Design

Implementation

Following the design of software part of our project, we decomposed the structure of our hardware system into three sections: actuator, sensor and analyser. The analyser part consists of a raspberry pi 4b board with grove hat and fixed 4 pin connectors with built-in analogue-digital converter.

Here is the final photo of our system:

Introducing the Subsystems

The sensors, actuators and analyser combine to create a control environment for the following subsystems:

• Humidity
• Brightness
• Soil Moisture
• Temperature

Humidity Subsystem: This contains 2 fans, 1 DHT11 temperature/humidity sensor and an external power supply. DHT11 sensor will detect whether the humidity is too high, and fans will be activated to exchange air. In addition, stop the fans if the humidity is too low. The 2 fans are connected to a mosfet which takes a PWM signal from the board, and uses an external power to be controlled.

Light Subsystem: This contains one luminosity sensor, external power supply, led strip lights and mosfet to control it. If the brightness is too low, the LED brightness will increase and vice versa.

Water Subsystem: This is made up of a soil moisture sensor, a water pump, a relay to control the DC motor, and an external power supply. The soil moisture sensor would detect and return a signal to the system, which will be received by the water analyser. The relay sends data input from the raspberry pi hat, the power supply and the positive/negative dc socket connection to the water pump through a jumper wire. For the pump to work, there is only one signal coming from the hat. The signal is on or off and cannot have a velocity value.

Water Capacity Subsystem: This contains a water level sensor connected to the raspberry pi. This subsystem exists to warn users if the water level of the water supply container is too low and needs refilling. The water level sensor contains 3 pins: power in, power out and analog out. The analog signal is transferred into digital signal by the hat and sent to the board.

Hardware Inforamtion

Raspberry Pi 4B

• Processor: Broadcom BCM2711, Quad core Cortex-A72 (ARM v8) 64-bit SoC @ 1.5GHz
• Ram: 4GB LPDDR4-3200 SDRAM
• Internet: 2.4 GHz and 5.0 GHz IEEE 802.11ac wireless, Bluetooth 5.0, BLE Gigabit Ethernet
• Ports: 1 USB 3.0 ports; 1 USB 2.0 ports; Raspberry Pi standard 40 pin GPIO header; 2 × micro-HDMI ports; 2-lane MIPI DSI display port; 2-lane MIPI CSI camera port; 4-pole stereo audio and composite video port
• Video Decoding: H.265 (4kp60 decode), H264 (1080p60 decode, 1080p30 encode)
• Storage Port: Micro-SD card slot for loading operating system and data storage
• Power: 5V DC via USB-C connector (minimum 3A*); 5V DC via GPIO header (minimum 3A*); Power over Ethernet (PoE) enabled (requires separate PoE HAT)
• Operating temperature: 0 – 50 degrees C ambient