Assignment 5: Higher voltage and transistors!

Images:

Picture of my circuit. The ultrasonic sensor measures the distance of whatever is in front of it, and outputs the delay between its outgoing ping and the return echo in milliseconds. Using the speed of sound, this duration can be converted into a distance which is used to activate the buzzer. The buzzer pitch is controlled by a transistor, separately from the constant 5V power supply.

Hand drawn circuit diagram

This diagram shows the three parts of my circuit: the 9V power source connected to the Vin pin, the ultrasonic sensor, and the transistor-controlled buzzer. The specific transistor used in this circuit has a maximum current of around 30A, which is much higher than any possible current from the Arduino (measured in mA). In my circuit, the transistor's role is more to control the buzzer instead of handing a significantly higher load power.

Code:

Note: The A5 assignment description says to use analogWrite. I realized this very late and was somewhat running out of time so I'm aware that it's something missing from my submission.

 
    // Uses an ultrasonic sensor to measure distance and changes the pitch of an active buzzer when
    // a distance of 10 inches or less is detected.
    // Uses some code from the built-in Ping example.

    const int buzzer = 9; // Identify buzzer pin
    const int sensorPower = 10; // Identify sensor power pin
    const int trig = 11; // Identify sensor "trig" pin
    const int echo = 12; // Identify sensor "echo" pin

    void setup() {
        pinMode(buzzer, OUTPUT); // Set buzzer pin to output
        pinMode(trig, OUTPUT); // Set trig pin to output (sending signals)
        pinMode(echo, INPUT); // Set echo pin to input (receiving signals)
        pinMode(sensorPower, OUTPUT); // Set sensor power pin to output
        digitalWrite(sensorPower, HIGH); // Output power to ultrasonic sensor
    }

    void loop() {
        long duration, inches; // Set up variables for measurements
        digitalWrite(trig, LOW); // Reset the sensor ping
        delay(5); // Wait 5 ms
        digitalWrite(trig, HIGH); // Trigger the sensor to send a ping
        delay(5); // Wait 5 ms
        digitalWrite(trig, LOW); // Deactivate the sensor

        duration = pulseIn(echo, HIGH); // Read the sensor output
        inches = microsecondsToInches(duration); // Convert duration to distance

        if (inches < 10L) { // If the measured distance is less than 10 ms
            digitalWrite(buzzer, LOW); // Change the buzzer pitch
        }

    delay(490); // Wait 490 ms
    digitalWrite(buzzer, HIGH); // Reset the buzzer pitch
    }

    // Converts the microsecond delay between the ultrasonic sensor's ping and the return echo to
    // a distance in inches.
    // Parameter: long microseconds: Duration from the initial sensor ping to the return echo
    // Returns a long value for distance in inches
    long microsecondsToInches(long duration) {
        return duration / 74 / 2; // Convert the duration to distance
    }

Responses:

1. For the specific transistor, the absolute maximum current listed is 80A when pulsed with a 1% duty cycle.

2. Schematic:
Circuit diagram for question 2
Parts:

Arduino Uno
28BYJ-48 motor
1N4007 diode
104pf capacitor

3. Schematic:
Circuit diagram for question 3
The Arduino controls the L293 chip's In1 and In2 pins. Here's example code for moving the motors in different directions:

 
    // Initialize pins:
    Assign pins for In 1/2 L/R

    // Both motors stopped:
    All pins off
    Wait
    
    // Both motors forwards:
    In1L/R on, In2L/R off
    Wait

    // Both motors backwards:
    In1L/R off, In2L/R on
    Wait

    // Motors moving in different directions:
    In1L on, In2L off
    In1R off, In2R on
    Wait
    In1L off, In2L on
    In1R on, In2R off
    Wait

    // Stop both motors again:
    All pins off
    Wait

4. I did not use any AI tools while completing this assignment.

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