Microcontroller Programming

We covered the basics of programming, the Arduino board, and electronics.

Arduino Program

The assignment was to program an Arduino board to do something, so I decided to adjust the speed of my kinetic scultpure from last week. Due to the unadjustable 5V power source, the flower bloomed at an extremely fast (unideal) speed...

In lab, we used a potentiometer to allow a user to dynamically control the brightness of an LED. A potentiometer is a variable resistor with three pins. When the external sides of the potentiometer are connected to voltage and ground, the middle leg will give the difference in voltage as you turn the knob. analogRead() outputs a value between 0 and 1023, a representation of the voltage on the pin.

We also used the L9110 H Bridge Power Driver to control the speed and direction of a motor. The analogWrite() function uses a technique called Pulse Width Modulation (PWM). PWM turns the output pin HIGH and LOW over a fixed period of time in extremely fast intervals. The percentage of time a pin is HIGH in a period is called duty cycle. The argument of analogWrite() that controls this setting takes values between 0 and 255.

Combining these two techniques, I built a circuit that uses a potentiometer to control the speed of the motor's rotation! I also made a few modifications for my use case:

• The digital pins on the Arduino did not supply enough current to turn a motor (the LED required much less current), so I had to edit the circuit so that the motor also used the 5V pin.

• The motor did not turn with less than ~100 speed. Hence, instead of mapping the 0-1023 range of the potentiometer to the full range of 0-255 speed, I mapped it to 100-255. This way, no matter where the user turns the potentiometer knob, the flower will always be blooming. :)

I found the serial prints really helpful for debugging and making sure that my potVal and motorVal variables were updating correctly. My final code is below:

    const int potPin = A0;  // define Analog In pin A0 for the potentiometer
    int potVal;
    const int motorPin = 6; // define Digital pin 6 for the motor
    int motorVal;

    void setup() {
        // runs once
        Serial.begin(9600);
        pinMode(potPin, INPUT);    // specify potPin as input
        pinMode(motorPin, OUTPUT); // specify motorPin as output
    }
    
    void loop() {
        // loops forever
        potVal = analogRead(potPin); // read in the potVal from potPin
        motorVal = map(potVal, 0, 1023, 100, 255); // map potVal range to motorVal range
        analogWrite(motorPin, motorVal); // write the motorVal to motorPin
        Serial.println(motorVal);  // optional print statement, can change motorVal to potVal for debugging
    }
                

Here is a circuit diagram and schematic:

And here's the final product!