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.

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

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

DC step down power supply

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

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 Hempy bucket pumps.

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 both Hempy pump motors. You can find out more about this technique on Pololu.

Transistor DC Relay

Two solid-state MOSFET relays are used to control the speed of the watering pumps. 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.