The Dimmer

BRIEF The volume knob's secret

Think about a volume knob. It is not on or off, it lives everywhere in between. Today you wire the kit's twisty knob (its proper name is a potentiometer) and use it to dim an LED smoothly from off to full blaze, like the lights in a cinema before the movie. On the way you learn the difference between the two languages electronics speaks: digital and analog.

Time: 45–60 minutes · Difficulty: 2/5 · You need: Lesson 03 done.

KIT What you need

• R3 board with USB cable
• Breadboard
• 1 LED and its 220Ω resistor
• The potentiometer (blue knob, three legs)
• Jumper wires

BUILD Wire it

Unplug the USB first. Push the potentiometer's three legs into three separate breadboard rows.

From	To	Why
Potentiometer left leg	R3 5V	One end of the ramp: full power
Potentiometer right leg	R3 GND	Other end of the ramp: zero
Potentiometer middle leg	R3 pin A0	The slider that rides the ramp
R3 pin 9 (has the ~ mark)	Resistor → LED long leg	A PWM pin, so it can dim
LED short leg	R3 GND	Loop complete

CODE Program it

// GAMERIFT Beginner Kit, Lesson 04: The Dimmer
// Read a knob, dim a light. Analog in, PWM out.

const int knobPin  = A0;
const int lightPin = 9;   // must be a ~ pin for PWM

void setup() {
  pinMode(lightPin, OUTPUT);
  Serial.begin(9600);        // open a chat window to the computer
}

void loop() {
  int knob = analogRead(knobPin);              // 0 to 1023
  int bright = map(knob, 0, 1023, 0, 255);   // translate rulers

  analogWrite(lightPin, bright);               // the PWM trick

  Serial.print("knob: ");                      // spy on the numbers
  Serial.println(knob);
  delay(50);
}

1. Upload, then open Tools → Serial Monitor (set it to 9600 baud, bottom right).
2. Twist the knob slowly. Watch the number glide from 0 to 1023 while the LED breathes brighter and dimmer under your fingertips.
3. The Serial Monitor is your new best friend. When a circuit misbehaves, printing the numbers is how you see what the board sees.

BREAK IT Now break it on purpose

1. Swap the potentiometer's outer legs (5V and GND). Nothing breaks, but the knob now works backwards. Every dimmer installer has done this at least once.
2. Move the LED wire from pin 9 to pin 12 (no ~ mark) and change the code to match. The smooth dim becomes a crude on/off around half way. Now you know why the ~ pins matter.
3. Pull the middle leg wire out. A0 is now floating, watch the serial numbers wander on their own, haunted by static. Same ghost you met in Lesson 03.

REMIX Make it yours

• Cinema mode: when the knob hits zero, make the LED do one slow farewell blink before going dark, like house lights before a movie.
• Speed dial: instead of brightness, let the knob control how fast the LED blinks, from sleepy to frantic. Hint: use the knob value as the delay.
• Two zones: add your second LED on pin 10 (also a ~ pin). Knob low, only lamp one glows. Knob high, both blaze. Build the logic yourself.

LOG IT Show and tell

Film 15 seconds of your remix and save it for your lesson log. Stuck? Send a photo of your wiring via contact us, a real person will spot it.