WEEK 16 SYSTEM INTEGRATION

1. INTRODUCTION
2. SCHEMATIC & SYSTEM OVERVIEW
3. DESIGN
4. SYSTEM LOGIC & OPERATION
5. RENDERING & VISUALIZATION
6. PROJECT MANAGEMENT & TIMELINE
7. INVENTORY & BILL OF MATERIALS (BOM)

INTRODUCTION

The Problem

In most households, a significant amount of water is wasted while waiting for it to reach the desired temperature.

When the hot water tap is turned on, liters of cold water—already sitting in the pipes—flow directly down the drain before the heated water finally arrives.

This inefficiency results in both resource waste and unnecessary wait times.

The Solution

My project addresses this issue by implementing a water recirculation and pre-heating system.

The goal is to circulate water through the pipes to prime them while the tap remains closed. By the time the user opens the faucet, hot water is delivered instantaneously, preventing the waste of treated water and optimizing domestic energy use.

SCHEMATIC & SYSTEM OVERVIEW

In a standard residential setting, the plumbing installation typically follows the layout shown in the schematic below:

System Integration

My system is designed to be installed at one of the faucet nodes, enabling water recirculation through the existing cold water lines. This configuration allows the system to bypass the traditional drainage route, as illustrated in the following schematic:

DESIGN

The design is comprised of straightforward components, organized into two distinct subsystems:

Plumbing & Hydraulics

The hydraulic system relies on two primary components:

• Water Pump: Responsible for driving the water recirculation through the circuit.
• Solenoid Valve: Acts as the primary control gate. Its function is to close the connection between the hot and cold water lines when the system is in standby mode, preventing backflow or unintended mixing.

Electronics & Power Supply

The electrical subsystem is composed of the following core elements:

• Power Supply Unit (Transformer): A dual-voltage setup designed to power the control electronics at 5V and provide 24V for the pump and solenoid valve.
• Control Board: A custom PCB (or development board) featuring the RP2040 microcontroller, which manages the system logic and I/O.
• Temperature Probe: A dedicated sensor integrated into the hydraulic circuit to monitor the temperature of the recirculating water in real-time.

The temperature probe is strategically positioned between the pump and the solenoid valve for optimal thermal reading.

SYSTEM LOGIC & OPERATION

The system operates under a straightforward yet precise logic, which is detailed in the functional block diagram below:

Sequence Description

1. IDLE State (Standby)
• Condition: System is OFF
• Trigger: Start button is pressed AND Temperature is below 35°C
• Action: Pump and Valve are energized simultaneously. Transition to RUNNING state
2. RUNNING State (Active Operation)
• Monitoring: The system continuously polls the temperature sensor and internal timer
• Exit Conditions:
1. Temperature reaches >= 45°C (Overheat protection/Target reached)
2. Start/Stop button is pressed again (Manual override)
3. Time elapsed exceeds 5 minutes (Safety timeout)
• Action: Transition to SHUTDOWN state
3. SHUTDOWN State (Sequential Stop)
• Step A: The Pump is turned OFF immediately to stop fluid flow
• Step B: A non-blocking timer starts for a 5-second delay (to depressurize or clear the line)
• Step C: The Valve is turned OFF
• Final Action: System returns to IDLE state, ready for the next cycle

RENDERING & VISUALIZATION

The following AI-generated image illustrates the final assembly, showcasing the full integration of the hydraulic and electronic subsystems into a functional prototype:

Conceptual render of the integrated system, featuring the RP2040 control unit, the 24V power stage, and the recirculating hydraulic circuit.

PROJECT MANAGEMENT & TIMELINE

To be honest, this assignment has been the most challenging so far, as defining the starting point was a complex task.

The requirement is to establish a working plan for the Final Project, and considering my current time constraints, I have dedicated a single week of vacation to develop the entire workflow.

My primary milestones for this intensive week are:

1. Electronics Design & Production: Designing the custom PCB and completing the fabrication process.
2. Enclosure Design & 3D Printing: Designing and manufacturing the housing for the integrated system.
3. Hydraulic Assembly: Integrating the plumbing components into the main enclosure.
4. Wiring & System Testing: Completing the electrical connections and performing functional tests.

Current Challenges:

As of today, the selection of materials for the electronics housing and the specific mounting mechanisms are still under evaluation. This uncertainty is part of the iterative design process I am currently navigating.

INVENTORY & BILL OF MATERIALS (BOM)

At this stage, the confirmed costs for the main components are as follows:

• Recirculation Pump: €30.49
• Solenoid Valve: €29.99

For the remaining components, the following estimated prices are being used for the initial budget:

• Seeed Studio XIAO RP2040: $5.40
• NTC Thermistor (10kΩ, 3750K, 1206 package): $1.89

As the project documentation progresses and the design is finalized, I will update this list with the remaining parts and exact costs.