WEEK 09 Input Devices

GROUP ASSIGNMENT:

WHEEL ENCODER

I’ll test a wheel encoder that works with a hall effect sensor Datasheet: https://cdn.sparkfun.com/datasheets/Robotics/multi-chassis encoder001.pdf

A Hall effect sensor is a device that detects magnetic fields and converts them into electrical signals. It works on the Hall effect principle, where a voltage difference is generated across a conductor when exposed to a magnetic field. These sensors are commonly used for proximity sensing, speed detection, and current measurement in applications like automotive systems, industrial automation, and consumer electronics.

You can find more information about Hall effect sensors here: https://www.electronics-tutorials.ws/electromagnetism/hall-effect.html

Step 1: Connect the Hall Effect Sensor to the Arduino

Connect Red wire → 5V pin on Arduino.
Connect Black wire → GND pin on Arduino.
Connect White wire → Arduino digital pin 2.

Step 2: Upload the Arduino Code (Arduino IDE)

int hallSensor = 2;  // White wire connected to pin 2
void setup() {
    pinMode(hallSensor, INPUT_PULLUP);  // Enable internal pull-up resistor
    Serial.begin(9600);  // Start serial communication
}
void loop() {
    int sensorValue = digitalRead(hallSensor);  // Read sensor output
    Serial.println(sensorValue);  // Print the value to the Serial Monitor
    delay(100);  // Small delay to avoid too much data
}

Step 3: Test the Sensor with Serial Monitor

Click on Tools > Serial Monitor.
You should see 0s and 1s printed when moving the magnet around the sensor
- "1" means NO magnetic field detected.
- "0" means a magnetic field is detected.

Step 4: Connect the Oscilloscope

Use Channel 1 (CH1) on your oscilloscope.
Connect the oscilloscope probe as follows:
- Probe tip (hook) → White signal wire (connected to Arduino pin 2).
- Probe ground clip → Arduino GND.

Step 5: Set Up the Oscilloscope

Turn on the GW Instek GDS-1102A-U oscilloscope.
Press "Autoset" to reset settings.

Step 6: Observe the Output on the Oscilloscope

Bring a magnet close to the Hall sensor.
- The output signal should drop to 0V when the magnet is near.
- When you move the magnet away, the signal should return to 5V.
On the oscilloscope screen, you should see a square wave signal when you move the magnet.

Troubleshooting

If no signal appears, adjust the trigger level slightly.
If the signal is too small, increase the VOLTS/DIV setting.

INDIVIDUAL ASSIGNMENT:

TREADMILL KICAD SCHEMATIC AND PCB

THE HALL SENSOR READING ON XIAO

#define HALL_SENSOR_PIN D6  // White wire (signal) from the Hall sensor
#define LED_PIN D7          // LED connected to D7

void setup() {
    pinMode(HALL_SENSOR_PIN, INPUT_PULLUP); // Enable internal pull-up
    pinMode(LED_PIN, OUTPUT);
}

void loop() {
    int sensorState = digitalRead(HALL_SENSOR_PIN);  // Read Hall sensor

    if (sensorState == LOW) {
        digitalWrite(LED_PIN, HIGH);  // Turn ON LED when magnet is detected
    } else {
        digitalWrite(LED_PIN, LOW);   // Turn OFF LED when no magnet
    }

    delay(50);  // Small delay for stability
}

How It Works

When a magnet is near, the sensor output goes LOW, turning the LED ON.
When there’s no magnet, the sensor output goes HIGH, turning the LED OFF.

ADDING the Push Button to Toggle the LED

If you want the push button (D9) to manually toggle the LED, modify the code like this:

#define HALL_SENSOR_PIN D6
#define LED_PIN D7
#define BUTTON_PIN D9

void setup() {
    pinMode(HALL_SENSOR_PIN, INPUT_PULLUP);
    pinMode(BUTTON_PIN, INPUT_PULLUP);
    pinMode(LED_PIN, OUTPUT);

    Serial.begin(115200);  // Start Serial Monitor
}

void loop() {
    int sensorState = digitalRead(HALL_SENSOR_PIN);  // Read Hall sensor
    int buttonState = digitalRead(BUTTON_PIN);      // Read button state

    if (sensorState == LOW || buttonState == LOW) {  
        digitalWrite(LED_PIN, HIGH);  // Turn LED ON
        Serial.println("LED ON");
    } else {
        digitalWrite(LED_PIN, LOW);   // Turn LED OFF
        Serial.println("LED OFF");
    }

    // Print sensor and button states for debugging
    Serial.print("Hall Sensor: ");
    Serial.println(sensorState == LOW ? "ON" : "OFF");

    Serial.print("Button: ");
    Serial.println(buttonState == LOW ? "PRESSED" : "NOT PRESSED");

    delay(300);  // Small delay to avoid spam in Serial Monitor
}

Now Hall Effect Sensor controls the LED, and you can also toggle it with the button. Also Serial monitor will show the status.

FILES:

KICAD

TREADMILL

TREADMILL.ZIP

FLATCAM

TREADMILL

TREADMILL_FC.ZIP

CHECKLIST:

Group assignment:

Probe an input device(s)'s analog levels and digital signals
Document your work on the group work page and reflect on your individual page what you learned

Individual assignment:

Measure something: add a sensor to a microcontroller board that you have designed and read it.

Learning outcomes:

Demonstrate workflows used in sensing something with input device(s) and MCU board

Have you answered these questions?

Linked to the group assignment page.
Documented what you learned from interfacing an input device(s) to your microcontroller and optionally, how the physical property relates to the measured results.
Documented your design and fabrication process or linked to the board you made in a previous assignment.
Explained the programming process(es) you used.
Explained any problems you encountered and how you fixed them.
Included original design files and source code.
Included a ‘hero shot’ of your board.