Hardware Setup

Hardware Setup

Sensor Module

The sensor module is designed with the following key features:

• Low Power Consumption: The module is optimized to consume as little power as possible, enabling long-term operation.

• Battery-Powered: It operates on a battery, ensuring independence from external power sources.

• Self-Replenishing Power: The module includes a mechanism to recharge its battery, reducing the need for manual intervention.

• Minimal Maintenance: Once deployed, the module is intended to function with minimal human intervention.

Components Required

• Arduino Pro Mini 3.3V 8MHz board x 1 (Rs.950)
• DHT11 temperature and humidity sensor x 1 (Rs.230)
• BH1750FVI light intensity sensor x 1 (Rs.450)
• 2N7000 MOSFET x 1 (Rs.20)
• 1M ohm resistors x 2 (Rs.10)
• LiPo battery (<1000mAh) x 1 (Rs.1500)
• CN3065 solar charger module x 1 (Rs.400)
• 6V 1W mini solar panel x 1 (Rs.400)
• MCP1700T-3302E/TT voltage regulator x 1 (Rs.230)
• 1uF ceramic capacitors x 2 (Rs.4)
• LoRa Ra-02 module x 1 (Rs.1450)
• Perforated board (dot board) x 1 (Rs.200)
• Wires in 4 colors (Rs.200)
• Female pin header bars x 2 (Rs.50)
• TTL converter (Rs.420)
• USB Mini cable (Rs.100)

Costs as of 2024 in Sri Lanka

Design Considerations

The Arduino Pro Mini 3.3V 8MHz development board is an ideal choice for this project due to its minimal component set, which reduces unnecessary power consumption. However, it does have two significant power-consuming components: the onboard voltage regulator and the power LED.

• Onboard Voltage Regulator and Power LED: The onboard voltage regulator has a quiescent current rating that impacts overall power efficiency. To optimize power usage, both the voltage regulator and the power LED should be physically removed from the board.

• Replacement Voltage Regulator: After removing the onboard regulator, the MCP1700T-3302E/TT low dropout (LDO) voltage regulator is used. This regulator has a low quiescent current, making it more efficient for battery-powered applications. The LDO is stabilized with 1uF ceramic capacitors across its input and output.

Sensor Connections

• DHT11: This temperature and humidity sensor is connected to 3.3V, GND, and GPIO 8 of the Arduino Pro Mini.

• BH1750: The light intensity sensor is wired to 3.3V, GND, and the I2C pins of the Arduino Pro Mini.

Power Management

• Solar Power: A 6V solar panel is paired with a CN3065 solar charger module to charge the LiPo battery, ensuring continuous operation even in remote locations.

• Battery Monitoring: Two 1M ohm resistors form a voltage divider to measure the battery level. High resistance values are used to minimize current leakage through the divider.

• Power Control: A 2N7000 MOSFET is used to disconnect power to the soil moisture sensor when readings are not being taken. This prevents unnecessary current draw when the microcontroller is in sleep mode.

Assembly Notes

• The CN3065 solar charging module is connected between the solar panel and the battery, with the battery directly powering the rest of the circuit.

• Screw terminals are used for secure connections between the wires from the sensors and the circuit board.

• Measure the total current draw from the battery to ensure proper power efficiency. A properly built sensor module should only draw around 10uA of current when it is asleep.

Using PCB

• For an easier build, The PCB version of the Apocalypse Sensor Module is available in our repo.

• Refer the PCB_Instructions for instructions on how to get the PCB manufactured.

• Placements and values of all components that should go on the PCB is marked.

• Solder all components into the placements marked on the PCB

• The CN3065 solar charging module is connected between the solar panel and the battery, with the battery directly powering the rest of the circuit.

• Screw terminals are used for secure connections between the wires from the sensors and the circuit board.

• J1 is a jumper for disconnecting power from the rest of the circuit. Solder two male pin headers in this place. This can be used as on/off switch during installations.

PCB wiring diagram

Sensor Module Enclosure

The sensor module must be housed in an enclosure designed to withstand environmental conditions and ensure the protection of internal components. The enclosure should have the following properties:

• Waterproof: Able to withstand heavy rains.
• Heat Resistant: Capable of enduring scorching sun.
• Durable: Robust and built to last.
• Simple Construction: Made from readily available materials and requiring minimal tools.

Hence the enclosure was built using the below material which are easily findable in any local hardware.

