9. Input devices

Group Assignment

This week, we tested various input devices. As part of the group project, it was decided to test two distance sensors:

Ultrasonic sensor US-100 Y401
Infrared sensor SHARP 2Y0A02

The testing was conducted together with the instructor, without using a microcontroller. An oscilloscope was used for data analysis.

1. Testing the Y401 Ultrasonic Sensor

The US-100 Y401 ultrasonic sensor is a digital sensor. It generates a pulse signal on the Echo output, where the pulse duration corresponds to the distance to the object.

Goal: To check the change in the output signal depending on the distance to the object.

Connected VCC to 5V, and GND to ground.
By generating a signal for Trig using the AFG-2125 function and arbitrary waveform generator from GW INSTEK, we observed the pulses on Echo with an oscilloscope.

2. Testing the SHARP 2Y0A02 Infrared Sensor

The SHARP 2Y0A02 infrared distance sensor outputs an analog signal. The voltage at the Vo output varies depending on the distance to the object, allowing for smooth values to be processed further.

Goal: To determine the relationship between the output voltage and the distance to the object.

Connected VCC to 5V, and GND to ground.
Connected the output pin Vo to the oscilloscope.
Recorded the changes in the output voltage.

Individual assignment

Testing the YF-S201 Water Flow Sensor

For my individual assignment, I decided to test the YF-S201 water flow sensor.

This sensor measures how much water flows through a pipe. It helps to monitor water consumption and detect leaks.

Applications
- Water supply systems
- Smart homes and irrigation systems

How It Works

When water passes through the sensor, an internal turbine starts rotating. A Hall effect sensor detects the rotations and outputs a pulse signal, which can be processed by a microcontroller.

Water Flow Calculation

For one liter of water, the sensor generates 7.5 pulses per second.

Formula for calculating water flow (L/min):
$$ \text{Flow Rate} = \frac{\text{Number of Pulses}}{7.5} $$ where:
- Flow Rate — water flow rate in liters per minute (L/min)
- Number of Pulses — the number of recorded pulses per second

Example Calculation:
- If the sensor detects 75 pulses in one second, the water flow rate will be:
$$ \frac{75}{7.5} = 10 \text{ L/min} $$

First, using Fusion 360, I designed adapters to connect the water flow sensor to the hose. These adapters ensure a reliable and leak-proof connection, taking into account the hose diameter and design strength requirements to prevent leaks. The connection size with the sensor is 1/2 inch, and the thread pitch is 1.75 mm. I used the Thread tool in Fusion 360 to precisely set these parameters when designing the adapters.

After that, I added a narrow part for connecting the hose, using the Extrude and Loft tools to create a smooth transition and ensure a secure connection between the hose and the sensor.

I prepared the parts for printing using Orca Slicer and printed them on the QQidi Q1 Pro 3D printer using PLA plastic.

After printing, I assembled all the components for further testing.

This code was created with the help of ChatGPT and is used to measure water flow using a flow sensor. Here's how it works:

What does the sensor do?
- The sensor generates pulses when water flows through it.
What does the code do?
- The code counts the number of pulses every second and calculates the water flow in liters per minute.
- The results are displayed on the screen.
How does the code work?
- Each pulse increments the counter.
- The code calculates the water flow every second and displays the result on the screen.

// Include necessary libraries
#include <Arduino.h>

#define SENSOR_PIN 26  // Connect the water flow sensor to pin D26

volatile int pulseCount = 0;  // Number of pulses detected
float flowRate;               // Water flow rate in liters per minute (L/min)
unsigned long previousMillis = 0;  // Variable for time tracking
float totalFlow = 0;  // Total water flow in liters

// Interrupt function triggered on each pulse
void pulseCounter() {
    pulseCount++;  // Increment pulse count
}

void setup() {
    Serial.begin(9600); // Initialize Serial Monitor
    pinMode(SENSOR_PIN, INPUT_PULLUP); // Set sensor pin as input with internal pull-up resistor
    attachInterrupt(digitalPinToInterrupt(SENSOR_PIN), pulseCounter, FALLING); // Attach interrupt on falling edge
}

void loop() {
    // Check if 1 second has passed
    if (millis() - previousMillis >= 1000) {
        detachInterrupt(digitalPinToInterrupt(SENSOR_PIN)); // Temporarily disable interrupt for calculations

        // Formula: pulse frequency / 7.5 = flow rate in L/min
        flowRate = (pulseCount / 7.5);

        pulseCount = 0; // Reset pulse counter
        previousMillis = millis(); // Update timer

        totalFlow += flowRate / 50;  // Update total flow calculation

        // Print flow rate and total flow to Serial Monitor
        Serial.print("Flow Rate: ");
        Serial.print(flowRate);
        Serial.println(" L/min");

        Serial.print("Total Flow: ");
        Serial.print(totalFlow);
        Serial.println(" L");

        attachInterrupt(digitalPinToInterrupt(SENSOR_PIN), pulseCounter, FALLING); // Re-enable interrupt
    }
}

Testing with 0.8 liters of water and flow calibration

To test the flow sensor, I used 0.8 liters of water, which I gradually poured into the sensor. Despite attempts to create a uniform flow, the water supply was irregular, which led to differences in the flow readings. To minimize the impact on the results, I calibrated the system by adjusting the coefficient in the total water volume calculation.

The first attempt with the coefficient totalFlow += flowRate / 60 gave inaccurate results. Then I tried using the coefficient 80, but the result was half of the actual amount of water.

Specifically, in the formula totalFlow += flowRate / 50, where totalFlow updates the total water volume, I adjusted the coefficient to improve the measurement accuracy.

To improve measurement accuracy, I repeated the test by changing the coefficient in the total water volume calculation. In the formula totalFlow += flowRate / 50, where totalFlow updates the total water volume, I used a coefficient of 50.

Conclusion

This week, I worked on testing various sensors, such as ultrasonic, infrared, and water flow sensors. My focus was on improving the accuracy of water flow measurements by calibrating the system and adjusting calculation coefficients. After making changes to the coefficients, the accuracy and stability of the measurements improved significantly. The system was able to track the total water volume accurately, even though the flow fluctuated. This confirms that the system is reliable and can handle real-world conditions effectively.