TerraSync — Technical Implementation

Circuit design & firmware

Full implementation details for the physical computing layer: schematics, resistor calculations, and the Arduino firmware that drives TerraSync's ambient sensing and focus interaction.

Components

Bill of materials

TerraSync's circuit uses a minimal set of components — a photoresistor for ambient sensing, a push button for focus state control, and three LEDs to produce warm, diffused light under the dome.

Arduino Uno Microcontroller. Handles sensor reads, LED output, and serial comm to Unity.
Photoresistor (LDR) Analog input on A0. Reads 0–1023 based on ambient brightness.
Push Button Digital input on pin 2, using INPUT_PULLUP. Controls focus state toggling.
White LED PWM pin 9. Contributes to the warm dome glow.
Yellow LED PWM pin 10. Warm amber tone for evening light feel.
Blue LED PWM pin 11. Adds a cool undertone to balance the dome lighting.
220Ω Resistors ×3 Current limiting for each LED. Chosen after Ohm's law calculation.
10KΩ Resistor Voltage divider for photoresistor analog read.

Schematic

Circuit design

All components share a common ground rail. The button uses the Arduino's built-in INPUT_PULLUP — no external pull-down needed. The photoresistor is paired with a 10KΩ resistor to form a voltage divider, and each LED has its own 220Ω current-limiting resistor.

TerraSync circuit schematic
Schematic overview. Shared ground simplifies the layout; PWM pins 9, 10, and 11 enable smooth brightness fading via analogWrite().
TerraSync breadboard circuit
Assembled circuit. Alligator clips extend the button and photoresistor outside the breadboard so they sit flush with the lamp exterior. Blue, white, and yellow LEDs produce a layered warm-cool glow under the dome.

Resistor calculations

Ohm's law

Each LED required a current-limiting resistor sized to keep the LED safe without sacrificing too much brightness. Using R = (Vs − Vf) / I, 220Ω was the closest standard value that kept current safely under the LED's rated limit.

LED Forward Voltage (Vf) Target Current Calculated R Chosen R
White 3.2 V 20 mA ~90 Ω 220 Ω
Yellow 2.0 V 20 mA ~150 Ω 220 Ω
Blue 3.2 V 20 mA ~90 Ω 220 Ω

220Ω was chosen for all three LEDs because it's the nearest standard value that keeps current safely within spec for each LED type — and using the same value across all three simplified the build without any meaningful tradeoffs in brightness.

Ohm's law handwritten calculations
Handwritten Ohm's law calculations. Also includes a worked example for the photoresistor's voltage divider R2 at medium ambient brightness.

Arduino firmware

Sensor logic & serial output

The firmware reads both inputs on each loop cycle, maps the photoresistor value to LED brightness (inverting so darkness = bright LEDs), then sends a compact serial string for Unity to parse. A 20ms delay reduces debounce noise on the button.

TerraSync.ino Arduino C++ 
/*
  Valentina Filizola
  TerraSync — HCDE 439 Final Project
*/

// Pin definitions
const int lightSensorPin = A0;   // photoresistor
const int buttonPin = 2;          // button

// LED pins
const int led1 = 9;    // white LED
const int led2 = 10;   // yellow LED
const int led3 = 11;   // blue LED

void setup() {
  Serial.begin(9600);                   // match Unity serial speed
  pinMode(buttonPin, INPUT_PULLUP);     // built-in pull-up, no ext. resistor
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
}

void loop() {
  int lightValue  = analogRead(lightSensorPin);  // 0–1023
  int buttonState = digitalRead(buttonPin);

  int buttonPressed = (buttonState == LOW) ? 1 : 0;

  // Constrain range — LEDs dim earlier, stay bright in darkness
  int constrainedLight = constrain(lightValue, 0, 600);

  // Invert: dark room → full brightness
  int brightness = map(constrainedLight, 0, 600, 255, 0);

  analogWrite(led1, brightness);
  analogWrite(led2, brightness);
  analogWrite(led3, brightness);

  // Serial output format Unity expects: "L:512,B:0"
  Serial.print("L:");
  Serial.print(lightValue);
  Serial.print(",B:");
  Serial.println(buttonPressed);

  delay(20);   // debounce buffer
}

In operation

Circuit behavior

The GIF below shows the full sensing loop in action — photoresistor driving LED brightness while the button state is transmitted to Unity. Covering the sensor dims the room, triggering the LEDs to glow and shifting the Unity scene to its night state.

TerraSync circuit in operation