5mm Photoresistor LDR Sensor (Pack of 2)

Prototyping and Engineering Tips from Robogears

• The Voltage Divider: To read an LDR with an Arduino, you must use a voltage divider. Connect one end of the LDR to 5V and the other end to an Analog Pin (like A0). Also, connect a 10kΩ fixed resistor from that same Analog Pin to Ground. This creates a measurable voltage that changes with light.

• Calibration in Code: Use the analogRead() function to see the raw values (0-1023). For a "Darkness Sensor," check if the value falls below a certain threshold (e.g., < 300) to turn on an LED or a relay.

• Response Lag: LDRs have a "memory effect" and take a few milliseconds to settle after a sudden change in light. If you need to detect high-speed light pulses (like fiber optic data), use a Photodiode or Phototransistor instead.

• Directional Shielding: If your LDR is being "tricked" by light from its own LED, place a small piece of black heat-shrink tubing around the 5mm head. This creates a "tunnel" that ensures the sensor only looks in one specific direction.

Package Includes

• 2 x 5mm Light Dependent Resistors (LDR)

Disclaimer

Avoid exposing the LDR to high-intensity lasers at close range, as the heat can permanently damage the Cadmium Sulfide tracks.