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Light-Tracking Servo (Arduino)

Aim a servo toward the brighter of two photoresistors — the core of a solar tracker. Learn to compare two analog inputs.

Intermediate30 min

What you need

Wiring

Arduino Uno
SG90 servo
Photoresistor
Photoresistor

Hover a pin or a wire to trace the connection.

Code

light_tracker.ino
// Turn a servo toward whichever photoresistor sees more light.
#include <Servo.h>

Servo s;
int pos = 90;  // start centered

void setup() {
  s.attach(9);
  s.write(pos);
}

void loop() {
  int left  = analogRead(A0);
  int right = analogRead(A1);

  if (left - right > 50 && pos < 180) pos++;        // brighter on the left
  else if (right - left > 50 && pos > 0) pos--;     // brighter on the right
  s.write(pos);
  delay(20);
}

Steps

  1. Build two LDR dividers: each LDR from 5V to its analog pin (A0, A1), with a 10kΩ from that pin to GND.
  2. Mount the two LDRs angled apart on the servo horn so each sees a different side.
  3. Wire the servo signal to D9, power to 5V/GND.
  4. Upload — the servo turns toward the brighter side. Tweak the `50` dead-zone to taste.