YouTube Video: https://www.youtube.com/watch?v=1OjPXJKbuPw

Introduction

This project involves two liquid-filled reservoirs, labeled A and B. Reservoir A serves as a supply tank, and its liquid level is not critical. Reservoir B, however, requires a stable liquid level, which is the primary control objective. An ultrasonic distance sensor is mounted vertically above Reservoir B to measure the liquid depth, providing distance readings denoted as x₁. A peristaltic liquid pump connects the two reservoirs. The pump's role is to transfer excess liquid from Reservoir B to Reservoir A or to draw liquid from Reservoir A to replenish Reservoir B, depending on the measured liquid level.

📐 PID Control

To maintain the desired liquid level in Reservoir B, a PID (Proportional-Integral-Derivative) control algorithm is implemented. The controller minimizes the error between the setpoint and the measured value by adjusting the pump's operation. The PID control law is defined as:

u(t) = Kp * e(t) + Ki * ∫e(t)dt + Kd * de(t)/dt

Where:

• e(t) is the error between the measured and target level (e.g., e(t) = x₁ - target)
• Kp is the proportional gain
• Ki is the integral gain
• Kd is the derivative gain
• u(t) is the output used to determine the pump’s direction and speed (via PWM)

This PID controller ensures that the liquid level in Reservoir B remains stable despite disturbances or changes in system dynamics.

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✅ Requirements

Software

• GNU Octave (Tested on version 10 (2025-03-25))
• Arduino IDE (Tested on version 1.8.19 (Store 1.8.57.0))
• USB connection to Arduino board (Uno, Nano, etc.)
• instrument-control package for Octave

Hardware

• Arduino Uno
• HC-SR04: Ultrasonic Sound Sensor
• L298N: H BRIDGE
• 12V 3x5 PUM: Peristaltic Water Pump
• 12V ADAPTER: Power Supply for the Pump
• 9V BATTERY: Power Supply for Arduino

Connection Map

Here is the connection map of the system:

COMPONENT	DESCRIPTION	COMPONENT PIN	CARD PIN	CARD
HC-SR04	Ultrasonic Sound Sensor	TRIG	D6	UNO
HC-SR04	Ultrasonic Sound Sensor	ECHO	D7	UNO
L298N	H BRIDGE	IN1	D8	UNO
L298N	H BRIDGE	IN2	D9	UNO
L298N	H BRIDGE	ENA	D10 (PWM)	UNO
12V ADAPTER	POWER SUPPLY	+ / -	L298N
12V 3x5 PUMP	Peristaltic Water Pump	+	OUT1	L298N
12V 3x5 PUMP	Peristaltic Water Pump	-	OUT2	L298N

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🛠️ Installation

Follow the steps below to set up the environment for PID-controlled liquid transfer.

📦 Octave Setup

1. Install the instrument-control package:

   pkg install -forge instrument-control
   pkg load instrument-control

2. Clone this repository or download the source code:

   git clone https://github.com/DevBD1/PID_Controlled_Liquid_Transfer.git
   cd PID_Controlled_Liquid_Transfer

3. (Optional) If you have .env or calibration constants, place them in the root folder.

4. Make sure your Arduino is connected via COM3 or change the port in the script:

   s = serialport("COM3", 9600);

🔌 Arduino Upload

1. Open arduino/transfer_serial.ino in Arduino IDE.
2. Select your correct board and COM port.
3. Upload the sketch.

🧪 First Start

To test the system and determine the standard deviation of sensor inputs:

1. Run matlab/standard_deviation/log_realistic.m script
2. Input the direction of the pump for test
3. Input the repeat count
4. Check the generated .csv file
5. Run matlab/standard_deviation/analyse.m script
6. Read the output, the script will generate a variable at the end
7. Check the generated pid_tolerance.mat file

To start full PID control:

1. Run matlab/pid_control_serialport_mapped.m script

pid_control_serialport_mapped.m

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⚙️ Configuration

You can modify the PID constants and port settings at the top of the .m files:

Kp = 40;
Ki = 0.5;
Kd = 20;

s = serialport("COM3", 9600);  % Change if needed

Use log_static.m when the reservoir B is empty. The result is your max. height.

🧪 Other Scripts

• Fill or Empty -> dir: .../matlab/fill_or_empty.m
• Stop -> dir: .../matlab/stop.m