Assignment 2: Fade!

Images:

My circuit setup, with a 4-pin RGB LED set up to detect a signal from a button.

Circuit diagram

This diagram is a representation of the above circuit, showing the button providing a signal to Pin 2 and the RGB LED. Note that the button resistor value of 10K Ω is to limit the maximum current for the pin to 100 mA, while the LED resistor values are calculated to best limit the current to a maximum of 20 mA.

Code:


        // Gradually lights up and turns off a 4-pin RGB LED with the push of a button
        // Partly based on the Arduino built-in "Button" example

        // Constants used to identify specific pins
        const int buttonPin = 2; // number of the pushbutton pin
        const int redPin = 3; // number of the red LED pin - PWM pin
        const int grnPin = 4; // number of the green LED pin
        const int bluPin = 5; // number of the blue LED pin - PWM pin

        // Changing variables
        int buttonState = 0;  // variable for reading the pushbutton status

        void setup() {
          pinMode(redPin, OUTPUT); // Initialize the red LED output
          pinMode(grnPin, OUTPUT); // Initialize the green LED output
          pinMode(bluPin, OUTPUT); // Initialize the blue LED output
          pinMode(buttonPin, INPUT); // Initialize the button pin as an input
        }

        void loop() {
          buttonState = digitalRead(buttonPin); // Read the button value

          // Turns on all LEDs if the button is pushed (3s)
          if (buttonState == HIGH) { // If the button is pushed (state is HIGH)
            for(int i = redPin; i <= bluPin; i++) { // Cycle through all LEDs
              digitalWrite(i, HIGH); // Turn on (state HIGH) the current LED
              delay(1000); // Wait 1s before turning on the next LED
            }

            // Simulates a duty cycle to reduce the brightess (1.7s)
            for(int i = 100; i > 0; i--) { // Duration of lower brightness
              digitalWrite(redPin, LOW); // Turns off the red LED
              digitalWrite(grnPin, LOW); // Turns off the green LED
              digitalWrite(bluPin, LOW); // Turns off the blue LED
              delay(15); // 15ms off
              digitalWrite(redPin, HIGH); // Turns on the red LED
              digitalWrite(grnPin, HIGH); // Turns on the green LED
              digitalWrite(bluPin, HIGH); // Turns on the blue LED
              delay(2); // 2ms on
            }

            // Uses analogWrite on the PWM pins to reduce brightness (0-256)
            analogWrite(redPin, 50); // Red LED duty cycle
            analogWrite(bluPin, 50); // Blue LED duty cycle
            delay(1700); // Wait 1.7s

            // Turn off the LEDs
            digitalWrite(redPin, LOW); // Turns off the red LED
            digitalWrite(grnPin, LOW); // Turns off the green LED
            digitalWrite(bluPin, LOW); // Turns off the blue LED
          } else { // If the button state is LOW
            // Turn off the LEDs
            digitalWrite(redPin, LOW); // Turns off the red LED
            digitalWrite(grnPin, LOW); // Turns off the green LED
            digitalWrite(bluPin, LOW); // Turns off the blue LED
          }
        }

Responses:

Calculations:
The red and green LEDs both require 1.8V and a current of 20 mA, so as with the last assignment I used this formula: 5V - 1.8V / 20 mA = R = 160 Ω
However, the blue LED requires 3.2V, so the formula used would be: 5V - 3.2V / 20 mA = R = 90 Ω
As mentioned above, a resistance of 10K Ω is used to limit the button pin current to about 100 mA, which is a safe value.

1. Graph: Chart of different analogWrite values An analogWrite of 64 corresponds to 25%, 128 to 50%, and 255 to 100% duty cycles. I represented the different lengths by showing what a single duty cycle would look like with all analogWrite values overlaid, so the shortest turns off first and the longest stays on consistently.

2. Each of the three LEDs making up a color in the RGB LED draws 20 mA, so by following the code it's possible to approximate how long it would run with a 1200 mAh battery.
Firstly, turning on the LEDs one by one means one LED runs for 3s, one runs for 2s, and one runs for 1s, for a total of 120 mA over 3 seconds. Next, the duty cycle runs 100 times with the LEDs all on for 2ms each time, leading to 12 mA in this period for a total of 1.7 seconds. Finally, the analogWrite function uses a duty cycle of 50/255 to reduce the PWM pins' brightness, so for an additional 1.7 seconds the red and blue LEDs' current is reduced to about 19.6%. In this period the LEDs draw about 34 + 2(6.7) = 47 mA. In total, the LEDs draw about 120 + 12 + 47 = 179 mA over a period of 6.4 seconds. Therefore, the 1200 mAh battery (72,000 mA minutes or 4,320,000 mA seconds) would power this circuit for about 43 hours: 4,320,000/(179/6.4) = 154,458s = 42.9 hours.

3. I used my multimeter to test one of the 1.8V LEDs in a circuit with a 220 Ω resistor. I measured an actual value of about 3.9V, versus the theoretical forward voltage of 3.2V. I would attribute this mismatch to differences between the hardware and the ideal calculations which I made earlier.

4. I did not use any AI tools during this assignment.

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