the power supply!

VO+ pin: Arduino Vin. Adjusted to 7 volts.

GND pin: Arduino GND (Ground) + Power input ground (Common ground)

In+: Positive power input (12V)

EN pin: Not connected

DC-DC Buck Converter

Input voltage: DC 4.5 to 24VOutput voltage: Adjustable DC 0.8 to 17VOutput current: Max 3A
Amazon.com

Flyback diode

Turning off inductive loads like a solenoid, motor or a relay (anything that has a coil that creates a magnetic field) generates a harmful voltage spike. A flyback diode is used to re-circulate the current generated by the collapsing magnetic field through the load until it dissipates, protecting other components on the circuit from a high reverse voltage shock. Here you can find a highly recommended summary video of inductive spiking, explaining why it is crucial to have a flyback diode.

Flyback diodes are connected between the power lines as close to the inductive load as possible. The diode allows current to flow in only one direction indicated with a marking on one of its ends, current can only pass from the unmarked side to the marked side. Connect the marked side to the positive power line and the unmarked to the ground. During normal operation, no current will flow through the diode. When the power to the motor/relay is turned off their magnetic field will start collapsing and this force will continue pushing electrons. This is when the diode will start conducting and route the electrons back to the load, avoiding voltage build-up and sparks. Here is a much better explanation with pictures of the process.

Schottky diodes have low power consumption and support fast switching frequencies making them ideal flyback diodes for PWM- controlled motors. When selecting a diode check the following parameters:

blocking voltage: At least double of the voltage needed by the device it protects (e.g. Load 12V -> Diode 24V )
peak surge current: Higher than the maximum current the device it protects will use (e.g. Load 3A -> Diode 5A)

I have used the 1N5818 diode (30V blocking voltage, 25A peak surge current) between the power lines of the Spray solenoid, Bypass solenoid, and High-pressure pump.

Flyback diode connected across the Bypass solenoid's DC input

Flyback diode connected across the High-pressure Pump's DC input

Schottky diode

Minimum 25V blocking voltage, Min 4A peak surge current

Amazon.com, Amazon.de

Noise filter

Running motors generate electrical noise, this needs to be filtered using capacitors connected between:

Ground and motor housing
VCC and motor housing
Ground and VCC

Add the filter capacitors to the high-pressure pump motor. To find out more about this technique check out Pololu.

3 Noise filter capacitors + Flyback diode across motor terminals

Ceramic capacitor

For each motor: 3 x 0.1 uF , 16V or above rated

Amazon.com, Amazon.de

MOSFET DC Switch 5V

A solid-state MOSFET switch is used to control the pressure pump's speed. Solid-state switches can be turned on and off very fast, making them ideal to control the motor speed using a PWM signal generated by the Arduino.

This component is optional and can be replaced with a standard relay as long as the Speed and SpeedLowLimit are set to 100 in the Settings.h file to disable PWM.

In+ : Max 24V /10A DC power in
In- : Ground in
Out+ : DC power out
Out- : Ground out

VCC pin: Arduino 5V
GND pin: Arduino GND (Ground)
S pin: Arduino 3 (digital output with PWM support)

Test-TransistorRelayPWM

Expected test result: Starting from 0% the motor speed gradually increases to 100%, then decreases back to 0%. Note the point where the motor stalls and starts back again, update the SpeedLowLimit in the Settings.h file to a ~10% higher value to ensure not stalling the motor even at 0% motor speed.

MOSFET DC Switch 5V

5V power, Supports switching up to 24V - 30A DC

Amazon.com

Pressure sensor

This component is used to monitor the pressure in the pressure tank by providing an analog signal linearly changing with the pressure. As every sensor is different they need to be calibrated, for this, you need two values:

Offset: The measured voltage at 0 pressure. Use the test sketch from the bottom of this section to determine it and update the PressureSensorSettings - Offset value in the Settings.h file.

Formula used to calculate the offset: Offset = AnalogSensorReading at zero pressure * 5.0 / 1024.0

Ratio: How the sensor output voltage translates into pressure. This is a sensor-specific constant that is usually available in the sensor's specification. For the sensor used in this project, this is 2.7. Update the PressureSensorSettings - Ratio value in the Settings.h file if you use a sensor with a different ratio.

Formula used to calculate the pressure: Pressure = Ratio * ( (AnalogSensorReading * 5 / 1024) - Offset)

If you use a different sensor with an unknown voltage to pressure ratio and own a pressure gauge, you can use this Google Sheets - Pressure sensor calibration sheet to determine the voltage to pressure ratio.

Gbox420 - PressureSensor Calibration

Yellow wire: Arduino A7 (Analog input)
Black wire: Arduino GND (Ground)
Red wire: Arduino 5V

Test-PressureSensor sketch

Expected test result: At startup, the 0 pressure offset is measured for 5 seconds, then pressure readings are displayed every 5 seconds. Use the displayed Offset value to update the PressureSensorSettings - Offset value in the Settings.h file.

Pressure sensor

5V power, 1/4" external threadPressure range: 0 - 12 bar / 0 - 174 PSI

Amazon.com, Amazon.de

Relay modules

A two-channel relay module controls the bypass and spray solenoids. Single-channel relays tend to use positive logic, where: HIGH = relay ON, LOW = relay OFF. Multi-channel relays tend to use negative logic, where: HIGH = relay OFF, LOW = relay ON. You can find more details of how relays work at lastminuteengineers.com.

The default settings assume you are using a Negative logic relay for the solenoids. If you notice that your spray or bypass solenoid is ON most of the time and heats up, you need to edit the Settings.h file the following way:

Change the Version number to any other number to force an EEPROM update: static const uint8_t Version = 9;
Set the .BypassSolenoidNegativeLogic = false to use positive logic.