• 3.5" diameter 1 ft long PVC downpipe (Rs.220)
• 3.5" PVC end cap for the downpipe (Rs.150)
• 3.5" to 2" reducing socket (Rs.250)
• 2" diameter 2 ft long PVC pipe (Rs.100)
• 11" x 3.5" rectangular piece of plywood (Rs.50)
• Zip ties (Rs.20)

Costs as of 2024 in Sri Lanka

Preparing the Cap

PVC End Cap:

• The 3.5" PVC end cap will serve as the removable lid of the enclosure, allowing easy access to the internal components.
• Drill a small hole in the cap to accommodate the wires for the dome-shaped light intensity sensor.
• Mount the light intensity sensor on the cap by securing it with hot glue, ensuring there are no gaps between the sensor and the end cap to maintain waterproofing.

Preparing the Plywood Piece

Mounting the Circuit Board:

• The 11" x 3.5" plywood piece will act as a rigid structure for mounting the circuit board.
• Drill small holes in the plywood and the circuit board to secure them using zip ties.
• Drill additional holes to secure the battery and charging circuit.
• Use zip ties to fasten the battery and charging circuit to the plywood. AVOID DRILLING HOLES IN THE BATTERY OR DAMAGING IT IN ANY WAY.

Preparing the Stand

PVC Pipe Stand:

• Use the 2" PVC pipe as the stand.
• Measure and mark 2" from one end of the pipe, then mark 5 levels with approximately 1" gaps between each level.
• Drill 4 holes at each marked level (each hole approximately 4 mm in diameter) to ensure proper airflow through the DHT11 sensor for accurate humidity and temperature measurements

Preparing the Body

1. The 3.5" to 2" reduction socket is fitted to the 3.5" pipe.
2. Use hot glue to seal any gaps at this joint to waterproof the setup.

Assembly

1. Insert the Circuit Board:

   • Insert the plywood piece with the attached circuit board into the main body of the enclosure.
   • Ensure that the sensor wires and other components are properly routed through the body.

2. Mount the Stand:

   • Attach the stand to the bottom of the enclosure, ensuring that it raises the enclosure above the ground and protects the sensors from rain splashes.

3. Final Checks:

   • Verify that all components are securely mounted and that there are no gaps where water could enter.
   • Ensure that the enclosure is robust and well-sealed to protect the internal components from the elements.

Receiver Device

The receiver device is designed with the following key features:

• Continuous Operation: It runs 24/7, constantly listening for incoming messages from the sensor modules.
• Accurate Timekeeping: The device includes a real-time clock (RTC) to accurately timestamp the received data.
• Data Storage: It stores all incoming data securely for future access and processing.
• BLE Communication: The device is equipped with Bluetooth Low Energy (BLE) to enable wireless communication with a mobile application.
• Sufficient Processing Power: The receiver is powerful enough to manage concurrent processes, including data reception, storage, and BLE communication.

Components Required

• ESP32 Dev Kit V1 with an SPI flash of more than 4MB x 1 (Rs.1400)
• LoRa Ra-02 module x 1 (Rs.1450)
• DS1307 RTC module x 1 (Rs.230)
• Perforated board (dot board) x 1 (Rs.200)
• Female pin header bars x 2 (Rs.50)
• Wires in 4 colors (Rs.100)
• Power adapter with MicroUSB cable x 1 (Rs.1000)

Costs as of 2024 in Sri Lanka

Design Considerations

The ESP32 Dev Kit V1 is a powerful and versatile development board based on the ESP32 microcontroller, which features dual-core processing, integrated Wi-Fi, and Bluetooth capabilities. Operating at 3.3V and equipped with a USB interface, the board allows for easy programming and debugging. These built-in features are ideal for this application, eliminating the need for physical modifications to any components.

• Power Supply: The receiver device is powered via a MicroUSB cable connected to a mains power adapter, ensuring it can meet the higher power consumption demands required for continuous operation.

Component Connections

LoRa Module: The LoRa Ra-02 module is connected to the ESP32 via standard SPI pins, with the chip select (CS) pin connected to GPIO 5.

• MOSI: GPIO 23
• MISO: GPIO 19
• SCLK: GPIO 18
• CS: GPIO 5
• RST: GPIO 14
• DIO0: GPIO 4

RTC Module: The DS1307 RTC is connected to the ESP32 via the I2C interface, ensuring accurate timekeeping.

• SDA: GPIO 21 (default)
• SCL: GPIO 22 (default)

Using the PCB

• Just like for the Sensor module circuit, there is a PCB version of the receiver circuit is also available on our repo.

• All module placements are marked on the PCB.

• You should only solder female pin headers to the relevant placements and plugin the relevant modules.

• Refer the PCB_Instructions for instructions on how to get the PCB manufactured.