NC: Normally connected. When the relay is off or has no power this pin is connected to COM. When the relay is on this pin is not connected.
COM: Common. The incoming power cable connects here, based on the relay's state the power is directed to the NC or NO ports.
NO: Normally Open. When the relay is off or has no power this pin is not connected. When the relay is on this port is connected to COM.

2 channel relay

GND pin: Arduino GND (Ground)

In1 pin: Arduino 5 (digital output) - Spray solenoid

In2 pin: Arduino 4 (digital output) - Bypass solenoid

VCC pin: Arduino 5V

When a single relay is active it uses ~60 mA, when both relays are active the total power consumption is ~120 mA. This is still within the supported range of the 5V output on the Arduino Nano, where the 5V regulators are rated for 500mA.

Test-2ChannelRelay sketch

Expected test result: Turning both relays on with a 10-second delay. After 10 seconds turn off all relays, then turn on each relay on for 10 seconds individually.

Test-1ChannelRelay sketch

Expected test result: Turning on the relay for 10 seconds, then turning it off and waiting 10 seconds before restarting the cycle.

1 channel relay for pressure pump (Optional)

5V power, Supports switching up to 250V - 10A AC, 30V - 10A DC powerWhen no PWM pump speed control is needed

Amazon.com, Amazon.de

2 channel relay for Spray and Bypass solenoids

5V power, Supports switching up to 250V - 10A AC, 30V - 10A DC power

Amazon.com, Amazon.de

Weight sensor

The aeroponics tote sits on a weight platform that measures the weight of the remaining nutrient solution. Before using a weight sensor it needs to be calibrated using the sketch from the bottom of this section. The sketch will return two parameters that need to be written in the Aeroponics module's Setting.h file under WeightSensorSettings - Scale and Offset variables.

Offset: The raw reading when no weight is on the scale. The calibration sketch will automatically tare the scale to 0 when it starts up and display the offset value.
Scale: The offset adjusted raw reading is divided by the scale factor to get the weight of the item on the scale in the calibrated units (kg or lbs usually)

Weight sensor

GND pin: Arduino GND (Ground)

DT pin: Arduino A0 (digital input)

SCK pin: Arduino A1 (digital output)

VCC pin: Arduino 5V

Load cell

Red wire: Weight sensor E+

Black wire: Weight sensor E-

Grey wire: Weight sensor A-

Green wire: Weight sensor A+

Test-WeightSensor_Aero sketch

Follow this procedure to calibrate the weight sensor:

Find an object with a known weight and update the WeightSensor_CalibrationWeight variable in the test sketch. For example, I used a 2 kg dumbbell weight.
Upload the test sketch
Remove all weights from the scale and press the Reset button on the Arduino. This will restart the sketch and automatically tare the scale to 0.
Place the known weight on the scale and wait for a few calibration cycles to run (Runs every 10 seconds).
Once the calibrated reading matches the calibration weight send any Serial input using the Send button on top of the Serial Monitor, I sent "ok" in the test run shown below. The sketch will display the Offset and Scale calibration values for the scale.
In the Aeroponics module's Setting.h file under WeightSensorSettings update the Scale and Offset variables with the calibrated values:

7. (Optional) You can also update the test sketch Offset and Scale variables and change the CalibrationComplete variable to true. After uploading the sketch it will skip the calibration part and just show the current weight on the scale.

Expected calibration output:

HX711 + 4 weight cells

4 set (4x4 cells) Rated to 50kb / 110lbs

Requires soldering!

Amazon.com, Amazon.de

Wireless transceiver

To relay data between the Main module and all other modules nRF24L01+ wireless transceivers are used. The Main module always acts as a transmitter, all other modules are receivers. When a receiver gets a package from the Main module it sends back a pre-cached Acknowledgement package to report its current status. You can find a great in-depth overview of the wireless module at lastminuteengineers.com.

Specs

Power supply voltage: 1.9V to 3.6V (Use the Arduino's 3.3V pin to power the module, do not connect the VCC pin to 5V! )
I/O pins tolerate 5V logic (Arduino can directly communicate with the module)
Communicates over a 4 pin Serial Peripheral Interface (SPI)
Draws 12 mA during a transmit, 0.026 mA in standby, and 0.0009 mA at power down
Maximum 125 channels
Operates using 2.4 GHz frequency band
Maximum range: 100 meter / 330 feet outdoors with internal antenna, 1000 meter / 3300 feet with external antenna
Supported data rates: 250kbps (Largest range) / 1 Mbps / 2 Mbps (Fastest data transfer speed)

GND pin: Arduino GND (Ground)

VCC pin: Arduino 3.3V

CSN pin: Arduino 9 (digital output)

CE pin: Arduino 10 (digital output)

MOSI pin: Arduino 11 (digital output)

MISO pin: Arduino 12 (digital input)

SCK pin: Arduino 13 (digital output)

Test-WirelessConnection_Nano sketch

This sketch will verify the connectivity between the Arduino and the nRF24L01+ wireless transceiver.

Expected test result: Successful update of the "Data Rate" field

Test-WirelessReceiver sketch

This sketch will verify the nRF24L01+ wireless transceiver communication between an Arduino Mega as the Transmitter, and an Arduino Nano as a Receiver. Requires an Arduino Mega to be set up as a Transmitter, check out the Main module - Test-WirelessTransmitter sketch for more details on setting up the Transmitter.

Expected test result: Printing the received command from the Transmitter on the serial output and sending a response message back.